DEVELOPMENT OF STRENGTH AND DURABILITY OF CONCRETE...

DEVELOPMENT OF STRENGTH AND DURABILITY OF CONCRETE

INCORPORATING LOCAL METAKAOLIN

MUHAMMAD BURHAN SHARIF

2005-Ph.D-CIVIL-06

SUPERVISOR

PROF. DR. MUHAMMAD AKRAM TAHIR

DEPARTMENT OF CIVIL ENGINEERING UNIVERSITY OF ENGINEERING AND TECHNOLOGY

LAHORE, PAKISTAN

2011

This dissertation is dedicated to my parents for their constant encouragement, to my wife for her patience and my kids for missing their father most of the time during these difficult years.

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ACKNOWLEDGEMENT

Alhumdulillah all praises and gratitude to the Almighty Allah who has given the

author the courage and tenacity to complete his research thesis.

The author is extremely thankful to his advisor Prof. Dr. M. Akram Tahir for his

encouraging attitude, patience, sound guidance and valuable advice to complete this

research. His constant supervision and guidance helped the author to complete the

research, which was otherwise not possible. The author feels very proud to have worked

under his guidance and consider it a special blessing of God. Due to his benign patronage

and able coaching author has been able to finish the research successfully and it is a great

privilege to acknowledge his guidance. The author is also thankful to the external

examiners Prof. Dr. Ueda Tamon of Hokkaidu University, Prof. Dr. Arif Masud of

University of Illinois and Prof. Dr. Abdullah Saand of Quaid-e-Awam University for

spending their valuable time.

The author owes his deepest gratitude to late Prof. Dr. M. Ashraf for his

encouraging attitude towards the research students. He was chairman of the department

and he regularized smooth procedure for the research students of the department. I will be

indebted for his positive attitude regarding research facilities and funding for the research

students throughout my life.

The author is grateful to Prof. Dr. Abdul Sattar Shakir and Prof. Dr. M. Ilyas for

their valuable advice and constant encouragement during this research work. The author

is also very thankful to the teachers of the Civil Engineering department for their valuable

suggestions and encouragement. He is also obliged to his research fellow Engr. Abdul

Ghaffar for his assistance in experimental work.

The author would like to thank the staff of concrete laboratory for their

cooperation in successful completion of the research. Author takes this opportunity to

thank the administrative staff of the university in general and that of the Civil Engineering

Department in particular for extending their full cooperation and help in completing the

administrative requirement for this study.

Finally the author is very thankful to his parents, wife, sister, brother and his kids,

who always pray for his success and have been a constant source of encouragement.

Muhammad Burhan Sharif

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ABSTRACT

Ordinary Portland cement concrete is a very popular construction material used in

developed/underdeveloped countries. The basic ingredients of concrete are cement, fine

and coarse aggregates bounded by water. Fine and coarse aggregates are generally inert

materials which do not react with cement during hydration process rather act as filler

material. Ordinary Portland cement (OPC) concrete is good for normal construction;

however, for industrial construction OPC concrete may come in contact with different

types of aggressive environment such as acid producing or acid based industries, fruit and

vegetable processing industries, underground structures subjected to water logging and

salinity which results in degradation of concrete. Corrosion of reinforcement for exposed

portion of concrete structure is also very important especially in case of concrete highway

bridges or other important heavy structures.

Supplementary cementing materials (SCM’s) are commonly used to improve strength and

durability of concrete. The incorporation of these materials also reduces the cost of the

concrete. The most commonly used SCM’s are silica fume, fly ash, blast furnace slag,

metakaolin, rice husk ash etc. These SCM’s are finer than cement and hence improve the

packing of the concrete mixture, resulting in increased compressive strength. The

durability of concrete containing SCM’s is improved due to the chemical reaction of

various compounds present in supplementary cementing material with cement during the

hydration process. The increase in replacement level of SCM’s by weight with the cement

also influences the strength and durability properties of concrete.

Kaolin clay, a source of metakaolin; has been frequently used in pottery industry and it is

abundantly available in Pakistan; however, it has never been used as supplementary

cementing material by local construction industry. This study was undertaken to assess

the potential of locally produced metakaolin for using as pozzolan especially for

durability of concrete against acid and carbonation attack.

The main objective of the research includes

a) to develop reactive metakaolin from kaolin clay,

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b) to study the performance of metakaolin concrete against acid and carbonation

attacks,

c) to evolve Strength Degradation Model for metakaolin concrete against acid attack.

During the first phase of study, metakaolin was successfully developed from the Nagar

Parkar kaolin. The kaolin was calcined at several temperatures ranging from 600oC to

1000oC for variable durations of 6 to 10 hours. The calcined clay in each case was finely

divided to specific surface of approximately 645 m2/kg. The powdered samples were

subjected to X-ray Diffraction Tests (XRD) as well to Strength Activity Index Tests

(SAI) for 7 and 28 days. It was found from XRD tests that kaolin calcined at 800oC for 8

hour duration was transformed into the most reactive metakaolin. The strength activity

Index tests supported this finding as well.

The performance of metakaolin concrete against acid and carbonation attacks was studied

during the second phase of the study. A huge and exhaustive test program was designed

in which the most reactive metakaolin developed during the first phase was used as

pozzolan. Two broad classes of concretes were prepared with binder contents of 300

kg/m3 and 400 kg/m3 of concrete respectively; the former represented the normal class

concrete and the latter as a rich class concrete. Four metakaolin-binder ratios (0%, 15%,

20% and 25%) were combined with three water-binder ratios (0.45, 0.55 and 0.55) to

produce 12 concrete mixtures from each of the normal and rich class concretes. One

hundred twenty cubes of 100mm size were case from each mixture. Four cubes from each

mixture were crushed at 7 & 28 days to determine the compressive strength. Fifteen cubes

were reserved for carbonation experimentation and three each were used for

determination of carbonation depth in open atmosphere at 4, 7, 13, 25 and 52 weeks.

Sixteen cubes each were immersed in 2, 5 & 8% concentrated solution of sulfuric acid

and an equal number of cubes were placed in 2, 5 & 8% solution of acetic acid. The

compressive strength was obtained after 7, 28, 91 and 182 days of immersion in each

case. It was revealed from the test results that metakaolin concrete better resisted the acid

attack in comparison with the control plain cement concrete

The strength of concrete was degraded due to immersion in acid solution of variable

concentrates. A strength degradation model was proposed using statistical approach. The

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model was based on physical parameters like binder content, metakaolin-binder ratio,

water-binder ratio, solution strength of acid and immersion period. One half of the

experimental data was used in the calibration of the model and the other half was used for

validation of the model. The model prediction agrees quite closely with the experimental

data.

Carbonation depth was measured for concrete cubes exposed to open atmosphere at 4, 7,

13, 25 & 52 weeks interval. The carbonation depth increases with increase in water to

binder ratios but drastically decreases for metakaolin concrete due to the improved

packing of the concrete matrix. The graphical presentation of carbonation depth clearly

demonstrates the role of variable dosage of metakaolin. These charts may also be used as

a ready reference for a fair estimate of carbonation depth for different mixtures of

metakaolin concrete other than specified.

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Table of Contents Chapter Title Page Title Page Acknowledgments i Abstract ii Table of Contents v 1 Introduction 1 1.1 General 1 1.2 Statement of Problem 4 1.3 Objective of Study 5 1.4 Scope of Study 6 2 Literature Review 11 2.1 Introduction 11 2.2 Pozzolan 11 2.3 Pozzolanic Reaction 13 2.4 Metakaolin(Structure & Development) 14 2.5 Strength 17 2.6 Permeability 20 2.7 Resistance to Acid Attack 22 2.8 Shrinkage 24 2.9 Resistance to Alkali Silica Reaction 26 2.10 Resistance to Sulphate Attacks 28 2.11 Carbonation 29 2.12 Freeze-Thaw Resistance 31 2.13 Summary 32 3 Development of Metakaolin 34 3.1 Introduction 34 3.2 Sources of Kaolin 34 3.3 Properties of Raw Kaolin 34 3.4 Production of Kaolin 37 3.5 Characterization by X-ray Diffraction Analysis 39 3.6 Characterization by Mechanical Strength 45 3.7 Discussion on Strength Activity Index Results 50 3.8 Summary 51

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4 Experimental Program 52 4.1 Introduction 52 4.2 Test Program 53 4.3 Physical and Chemical properties of Materials 61 4.4 Test Results for Binder Content 300 Kg/m3 64 4.5 Test Results for Binder Content 400 Kg/m3 87 4.6 Summary 111 5 Development of Model 113 5.1 Introduction 113 5.2 The Model 113 5.3 Calibration and Validation of Model 131 5.4 Carbonation 148 5.5 Discussion on Carbonation Results 150 5.6 Summary 153 6 Conclusions and Recommendations 154 6.1 Conclusions 154 6.2 Recommendations for future study 155 References 156 Appendix A 164

CHAPTER-1

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INTRODUCTION

1.1 GENERAL

Concrete, basically made of Portland cement, aggregates, and water, is one of the most

versatile construction materials. In its present form it has been used partially or

completely in many structures for more than one century. Compared to other major

construction materials such as steel, polymeric materials, and composites, concrete is the

most ecologically friendly, needs the least amount of energy to produce, and can be

proportioned to possess high strength. This aim is not only to ensure that the concrete is

capable of withstanding compressive stress but that it is durable as well. In other words,

the compressive strength of concrete is used not only as a basis of structural design and as

a criterion of structural performance, but also as a criterion for the durability of a concrete

structure.

Some significant developments have recently taken place in concrete technology. In the

manufacture of Portland cement, considerable efforts are, therefore, being made to find

substitutes, the so-called supplementary cementing materials (SCM), to replace part of

cement in concrete. Generally, the cement is one of the most energy intensive materials.

The use of pozzolans and slags as replacement of cement in concrete, not only contributes

to the energy conservation but also helps in the solution of disposal problem of the by-

product materials.

The various types and varieties of SCMs such as condensed silica fume, fly ash, blast

furnace slag have been used as mineral admixtures in improving the properties of mortar

and concrete for many decades. The use of SCMs in concrete is not without problems.

When used in appropriate amount, some SCMs may be extremely effective, while others

may even cause more problems than in the absence of supplementary cementing material.

Moreover, the uniformity of these materials in some instances may be questionable.

Metakaolin, one of the natural pozzolans, is a nearly anhydrous solid obtained by

calcining kaolinite (commercially called China Clay) clay at a specific range of

temperature. An important feature of its dehydroxylation is that metakaolin retains a

CHAPTER-1 INTRODUCTION

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structural relation to that of its parent. Chemically, metakaolin combines with calcium

hydroxide to form secondary calcium-silicate and calcium aluminate hydrates. The

deposits of kaolin are located around the world; however, they vary in their chemical

composition at different sources. The calcination temperature and duration varies for

different deposits of kaolin. The chemical composition of the calcinated kaolin affects the

strength and durability and hence serviceability of structures when used as a pozzolan by

replacing part of it with ordinary Portland cement. Metakaolin is commercially prepared

in United States under the brand name of Power Pozz. A lot of research is also in progress

in Germany, Thailand, Greece and other parts of the world for the use of metakaolin as a

pozzolanic material.

The valuable types of kaolinitic clays occur in many parts of the world, i.e. North and

Central America, Hawaii, Caribbean region, Thailand and Pakistan. The term “Kaolin” is

now used variously to mean a clay-mineral group, a rock (consisting of more than one

mineral), and an industrial mineral commodity and interchangeably with the term “China

clay”. The following definition of kaolin by Ross and Kerr (1931) is probably the most

widely accepted one: “the rock mass which is composed essentially of a clay material that

is low in iron and usually white or nearly white in color”. The kaolin forming clays are

hydrous aluminum silicates of approximately the composition 2H2O.Al2O3.2SiO2, and it

is believed that other bases if present represent impurities or adsorbed materials. Kaolinite

is the mineral that characterizes most kaolins, but it and the other kaolin minerals may

also occur to a greater or lesser extent in clays and other rocks that are too heterogeneous

to be called kaolin.”

The microstructure of kaolin was studied by Silva and Glasser (1992). They found that

metakaolin was a nearly anhydrous solid obtained by heating kaolin in the temperature

range 450-800°C. They also suggested that calcination temperature within the range of

700-800°C is best for pozzolanic activation of kaolin clay.

Investigation on locally available kaolin in Thailand has been carried out by Sayamipuk

(2000) at AIT. He investigated the chemical and mechanical properties of metakolin

when used as pozzolanic material with concrete. The dosage of metakaolin, required to

get the optimum compressive strength of metakaolin concrete, was determined. Tahir’s

model (1998) was applied to predict the concrete strength at specified age.


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Poon et. al. (2003), investigated the behavior of metakaolin concrete at elevated

temperature up to 800°C. Eight normal and high strength concrete mixtures, incorporating

0%, 5%, 10% and 20% metakaolin concrete, were prepared. It was found that after an

increase in compressive strength at 200°C, the metakaolin concrete suffered a more

severe loss of compressive strength and permeability related durability than the

corresponding silica fumes, fly ash and OPC concretes at higher temperatures.

Batis et. al. (2004), studied the influence of metakaolin on corrosion behavior of cement

mortars at National University of Athens. He used a source of poor Greek kaolin having

very low kaolinite content. He also converted it to fine powder after thermal activation.

In addition, a commercial metakaolin of high purity was used. Several mixture

proportions were used to produce mortar specimens, where metakaolin replaced either

sand or cement. Mortar specimens were then exposed to the corrosive environment of

either partial or total immersion in 3.5% NaCl solution. For the evaluation of the

performance of metakaolin compressive strength, corrosion potential, mass loss,

electrochemical measurements of the corrosion rate by the Linear Polarization method,

carbonation depth and porosity were determined. It is concluded that metakaolin

improved the compressive strength and the 10% addition showed the optimum

contribution to the strength development. In addition, the use of metakaolin, either as a

sand replacement up to 20%, or as a cement replacement up to 10%, improves the

corrosion behavior of mortar specimens, whereas when added in greater percentages, it

does not produce any positive effect.

Tsivilis et. al. (2005), studied the use of Greek kaolin for use in concrete and investigated

the strength and durability aspects of concrete in comparison with controlled specimen of

commercially prepared metakaolin. The properties and the hydration procedure of

cements containing metakaolin were monitored for periods up to 180 days. Four

metakaolins, derived from poor Greek kaolins, as well as a commercial metakaolin of

high purity were used. Cement mortars and pastes, with 0%, 10% and 20% replacement

of cement with the above metakaolins, were examined. The strength development, water

demand and setting time were determined in all samples. In addition, XRD and TGA

were applied in order to study the nature of hydration products and the hydration rate in

the cement–metakaolin pastes. It was concluded that metakaolin had a very positive effect


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on the cement strength after two days and specifically at 28 and 180 days. The blended

cements demanded significantly more water than the relatively pure cement and greater

the quantity of metakaolin content, the higher in increase in water demand. The produced

metakaolins as well as the commercial one gave similar hydration products after 28 days

and the pozzolanic reaction was accelerated between 7 and 28 days, accompanied by a

steep decrease of Ca(OH)2 content. Finally, it was concluded that a 10% metakaolin

content seemed to be, generally, more favorable than 20%. The produced metakaolins,

derived from poor Greek kaolins, as well as the commercial one imparted similar

properties with respect to the cement strength development, setting and the hydration

Metakaolin can potentially be used as a major component in energy-saving binders. In

Pakistan, the china clay deposits are located in Swat in the North West Frontier Province

and at Nagar Parkar in the Sindh Province. These deposits have been used by the

ceramics industries of Pakistan but have never been explored as a pozzolon by the

construction industry of the country.

The use of metakaolin will revolutionize the construction industry of Pakistan. Its

remarkably high compressive and flexural strengths will make it economical for use in

high strength and light weight concrete. It is expected that its inclusion in concrete will

reduce the permeability and efflorescence and increase the resistance to chemical attack

and alkali silica reaction.

1.2 STATEMENT OF PROBLEM

Pakistan belongs to the list of under developed countries. The financial issues for such

countries are very important. Industry is the back bone of such countries; in a sense that,

they cannot be developed every day. Pakistan has different types of industries including

acid industry, acid based industries, fruits and beverages industries etc. Since concrete is a

common and cheapest material of construction which is used in nearly all types of

structures in Pakistan, acid or acid based industries are allergic to concrete. Whenever

acid is in contact with concrete, it destroys the concrete depending on the strength of acid

used in the process. Therefore, it is a matter of routine that these industries are always

undergoing repair for damaged concrete portions. Similarly, the fruits/vegetables which

are used in the development of prickle and various beverages are commonly mixed with

low concentration of acetic acid during production. Therefore the concrete or the


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production units are constantly exposed to such acids. The degrading reaction of acetic

acid with concrete results in maintenance of such structures.

Underground concrete structures, located in water saline areas are constantly exposed to

low concentration of sulfuric acid which is formed due to reactions with the sulphate salts

present in soil and also due to decomposition of plant decay. The stability of such

structures comes into question specially when the concrete cover is removed due to acid

attack and reinforcement is exposed to acid.

Acid attack on concrete depends on many factors. The most common among them are:

permeability, porosity, water-binder ratio, cement content etc. It is a universal saying that

a good quality concrete is a durable one as well. Although it is true in many senses;

however, considering the chemical properties of various supplementary materials, there

are some chemicals which improve the durability of concrete. For e.g. Sulphate resisting

cement is designed to resist the sulphate attack on concrete which is otherwise not

possible in case of ordinary Portland cement.

Carbonation is a very common phenomenon which results in the corrosion of steel

embedded inside the concrete for structures exposed to atmospheric conditions like

highway bridges, exterior of buildings etc. Carbonation depends on the quality of

concrete and the relative humidity. The quality of concrete is improved if packing of

concrete matrix is improved.

Kaolin clay is available in abundance in Pakistan but it is never explored to be used in

construction industry of Pakistan. The significance of metakaolin is very well known

from the literature review that it improves the compressive strength of concrete, acid

resistance of concrete, reduces sulphate expansion and carbonation etc. Since metakaolin

was never prepared from Kaolin deposits available in Pakistan other than their use in the

pottery industry of Pakistan, therefore, this research was focused to explore the new

construction material for Pakistan.

1.3 OBJECTIVE OF STUDY

The objective of the study was to develop a model for strength degradation of metakaolin

and control concrete. This study also included the development of chart for carbonation


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which can be used as a reference to obtain a fair estimate of carbonation depth. The

following sub tasks were carried out to achieve the main objective:

• Development of metakaolin and its optimization.

• To develop the strength degradation model by incorporating the chemistry

of cement and metakaolin which will include the casting of mixtures with

variable metakaolin-binder and water-binder ratios. The cubes developed

from these mixtures will be exposed to variable concentrations of a strong

and weak acid.

• To develop charts for carbonation depth of concrete. These charts will be

developed by determining the carbonation depths from concrete cubes

with variable metakaolin-binder and water-binder ratios. The concrete

cubes will be exposed to open atmosphere and carbonation depths will be

recorded at various time intervals.

1.4 SCOPE OF STUDY

The experimental program consists mainly of three phases:

1. Development of metakaolin

2. Experimental program for strength degradation and carbonation of control and

metakaolin concrete.

3. Development of strength degradation model for concrete cubes exposed to acids

and charts for carbonation samples.

1.4.1 Development of metakaolin

Raw kaolin is available in Nagar Parkar which is located in Sindh (Province of Pakistan).

This raw kaolin will be processed to produce metakaolin. The produced metakaolin will

be tested according to respective ASTM standards for new supplementary cementing

materials for its qualification.

The following experimental program will be followed for the production of metakaolin.


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Table 1.1 Experimental program for production of metakaolin

Mixture ID Heating Temperature(°C) Heating Duration (Hours)

A, B 0 0

C,D 600 6,8

E,F,G 700 6,8,10

H,I,J 800 6,8,10

K,L,M 900 6,8,10

N,O 1000 6,8

The above table shows the mixture ID based on temperature. The kaolin clay calcined at

different temperatures will be used to prepare the mortar mixture as per ASTM Standard

and then corresponding 7 and 28 days compressive strength of mortars will give the

optimum temperature for the production of metakaolin.

The metakaolin used in above experimentation will be finely grinded to Blaine’s value

higher than cement, in order to act as filler material as well. Mixture ID, “A” and “B” will

be used as control mixture to study the effect of metakaolin as filler material in cement.

1.4.2 Experimental program for strength degradation of control and metakaolin concrete and for carbonation

This is a huge experimental program. The main features of this experimental program

include two type of cement contents 300kg/m3 and 400 Kg/m3. There will be only one

type of metakaolin which is developed from kaolin clay of Nagar Parkar and one type of

cement which is ordinary Portland cement. Three replacement levels of 15%, 20% and

25% will be used along with the control mixtures. For each replacement level three water-

binder ratio of 0.45, 0.55 and 0.65 will be used. There will be twenty four mixtures in all,

out of which six mixtures will be used as the control. The remaining eighteen mixtures

will be having different mixture proportions.


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The tabular form of these mixtures detail is given as follows.

Table 1.2 Mixture details for strength degradation model and carbonation experimentation.

Cement Content (Kg/m3) Metakaoin-Binder ratio Water-Binder ratio

300

0

15

20

25

0.45, 0.55 &0.65

0.45, 0.55 &0.65

0.45, 0.55 &0.65

0.45, 0.55 &0.65

400

0

15

20

25

0.45, 0.55 &0.65

0.45, 0.55 &0.65

0.45, 0.55 &0.65

0.45, 0.55 &0.65

Table 1.1 shows the main mixtures for the experimentation program. For example the

cement content 300 Kg/m3 has four different metakaolin to binder ratios and for each

metakaolin binder ratios there are three different water-binder ratios. This combination

will give three different mixtures and hence binder content 300 Kg/m3 as a whole will

yield twelve different mixtures.

100mm cubes prepared from each mixture will be subjected to two different types of

acids i.e. sulfuric and acetic acid. The cubes shall be exposed to acid solution of different

strength after twenty eight days of curing. Three concentrations of sulfuric acid and three

for acetic acid will be used in the experimental program which is 2%, 5% and 8%. The

details are given in table 1.3.


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Table 1.3 Exposure of concrete cubes to sulfuric and acetic acid.

Cement Content (Kg/m3)

Metakaolin-Binder ratio

Water-Binder ratio

Sulfuric/Acetic Acid Exposure (%)

(For each MK-Binder ratio)

300

0

15

20

25

0.45, 0.55 &0.65

0.45, 0.55 &0.65

0.45, 0.55 &0.65

0.45, 0.55 &0.65

0.45----2,5,8

0.55----2,5,8

0.65----2,5,8

400

0

15

20

25

0.45, 0.55 &0.65

0.45, 0.55 &0.65

0.45, 0.55 &0.65

0.45, 0.55 &0.65

0.45----2,5,8

0.55----2,5,8

0.65----2,5,8

For example the cement content 300 Kg/m3 has four different metakaolin-binder ratios

and for each metakaolin binder ratios there are three water-binder ratios and concrete

cubes for each metakaolin-binder (say 0.15) and water-binder ratio ( say 0.45) will be

immersed in acid concentrations of 2,5 & 8% for both sulfuric and acetic acid.

100mm cubes will also be used for the carbonation determination. The mixture details for

the carbonation specimen are same as that specified in table 1.2. Carbonation specimens

will be directly transferred to the open atmosphere after twenty eight days of curing.

1.4.3 Development of strength degradation model for concrete cubes exposed to acids and charts for carbonation samples.

The experimental program given in section 1.4.2 consists of two thousand eight hundred

and eighty concrete cubes. Each mixture consist of one hundred and twenty cubes

inclusive of extra specimens. One hundred and five cubes are reserved for compressive

strength and acid exposure and remaining fifteen are reserved for carbonation.

The compressive strength of the cubes for each mixture will be determined at 7 and 28

days. The cubes will be immersed in acid bath of different strengths after twenty eight


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days of curing. The degraded compressive strength of concrete cubes will be determined

at 7, 28, 91 and 182 days of immersion period. Once all the data is completed then

strength degradation model will be developed.

The carbonation samples will be transferred to open atmosphere after twenty eight days

of curing. Carbonation depth will be recorded at an interval of 4, 7, 13, 25 and 52 weeks

interval. Finally the carbonation depths will be graphically plotted for all twenty four

mixtures to provide a quick reference for determination of carbonation depth for a

comparable mixture.

CHAPTER-2

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LITERATURE REVIEW 2.1 INTRODUCTION

This chapter discusses review of literature on the properties and durability of mortar and

concrete. Pozzolan and their effective use in mortars and concrete are much diversified.

However there are basic parameters for the different type of pozzolans which are helpful

to improve the quality of concrete and mortars. These parameters are discussed in detail.

In this chapter alkali silica reaction, Sulphate resistance, permeability, acid attack, freeze-

thaw resistance etc are discussed in detail along with the basics of cement and pozzolans.

2.2 POZZOLAN

According to Lea (1988), the word pozzolan has been divided into two portions. First

portion indicates the pyroclastic rock also termed as zeolites which was available in

Rome. Second portion includes inorganic material which may be artificial or natural. This

material when reacts with calcium hydroxide, attains hardness. ASTM 618-01 states that

when pozzolan is used inside the concrete or mortar, it reacts with silica present inside the

pozzolan and reacts with the lime which is available due to the hydration reactions of

tricalcium silicate and dicalcium silicate which are the main compounds of Portland

cement.

Pozzolanic materials are therefore defined with respect to their use as cementitious

material instead of chemical and physical phenomena by the virtue of which it hardens.

There are lots of pozzolanic materials which are available in the world today. These

materials differ entirely in their composition, mineralogical constitution, origin etc. Lea

(1988) divided the pozzolans into two main groups natural and artificial materials.

Natural materials do not require any treatment for their use as pozzolans other than

grinding to increase the surface area. However, the artificial materials are produced by

improving the properties of weak pozzolans.

Natural pozzolans include the materials of volcanic origin, compact materials (Tuffs) and

materials of sedimentary origin. Pyroclastic rocks originate from explosive eruptions of

volcanoes which results in dispersion of minute particles of melted magma into the

atmosphere, the gases evolves into the air and resulting into pozzolan having micro

CHAPTER-2 LITERATURE REVIEW

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porous structure (Penta,1954). Volcanic pozzolan which gets deposited and later on

exposed due to weathering action is called compact materials or tuffs. Weathering cause

either zeolitisation (Conversion into zeolite which is a natural or synthetic hydrated

alumino-silicate with an open three-dimensional crystal structure, in which water

molecules are held in cavities in the lattice) or argillation (weathering of aluminum

silicates) which turns the glass of pozzolan either into zeolitic minerals or clay minerals.

This phenomenon depends on intensity of chemical and physical changes to the deposits

as well as their duration. Zeolitisation improves the pozzolanic activity while argillation

reduces it (Sersal, 1958) & Malquori (1962).

Pozzolan from sedimentary rocks are also called diatomaceous earth. They can combine

with lime giving calcium silicate and aluminate hydrates (Eades, 1960). Diatomaceous

earths are very reactive and combine with lime due to presence of silica. The only

problem exists with these earthy materials that their surface area is more and they

increase the water demand of the system. Turriziani & Corradini (1961) studied the

earth’s from mixed origins and found that upper layers in this type of rocks show silica

content up to 90%. However it is much less in the deeper layers. Similarly, other oxides

are also having a lesser percentage.

The second type of pozzolans are artificial pozzolans which include clay, shale, certain

siliceous rocks, fly ash, silica fume, rice husk ash and granulated blast furnace slag etc.

Fly ash is collected from power stations using special mechanical devices. It is produced

during the burning process of pulverized coal. Their chemical composition is dependent

on the mineral composition of the coal. Clay minerals composed of silica and alumina

and they are obtained mainly by calcination of clays between 600-900ºC. The use of clays

for binding action was common since ancient times. Chemical composition of clays

depends on the source of origin. Silica fume or micro-silica is obtained during the

manufacturing process of Silicon metal in which fumes are generated during the process

when the temperature rises to 2000ºC. These fumes contain spherical micro particles of

amorphous silicon dioxide. It is also called as volatized Silica (Sellevod & Nilsen, 1987).

The important features of silica fume are surface area and very high silica content which

make it very prominent among the pozzolans. Other pozzolanic material like rice husk


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ash also contains 80% silica whose pozzolanic activity is dependent on the burning

temperature and retention period (Cook & Suwanvitaya, 1983).

2.3 POZZOLANIC REACTION

The measure of pozzolanic reaction is the amount of minimum free lime present in the

system or increase in silica and alumina content soluble by the acids (Vittori & Cereseto,

1935). Pozzolanic activity involves two parameters, maximum amount of free lime to be

dissolved and rate at which the reaction occurs. These parameters are further dependent

on quality and quantity of active phases. It is generally agreed that consumption of free

lime depends on nature of active phases, silica content, pozzolanic ratio of the mix, length

of curing. The chemical process involving the consumption of free lime is further

dependent on surface area of the pozzolan, water/solid mix ratio and temperature.

Takemoto & Uchikawa (1980) showed that the short term pozzolanic activity depends on

the surface area of pozzolans. However, long term activity is dependent on the chemical

and mineralogical composition of pozzolans and found to be square of the specific

surface area.

During thermal treatment, many pozzolans undergo chemical and structural changes both

on positive or negative side. The positive aspects include the cover of loss of water in

zeolitic phases and destruction of crystal structure in clay minerals while the negative

impact is conversion of glassy texture into crystal texture. These changes are dependent

on the nature of the pozzolans, heating temperature and duration of heating. Different

type of pozzolans has different optimum temperatures for the formation of more stable

phases (Costa and Massazza, 1977).

The reaction of pozzolans produces the same compounds as obtained during the hydration

of the cements. The nature of reaction remains the same however, the quantity of

compounds varies but the difference is very minor. Natural pozzolans when reacting with

lime form calcium silicate hydrate (C-S-H) and hexagonal aluminates (C4AH13) (Ludwig

& Schwiete, 1963). Fly ashes containing high content of lime may have variable amounts

of free lime which on reaction transform into calcium hydroxide and finally hardens

without the addition of further lime (Massazza & Cannas, 1962). In case of burned kaolin

(Metakaolin) the reactive compounds are mainly calcium silicate hydrate (C-S-H),


14

gehlenite hydrate (C2ASH8) and small quantities of calcium aluminate hydrate (C4AH13)

i.e. almost the same as in the case of the natural pozzolans (Murat, 1983).

2.4 METAKAOLIN (STRUCTURE AND DEVELOPMENT)

Kaolin clay occurs in many parts of the world generally occurring in North and Central

America, Hawaii Islands, Caribbean region, Thailand and Pakistan. Ross and Kerr (1931)

described the kaolin as the rock mass of clay origin, low in iron and usually white or

nearly white in color. Clays forming kaolin are hydrous aluminum silicates of

approximately the composition 2H2O.Al2O3.2SiO2, and it is believed that other bases if

present represent impurities or adsorbed materials. Kaolinite is the mineral that

characterizes most kaolins, but it and the other kaolin minerals may also occur to a greater

or lesser extent in clays and other rocks that are too heterogeneous to be called kaolin.

Kaolin clay is also termed as “China Clay” and used mainly in ceramics industry, and to a

lesser extent, in paper, paint, refractory, and insecticide industries.

Silva and Glasser (1992) studied the microstructure of kaolin and found that it is

anhydrous solid obtained by heating kaolin in the temperature range of 450-800ºC.

During dehydroxilation metakaolin contain its parent structural relation. Generally

calcination of kaolin within the range of 700-800ºC gives the best activation. It also

contains other alkali compounds which are responsible for set properties similar to that of

the Portland cement.

He et al. (1995) studied the X-ray diffraction background and alkali-soluble Si of

pozzolanic clays, reflecting the thermal decomposition and pozzolanic activity of these

materials. He did not consider the particle size effect during the strength development for

different types of clays. He took three different samples of untreated clays which were

Ca-montmorillonite (+amorphous SiO2) > illite > kaolinite > Na-montmorillonite >

mixed-layer clays > sepiolite . In order to increase the pozzolanic activity he found that

maximum activity for Ca-montmorillonite, Kaolinite, Kaolinite and for mixed-layer clay

were found to be at 830°C, 650°, 830°C and 960°C respectively. The compressive

strength (28 days at w/b of 0.40) of these clay-cement mortars are 112-130% of plain

ordinary Portland cement mortar. Illite and sepiolite mortars lie at about 80-84% of the

OPC strength even at the optimum calcination temperatures.


15

Coleman & Mcwhinnie (2000) studied the chemistry of metakaolin blended ordinary

Portland cements using differential thermal analysis (DTA) and solid state magic angle

spinning nuclear magnetic resonance spectroscopy (MAS NMR). They found that

hydrated gehlenite and a relative reduction in calcium hydroxide content of the

metakaolin blended OPC paste which is the sign of pozzolanic activity of metakaolin. It

was also reported that the primary reactive of the centre of pozzolans are Alumina and

amorphous silica.

Kaolinite is a phyllosilicate, i.e. a layer silicate. Every crystal flake is composed of a

stacked arrangement of layers. The study of the individual layer defines the mineral.

Every layer is an association of two different sheets, named the tetrahedral sheet and the

octahedral sheet. The tetrahedral sheet is so called because it is formed by the association

of a tetrahedral arrangement in a plane. The four tips of the tetrahedral are occupied by

oxygen ions and their center by a silicon ion which shares its four positive changes with

the four oxygen ions of the tips. The octahedral sheet is composed of an octahedral

arrangement in a plane. The six tips of the octahedral plane are occupied by oxygen ions

of hydroxyl groups and their center by an alumina octahedral sheet form one layer of

kaolinite. The structural formula of kaolinite is Al2Si2O5(OH)4 (Gruner, 1932, Brindley

and Robinson, 1946).

The main sources of kaolin in Pakistan are in Swat Region and Nagar-parkar, Sindh. The

two regions are shown in the figure- 2.1

Kaolin deposits, which are available in Pakistan are mainly sedimentary in origin. These

are pre-dominantly flood plain deposits. The deposits present in the Northern area

contain greater extent of impurities, however, deposits present in the South of Pakistan (

Nagar-Parkar, Sindh) are of good quality. Kaolin is obtained in the forms of lumps from

its origin. These lumps are calcined in a temperature range of 600-800ºC in order to

enhance their pozzolanic activity. After calcination, the kaolin clay is called metakaolin.

Calcination imparts hardness to the clays. These clays are then grinded to increase the

surface area of pozzolan which is directly linked with the pozzolanic activity (Takemoto

& Uchikawa ,1980).

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17

clays or shales are used, they requires long heating durations for a temperature range

between 500-1000ºC. Although it has been established earlier that parent materials inside

the clay control the properties of the pozzolanic material (Costa and Massazza, 1977).

The temperatures for maximum activity for the three main groups of clay minerals,

montmorillonite, kaolinite, and illite were respectively 600-800°C; 700-800°C and 900-

1,000°C. At these temperature ranges, the chemically bonded hydroxyls were lost

resulting in the collapse of the structure, consequently a large amount of free surfaces

were released for the reaction.

Badogiannis et al., (2005) effectively carried out the optimization of Greek kaolin with

different alunite content. Samples were heated at different temperatures during different

times. Effect of calcination was studied by DTA-TG and XRD analysis of the raw and

thermally treated kaolin by pozzolanic activity analysis of metakaolin and finally by

strength development analysis of cement metakaolin mixtures. It was found that heating

at 650ºC for 3 hours is efficient to convert poor kaolins with low alunite content to highly

reactive metakaolin. However kaolin with high alunite content requires thermal treatment

at 850ºC for 3 hours in order to remove undesirable Sulphur trioxide.

The above discussion strongly validates that calcination of clays within the range of 600-

1000ºC converts into the pozzolans. The duration and temperature of heating depends on

the source of origin of clays and found to be different for clays from different origins.

Due to the replacement of cement with the pozzolans, heat of hydration is also reduced

with the reduction in the quantity of cement and it also reduces the formation of calcium

hydroxide which is a soluble compound.

2.5 STRENGTH

Strength is the main parameter of concrete. Increased strength shows good packing of

materials, higher densities and therefore good performance of concrete. A lot of work has

been done in the past regarding the use of pozzolan to increase the strength and durability

of concrete. The following paragraphs will discuss the role of metakaolin in the

enhancement of concrete strengths.

Ambroise et al. (1985) studies the improvements in the strength of metakaolinite cements

activated with calcium hydroxide. They found that the more convenient curing process


18

implied the immersion in water after the removal of samples from the molds at 7 days,

and drying at 50°C for one day before mechanical testing. The process leads to

considerable improvement of strengths, which was due to an increase of CSH formation

rate in the material. For pure metakaolonite, another strength improvement can be

obtained by a sensible choice of the metakaolonite/calcium hydroxide ratio which must be

higher than unity (MK/CH = 3). The replacement of calcium hydroxide by pure calcite or

gypsum was without any interest : metakaolinite is not hydrated at 28 days. Kostuch et

al. (1993) produced the metakaolin and mixed with the cement on the basis of equivalent

calcium hydroxide. They found that there is no negative effect on the strength of concrete.

Moreover it prevented the alkali silica reaction, increased permeability, made concrete

more acid resistant and does not em-brittle alkali resistant glass fiber used in GRC.

Caldarone et al. (1994) found that inclusion of metakaolin is not detrimental to the

air void system of concrete. Measurement of the hardened air content showed that the 10

percent metakaolin concrete was less dense and contained more air voids in comparison

to that of concrete containing 10 percent of silica fume but the strength of metakaolin

concrete is equal or more than that of concrete containing silica fume. Metakaolin also

reduces the chlorides permeability in metakaolin concrete in comparison to control

mixture. Zhang and Malhotra (1995) studied the various properties of metakaolin by

incorporating with OPC. They found that concrete having 10% replacement level of

metakaolin has higher compressive strengths up to 180 days for all the ages in

comparison to that of control concrete. Metakaolin concrete has also shown good tensile

strength than that of control and concrete containing silica fume. It also showed good

performance in freezing and thawing test. In case of de-icing salt scaling, it gave results

similar to that of concrete with silica fume, however, slightly on lower side than that of

control concrete.

Replacement level of metakaolin shall be more than 15 percent has been shown by (Wild

and Khatib, 1996). He proved this by observing the calcium hydroxide in the paste over a

year. He found that CH contents of both metakaolin mortar pastes and their equivalent

standard pastes show a minimum at about 14 days which coincides with a maximum in

relative strength. This is attributed to a peak in pozzolanic activity for which more CH is

being removed from the paste than is being generated by cement hydration. Reaction of


19

metakaolin with lime between 14 and 28 days appears to severely retarded due to increase

in CH. This retardation can be explained in terms of formation of an inhibiting layer of

reaction product on the metakaolin particles. Beyond 28 days there is evidence of further

secondary reaction of metakaolin with CH, particularly for the aggregate free pastes;

although, this is not reflected in any additional enhancement of relative strength. This

suggests that replacement levels considerably in excess of 15% would be required to fully

consume all the CH.

Wild et al. (1996) identified three elementary factors which influence the contribution

that metakaolin concrete strength. These are the filler effects, which are immediate, the

accelaeration of PC hydration, which occurs within the first 24 hours and the pozzolanic

reaction, which has its maximum effect within the first 7-14 days for all metakaolin

replacement levels between 5-30%.

Sabir (1998) studied the effect of curing temperature on strength development in

concretes containing up to 15% metakaolin replacement level. He found that curing of

metakaolin concrete at 50ºC results in increased early strength (7 days) compared to the

strength of specimens cured at 20ºC. The acceleration in strength development due to

high curing temperature diminished in the long term(365 days). The strength of the

metakaolin concrete when compared with the control concrete at 20ºC was found to be

10% with water to binder ratio of 0.35. However this replacement level decreases to 5%

at higher temperature with higher water to binder ratio of 0.45.

Sabir et al. (2001) carried out the review regarding the use of calcined clays and

metakaolin as a pozzolan for concretes. They found that the use of metakaolin as partial

cement replacement material in mortar and concrete has been studied widely in recent

years. The work reviewed demonstrates clearly that MK is a very effective pozzolan and

results in enhanced early strength with no detriment to and some improvement in the long

term strength.

Li and Ding (2003) investigated the physical and mechanical properties of Portland

cement containing metakaolin or combination of metakaolin and slag. They observed an

increase in the compressive strength when metakaolin (10%) is incorporated in the OPC.

However, the fluidity of the mix decreases for the same dosage and water to binder ratio


20

of control mix. When metakaolin is used in combination with slag (20-30%) then fluidity

and compressive strength both increases.

Poon et al. (2006) studied the mechanical and durability properties of high performance

metakaolin (MK) concrete an silica fume concretes and found that the performance of the

MK used in this study was superior to the silica fume in terms of strength development of

concrete. But the performance of MK was similar to silica fume in terms of the chloride

resistance of concretes. He also observed that MK concretes prepared at W/B ration of 0.5

showed higher compressive strength increases at early ages than at a W/B ratio of 0.3,

when compared with control concrete.

2.6 PERMEABILITY

Concrete is used in super as well as sub structures. Concrete stays at its place and faces

the harsh environment. The process of resisting the environmental conditions surrounding

the concrete in order to remain in its original configuration is called the durability of the

concrete or measure of its durability. There are various phenomena which affect the

durability of concrete.

Permeability is one of the important properties of concrete which determines the

durability of concrete (Cabrera and Lynsdale, 1988). The discussion made below will

restrict to the use of metakaolin in case of permeability improvement, as explored by the

other researchers.

Diffusion, permeation, capillary suction, adsorption, desorption and migration are the

different transport mechanism in concrete which differs from that of permeability.

Diffusion is the transfer of mass by random motion of free molecules. Permeation is the

flow of liquids or gases caused by a pressure head. Capillary suction is the transport of

the liquids in porous material due to surface tension acting in capillaries (Martys and

Ferraris, 1997). Absorption is the fixation of molecules on solid surfaces due to mass

forces in mono or multi molecular layers and desorption is the liberation of absorbed

molecules from solid surface. Migration is the transport of ions in electrolytes due to the

action of an electric field as the driving force.

Baker (1983) found that there is a direct link of curing temperature and permeability of

concrete. In his investigation he proved that permeability of OPC at higher curing


21

temperatures increases whereas it decreases for blended cements. This has been explained

by a weak dispersion of the precipitated hydration products of the clinker at higher

temperatures. It is unlikely that the hydration products of OPC at higher temperatures are

precipitated closer to the reacting gains because of faster reaction and precipitation.

Mehta (1987) found that permeability increases in concretes having larger aggregate

sizes; although, the volume fraction of paste decreases.

The imperfect packing of different particles in concrete matrix may result in

concentrations of cement mortars in certain regions especially at the surface of the

concrete which may result into different permeability for surface layers then that of the

body of the concrete. In a similar way, the packing of cement grains within the paste

fraction is also disrupted by the presence of aggregate surfaces (Scrivener and Gartner,

1988).

Ollivier et al. (1995) described the concrete as porous material, and permeability in

concrete as a function of size distribution and connectivity of pores. He also mentioned

the factors influencing the permeability of ordinary Portland cement concrete as water to

cement ratio, age, curing, aggregate type, entrained air and additions.

The discussion mentioned above, strongly revolves around the packing of the concrete

matrix or more precisely the pore refinement. Permeability depends on the packing of the

material. Supplementary cementing materials having size less than that of cement can

improve the permeability of concrete matrix. Swamy and Darwish (1997) studied the

effectiveness of mineral admixtures and curing regime on air permeability of concrete and

found that cement replacement plays vital role in improving the air permeability at an

early age and continue to posses the property with time. However, mixtures with large

replacement require long curing period in order to develop the air permeability of the

same level as that for control concrete. Naik et al. (1994) studied the effect of

compressive strength on the permeability of concrete and found that it increases with

increase in the compressive strength but it is very difficult to correlate the results and

develop a suitable relationship.

According to Sabir et al. (2001) the use of metakaolin improves the micro-structure and

observed significant changes when cement is replace by 20% of metakaolin. It also


22

reduces the rate of diffusion of Cl- and Na+ ion in mortars and water absorption. The pore

structure of cement paste contain 15% metakaolin was also examined using mercury

intrusion. The test revealed that the proportion of pores of radii <0.02 µm within the paste

increases with an increase in both metakaolin content and curing time. The refinement of

pore was found to be very rapid up to 14 days cruing after which pore size changed very

little.

Khatib and Clay (2004) studied absorption characteristics of metakaolin concrete. During

the test they found water present at the top of surface of the sample for the control mix,

although the top surface was not in contact with the water. However in-case samples

containing 15% and 20% metakaolin, there was no water at the top surface of the

samples. They termed it as pore blocking effect and found discontinuity of pores when

the cement is partially replaced with metakaolin.

2.7 RESISTANCE TO ACID ATTACK

Acids are damaging to concrete. In case of acid attack there are no complex reactions

generated as the case for sulfate attack. However, in case of acid attacks soluble

compounds are dissolved which destroys the crystalline structure and leaving behind only

incoherent residue. The attack increases with an increase in pH values which is

logarithmic function of the hydrogen ion. The rate of attack also depends on the rate of

diffusion of hydrogen ions through the cement gel (C-S-H) after calcium hydroxide has

been dissolved and leached out.(Lea, 1988).

Fattuhi and Hughes (1988) determined the performance of cement paste subjected to

sulphuric acid. According to them sulphuric acid largely occurs in industrial

environments. However, random spillage, unscheduled washing down, leakages,

irresponsible dumping of chemical waste are the main sources of severe sulphuric acid

attacks. In natural ground water sulphuric acid is likely to be found as a result to the

oxidation of sulphuric minerals such as pyrites and marcasiste, a process which is

catalyzed by the presence of aerobic bacterium, thiobacillus ferro-oxidans. During

exposure of concrete to sulphuric acid or acidic water, the calcium hydroxide reacts with

the sulphuric acid to form gypsum, which can be readily washed away.


23

Grube and Rochenberg (1989) studied the durability of concrete structures in acidic water

and they also proposed the mechanism of acid attack in which carbon dioxide dissolved in

water first forming a thin layer of calcium carbonate very close to the surface in the paste.

Additional carbon dioxide leads to the formation of calcium bicarbonate which is soluble

in water. The same process happens in case of calcium, forming calcium silicates which

are again soluble. Hydrous silicon dioxide gel layer remains also containing aluminum

and iron. This layer becomes thicker with the increase in level of attack and due to the

weak interaction of paste with the aggregates, aggregates come out of their place under

mechanical action. However, the rate of concrete removal does not increase if the

aggregate particles within the gel layer remain in place being held; for instance by the

surrounding soil.

Harrison (1987) concluded that there was a slower rate of acid attack on concrete with

reduced lime content. Hobbs and Matthews (1998) pointed out that the reduction in water

to cementitious ratio improves the acid resistance.

Ellis et al. (1991) studied the performance of concrete for its durability using fly ash and

metakaolin. He found that when these additives are used in concrete, it forms the

cementitious compounds (C-S-H) due to the chemical reaction of calcium hydroxide with

pozzolan during the hydration of cement. This resultant matrix is more chemically

resistant by virtue of its denser microscopic pore structure.

Hengsadeekul (1995) and Visessompak (1997) found that the resistance against sulfuric

acid of fly ash-OPC, rice husk ash-OPC and metakaolin-OPC mortars were significantly

higher than that of OPC mortars. The metakaolin-OPC mortars possessed the best

resistance among these three types of pozzolan-OPC mortars. For the resistance against

hydrochloric acid, fly ash-OPC and rice husk ash-OPC mortars showed similar results

with that of OPC mortars whereas metakaolin-OPC mortars possessed the poorest

resistance.

Roy et al. (2001) investigated the use of silica fume, metakaolin and low calcium fly ash

for their chemical resistance. He carried out the test for 1% and 5% solution strengths of

sulphuric, hydrochloric and nitric acids. He found that mortars were little affected by the

acid of 1% of solution strength. However at 5% of solution strength, it showed the poor


24

chemical resistance . In general, it was concluded that it is important to evaluate a

particular concrete formulation before predicting its performance in a special acid

environment. At least under certain circumstances the addition of fly ash, silica fume or

metakaolin can improve the acid resistance of concrete.

2.8 SHRINKAGE

Shrinkage in concrete is measured from concrete or mortar prisms that are allowed to dry

naturally in controlled humidity environment and shrinkage is measured by monitoring

changes in length using surface attached strain gauges or by recording length changes at

the axis of the prism. These days computers are connected for automatic reading of the

data (Lea, 1988).

The components of cements which most influence shrinkage are the alkalis, C3A and

sulfate, these parameters interact with the fineness of grinding of the cement (Lerch,

1946). Helmuth and Turk (1967) carried out the research on drying shrinkage of hardened

cement pastes and found that an increase in C3A or alkalis increases the first drying

shrinkage, while this increase can be nullified by adding calcium sulfate although excess

calcium sulfate can lead to a slight increase in shrinkage. He also found that pure alite and

C3S pastes behave similar to that of neat cement pastes.

Mullik (1972) studied the role of stress in maturing concrete considering the

microstructure and creep properties. He found that first drying shrinkage is approximately

proportional to the water cement ratio. He took mortar prisms and cured for 7 days. The

mortar prisms shrank more when the water cement ration was increased.

The reduction in shrinkage using pozzolans has been studied by many researchers. Ivan et

al. (1969) used fly ash to reduce the autogenous shrinkage in concrete for Dworshak

Dam. He found that concrete mixtures with constant cement content (Portland cement

plus pozzolan by absolute volume), 30% fly ash replacement showed lowest autogenous

shrinkage over a three-year observation period. Highest autogenous shrinkage was shown

by concrete containing calcined shale, pumicite, opaline slag. Reduction of cement

content resulted in reduction in autogenous shrinkage regardless of pozzolan or storage

temperature used. Increase in storage temperature increased both the rate and magnitude

of autogenous shrinkage.


25

Mehta (1987) found that the drying shrinkage of products made with Portland-pozzolan

cements is generally higher than that of the corresponding product containing Portland

cement alone. This difference is to be expected because the drying shrinkage of a

hydrated cement paste is generally attributable to the content of CSH, which would be

relatively higher in the case of Portland-pozzolan cements. However, many researchers

have observed that the cracking tendency resulting from drying shrinkage in concretes

containing pozzolans is less than that in corresponding concretes without pozzolans. He

also explained the two explanations about the reasons behind the incidence of drying

shrinkage cracking in Portland-pozzolan cement products being lesser than expected.

First, it seems that the restraining effect of aggregate on the shrinkage of the cement paste

in mortar or concrete plays a more important part in determining the total amount of the

shrinkage. The second explanation for relatively less cracking in Portland-pozzolan

cement products lies probably in the stronger transition zone between the aggregate and

cement paste, compared to corresponding concrete without the pozzolan. Therefore, at a

given ratio of water to cementitious material, the flexural and tensile strengths of

Portland-pozzolan cement concrete tend to be higher than the Portland cement concrete.

This increases the tensile strain capacity and hence the crack resistance of the former

under given shrinkage conditions.

Fujiwara (1989) studied the relation between mix proportion and drying shrinkage of

hardened cement paste, mortar and concrete. It was obvious that the larger the water

content is, the larger will be drying shrinkage in the case of mix proportion of medium

and wet consistency. In order to prevent large drying shrinkage and the occurrence of

cracks, it was very important to decrease water-content, as much as possible, within the

range of these mix proportion. On the other hand, in spite of their small water content,

mix proportion with very stiff consistency showed shrinkage larger than expected. The

relation between paste content and drying shrinkage was pointed out for further

investigation. The larger the cement content , the larger the drying shrinkage, when

water-to-cement ratio was constant, except for a very lean mixture, which showed

comparatively large shrinkage.

Wild et al. (1998) studied the effect of metakaolin on creep and shrinkage of concrete and

proved that for metakaolin pastes (w/b ratio =0.55), autogenous shrinkage increased for


26

metakaolin content up to a maximum of 10% then, it appears to be comparable to that of

the control cement past for metakaolin content above 15% . An expansion up to 14 days

for all the compositions (0-25% MK) was also observed, except of 10% metakaolin.

Kinuthia et al. (2000) investigated the effect of fly-ash and metakaolin cement paste. He

found in cement MK pastes (w/b =0.5), that 5% and 10% metakaolin increased the

autogenous shrinkage of cement pastes while at 15% and 20% metakaolin, they observed

a significant decrease.

Gleize et al. (2007) carried out his studies on effect of metakaolin on autogenous

shrinkage of cement pastes. In his study four partial replacements levels (5%, 10%, 15%,

and 20%) were used. He concluded in his research that long term autogenous shrinkage of

cement metakaolin paste with w/b ratios of 0.3 and 0.5, decreases as the cement

replacement level by metakaolin is increased. No overall expansion of pastes was

observed at early ages. The apparent contradiction between the results of this study and

other found in literature might be partly examined by the differences in cement and

metakaolin compositions.

2.9 RESISTANCE TO ALKALI SILICA REACTION

Portland cement concretes are naturally alkaline because Portland cement reacts with

water to produce solutions which are saturated with calcium hydroxide, but sodium oxide

and potassium oxide are also present in Portland cement in small and variable percentages

as minor components. They form sodium hydroxide and potassium hydroxide solutions as

the cement aluminates and ferrite hydrate to absorb the sulfate ion. These highly alkaline

solutions are able to react with certain aggregates which contain a reactive form of silica,

to give a gel which is able to absorb water and swell, thus generating a pressure which

can crack the concrete. This phenomenon is called as alkali silica reaction or ASR (Lea,

1988).

Power and Steinour (1955) suggested that gel products that are low in calcium are

expansive, while gel products with high calcium content are not expansive or less

expansive. They explained the phenomena that when silica is initially attacked by OH-

ions; a calcium alkali- silica product is formed around the reacting aggregate. Further

attack of the intact silica inside the aggregate by calcium and alkali hydroxides from the

pore solution would continue by the diffusion of these hydroxides through the non


27

expansive calcium alkali silica layer. If the concentration of the alkali with respect to the

calcium ions in solutions is high, calcium ions will not reach the silica particles in the

interior of the aggregates fast enough and expansive gels will form. On the other hand, if

calcium ions reach the reacting silica fast enough, non expansive calcium alkali silica gels

will develop.

According to Mantuani (1983), he explained, the alkali-silica reaction which takes place

in the silica minerals or rocks produces relatively dry alkali-silica gel, absorbs free water

and swells generating hydrostatic expansive forces; the predominantly calcium alkali-

silica products are non-swelling if absorption theory is used.

Chatterji (1989) explained different theories regarding the ASR reactions. The main

points of which are delineated as follows:

1. The attack of OH- on silica grains is accompanied by the penetration of cations,

i.e. Na+, K+ and Ca++ to the reaction sites. However, more of the smaller ions,

i.e. Na+ and K+ will follow the penetration of OH- ions than the larger ions, i.e.

Ca++ although both types of cations will penetrate reactive silica grains.

2. Some molecules of silica will diffuse away from their original sites.

3. Site Ca++ ion concentration in the environment controls the rate at which silica

diffuses out of the grains. The higher the Ca++ concentration of the environment,

the lower the rate at which silica diffuses out of the grains and the higher the rate

at which cations diffuse into the grains.

4. Expansion occurs when the amount of material entering a grain, i.e. Na+, Ca++,

OH- and water, exceeds the amount leaving(i.e. silica).

Therefore, the Ca++ concentration in the environment controlled the relative rates

of diffusion into and out of the reactive grains.

Buttler (1988) documented that damage due to reaction could occur in any concrete

which has a combination of (a) a sufficiently high alkalinity (b) a critical amount of

reactive silica and (c) sufficient moisture to enable the reaction to proceed. If one of these

factors is removed the risk of this reaction causing damage to the concrete by expansion

is minimized.


28

Application of pozzolan as replacement material has also been found to be effective in

reducing the ASR reaction. Coleman and Page (1997) studied the replacement of cement

with metakaolin and found that it reduces the risk of expansion due to alkali-aggregate

reaction due to the drop in pH value of pore solutions. This improves the corrosion

resistance of steel embedded inside the concrete. They also found that significant

reductions in the pH value of the pore solution have been observed when 10 or 20 percent

of metakaolin is blended with OPC of moderate alkali content (0.63% equivalent Na2O).

Aquino (2001) studied the influence of metakaolin and silica fume on the chemistry of

alkali-silica reaction products and found that silica fume and high reactivity metakaolin

performed similarly in controlling expansion due to ASR in mortar bars. He also

concluded that calcium content of ASR products increased with time in all the specimens.

However, lower levels of calcium were detected in specimens containing mineral

admixtures.

2.10 RESISTANCE TO SULPHATE ATTACKS

Sulfates of various bases occur naturally and are also extensively used in industry. Their

solutions enter into the chemical reactions with compounds present in set cements,

causing expansion, cracking or spalling of the concrete or softening and disintegration.

Ordinary Portland cement is the most vulnerable to attack, but while sulfate resisting

Portland, pozzolanic and Portland blast furnace cements have greater resistance, they are

not immune to attack in all situations and at all concentrations of sulfate solutions. The

action of sulfates and the protection of concrete against their damaging effects are of

considerable concern. Calcium, magnesium, sodium and potassium sulfates are found

throughout the world in clays and other soils, frequently in good quantities. All soluble

sulfates have a deleterious action on Portland cement concrete, but the mechanism and

severity of attack vary according to the base present. Calcium sulfate is formed due to

reaction of sodium sulfate with free calcium hydroxide in the set cement to form calcium

sulfate, which then reacts with the aluminates. Magnesium sulfate has a more far reaching

action than other sulfates and decomposes the hydrated calcium silicates in addition to

reacting with the aluminates and calcium hydroxide (Lea, 1988).

Hooton (1993) concluded that the sulfate attack is generally attributed to the reaction of

sulfate ions with calcium hydroxide and calcium aluminate hydrate to form gypsum and


29

ettringite. The gypsum and ettringite formed as a result of sulfate attack is significantly

more voluminous (1.2 to 2.2 times) than the initial reactants. The formation of gypsum

and ettringite leads to expansion, cracking, deterioration and disruption of concrete

structures. In addition to the formation of ettringate and gypsum and its subsequent

expansion, the deterioration due to sulfate attack is partially caused by the degradation of

calcium silicate hydrate(C-S-H) gel through leaching of calcium compounds. This

process leads to loss of C-S-H gel stiffness and overall deterioration of the cement paste

matrix. (Mehta, 1983)

Al Amoudi et al. (1995) and Mangat et al. (1995) studied the behavior and concrete using

supplementary cementing material and found that the incorporation of supplementary

cementing materials such as blast furnace slag, fly ash, and silica fume as partial

replacement of ordinary cement has been found a beneficial technique of enhancing the

resistance of concrete to sulfate attack.

Nabil (2006) studied the sulfate resistance of metakaolin concrete in case of moist cured

and autoclaved cured concrete. He used replacement level of 5%,10% and 15%. Water to

binder ratio was 0.5 and 0.6 with initial moist curing period of (3,7 and 28 days), curing

type ( moist and autoclaving) and air content (1.5% and 5%). After initial moist curing

the specimen were placed in 5% sodium sulfate solution for a total period of 18 months.

The degree of sulfate attack was measured by using concrete prisms, compressive

strength of concrete cubes and visual inspection of cracks. The study showed that MK

replacement of cement increased the sulfate resistance of concrete. This resistance

increases with an increase in the replacement level. Autoclaved MK concrete specimens

showed superior sulfate resistance compared to moist cured one. The air entrained

concrete showed higher improvement in the sulfate resistance than the non air entrained

MK concrete.

2.11 CARBONATION

Carbonation is a risk for reinforced concrete because it can minimize the alkalinity of

concrete to such an extent that, when the PH is reduced below certain values iron may

rust and spalling of cover occurs. To minimize the risk of corrosion of the reinforcement,

the concrete must be dense and the cover sufficiently thick. The depth of carbonation

increases with time and depends on partial pressure of carbon dioxide, temperature,


30

humidity, micro-cracks, cement content, water to cement ratio and curing length. The

main concern with carbonation is the possibility of corrosion of the reinforcing steel. As

for Portland concrete, active corrosion requires both moisture and oxygen in addition to

the loss of steel passivity; thus even when the concrete is carbonated, the rate of corrosion

of reinforcing steel in interior concrete is likely to be low (Lea, 1988).

Verbeck (1956) studied the carbonation in Portland cements and found that carbon

dioxide contained in the air is potentially dangerous for concrete durability as it can attack

all of the hydrates in the hardened cement. In the cement-water-carbon dioxide system the

stable phases are calcium carbonate and silica, alumina and ferric oxide hydrates. This

occurs only in case of poor quality or porous concretes.

Kropp (1983) found that carbonation in case of dense or good quality concrete is low in

comparison to that of porous concrete. He also observed that this is concerned with the

total porosity and specific surface of the cement paste. Thomas et al. (1993) studied the

partially carbonated Portland cement and revealed that the carbon dioxide picked up from

air occurs in the paste mainly as crystalline calcium carbonate. However, a significant

part is also present in a non crystalline form and is probably incorporated in the C-S-H

structure.

Dunster (1996) studied the effect of carbonation on corrosion of high alumina cements

and found that the rate of corrosion in concrete carbonated under laboratory conditions

was more sensitive to relative humidity than is usually seen with the Portland concretes.

Constantinou and Scrivener (1995) studied the corrosion in reinforced concrete due to

carbonation by observing the microstructure have concluded that there is no difference in

the corrosion rate between 70% and 95% relative humidity.

Yoda (2002) carried out a very lengthy research on carbonation of concrete specimens

that were prepared separately using types A, B and C of Portland blast-furnace slag

cement, and Normal Portland cement, and which have the same degree of compressive

strength, on the 28th day of age and also for studying carbonation-preventive effects of

different finishing materials, such as paint, mortar and tiles. The concrete specimens

which were prepared by mixing concrete materials on march 27 and April 6, 1961, and

subsequently compacting with considerable care, were subjected to thorough initial


31

curing, and then were exposed to the indoor and outdoor atmosphere under quite common

weathering conditions for 40 years. As a result of the study, it was concluded that the

carbonated thickness of the concrete after such long-time aging does not differ with types

of cement if the concrete is prepared to have the same degree of compressive strength on

the 28th day of age, and is subjected to careful compaction and initial curing at the time

of placing. In addition, the factor in the carbonation-rate equation that has already

proposed by the author was corrected by taking the carbonated thickness measured this

time into consideration.

According to Batis (2005) the corrosion resistance of concrete influences its durability

and finally its performance. The concrete performance depends mainly on the

environmental conditions, the microstructure and the chemistry of the concrete. He

studied the effect of metakaolin on the corrosion behavior of cement mortars. In his study

he found that the metakaolin improves the compressive strength and the corrosion

behavior of mortar specimens. However, at higher percentages of metakaolin corrosion

resistance is decreased.

2.12 FREEZE –THAW RESISTANCE

Freeze and thaw damage to concrete surfaces is associated with the freezing of concrete

which is critically saturated with water. Fatigue resulting from repeated cycles of freezing

and thawing is more liable to cause damage than the occasional freezing. It caused

cracking parallel to the exposed surface, surface pops out, durability cracking or (D-

cracking), surface spalling and surface scaling . The aggregates can affect freeze- thaw

durability either directly, by being themselves frost susceptible or indirectly by

influencing the properties of the hardened concrete. (Lea,1988)

Aggregate particles are thought to be directly associated with the occurrences of pop-outs,

D-cracking and sometimes surface spalling. West and Shakoor (1984) have describe

argillaceous carbonate aggregates from Indiana, USA which have caused pitting and pop-

outs of concrete pavement surfaces in service. According to Stark (1976), nearly all the

rock types know to be associated with D-cracking (finely closed space surface cracks

which occur parallel and adjacent to joints, larger cracks and free edges) are of

sedimentary origin including lime stones, cherts and shales.


32

Freeze and thaw resistance have been studied by many researchers and it is agreed that it

concerns with the free moisture present inside the concrete either at the time of placement

or due to some external action. However, the present of free moisture is linked with the

pore structure of concrete. Addition of pozzolanic material improves the packing of

concrete matrix and therefore the freeze and thaw resistance of the concrete.

Zhang and Malhotra (1995) during their studies on thermally activated alumina silicate

pozzolanic material (Metakaolin ), regarding their applications on different properties of

concrete found that Metakaolin is very effective in improving the freeze and thaw

resistance of concrete.

Cai and Liu (1998), studied the Freeze-thaw durability of in hydraulic structures located

in cold areas. In his research he evaluated the damage in concrete caused by freezing by

freezing the pore solution in concrete and studied the change of concrete electrical

conductivity with freezing temperatures. Concrete was subjected to the varying freeze and

thaw cycles having temperature ranges of 0 to -20ºC. In freezing process, the concrete

conductivity decreases at -10ºC indicating that pore solution in concrete freezes above

-10ºC than below -10ºC. Finally he concluded that for ordinary concrete frost damages

below -10ºC are negligible.

Qin (2003) investigated the strength and deformation characteristics of plain concrete

under multi-axial compression after different cycles of freeze-thaw. He concluded that the

strength decreases and deformation increases as increasing the number of freeze-thaw

cycles were drawn.

2.13 SUMMARY

This chapter has reviewed the pozzolan used in the concrete technology, types and origin

of pozzolan and how they react with the Portland cement to improve the properties of

concrete. Improvement of key properties of concrete like strength, permeability,

resistance to acid attacks, carbonation, shrinkage , alkali silica reaction and freeze thaw

resistance using pozzolans has been discussed in detail by from the various researchers.

Pozzolans increase the resistance of concrete against environmental attack since they

reduce permeability, absorption and ion diffusity. The resistance of concrete against acids

is definitely increased by the substitution of pozzolan in Portland cement. Sulphate


33

resistance of concrete is also increased when metakaolin is used as a pozzolan.

Carbonation due to atmosphere is also concerned with the micro-structure of concrete. As

the micro-structure of concrete is improved with pozzolans, so it improves the

carbonation resistance of metakaolin concrete. Literature review clearly indicates the

importance of metakaolin to improve the durability of concrete.

CHAPTER-3

34

DEVELOPMENT OF METAKAOLIN 3.1 INTRODUCTION

This chapter discloses main sources of kaolin available in Pakistan. The physical and

chemical properties of the material occurring in nature are also discussed. The first phase

of the research involves the production of metakaolin which highly depends on the

burning temperature and duration to which the kaolin is exposed. It has been observed

that duration of heating and temperature control the pozzolanic activity of the metakaolin.

The experimental program is discussed in detail which leads to the final selection of

optimum temperature and duration for production of reactive metakaolin that will be

incorporated in concrete for durability experimentation which is the main aim of the

study.

3.2 SOURCES OF KAOLIN

Pakistan is an under developed country which possesses abundant natural resources.

Kaolin Clay or more commonly called China Clay is very popular in pottery industry of

Pakistan. This clay is also used worldwide in the production of special type of cements,

paper manufacturing, paint and insecticides industry (Sayamipuk, 2000). There are two

huge deposits of kaolin clay available in Pakistan which are at Shahderai in district Swat

of North West Frontier Province and Nagar Parker in Sindh Province. The total reserves

in Swat are estimated to be 2.8 million tons. Recently some reserves have also been found

in Shahdin and Doshagram near Matta in district Swat. According to a report by Pakistan

Science Foundation (www.psf.gov.pk), the detailed investigation of China Clay deposits

at Nagar Parker area revealed that clay consisted of mainly Kaolinite and Quartz along

with minor traces of Goethite. The China clay is generally covered by a thin layer of

hydrated iron oxides. The clay zone is of varying thickness either in pockets or of

lenticular in nature. The total reserves estimated in this area are 3.5 million tons.

3.3 PROPERTIES OF RAW KAOLIN

Kaolin from Nagar parker was selected for the production of metakaolin primarily due to

its availability in the local market of pottery industry. Kaolin clay obtained was dry and in

the form of lumps. The color of the raw kaolin was whitish, texture was soft and surface

CHAPTER-3 DEVELOPMENT OF METAKAOLIN

35

was smooth (Figure 3.1). During physical feeling of the raw kaolin it appeared to be a

soft material.

Figure 3.1 Kaolin clay obtained from Nagar Parker in the form of lumps.

The chemical composition of raw Kaolin was obtained using flame photometery and

gravimetric analysis, and is reported in Table 3.1.

Table 3.1 Chemical composition of raw kaolin used in the study

Compound SiO2 Al2O3 Fe2O3 MgO CaO Na2O K2O

Moisture Content

(%)

SO3

Kaolin (%) 57.51 25 0.49 0.52 2.18 0.058 0.01 <1 -

ASTM C 618 Limits(%) 70 - - - - 3 4

Courtesy of Pakistan Council of Scientific and Industrial Research (PCSIR) for performing chemical analysis of the samples provided by the author.


36

It may be depicted from table 3.1 that the average silica content is 57%. The chemical

composition of the raw kaolin was compared with ASTM C 618 for its suitability to use it

as a pozzolan. The contents of silica, ferric oxide and aluminum oxide satisfies the

ASTM standards for class “N” pozzolans which is a high quality pozzolan category.

Moisture content of the raw kaolin was below 1% which is well within the ASTM limits.

Sulfur trioxide is also absent in the clay which is a positive characteristic. The ASTM

limits to qualify the pozzolans in concrete is not limited to table 3.1. There are other

parameters that determine the behavior of any pozzolan. These important physical

parameters include fineness, strength activity index, water requirement, soundness and

uniformity requirements.

The fineness of the pozzolan was determined from the wet sieve analysis which was

estimated to be 29%. The wet material was passed through sieve No. 325 and percentage

retained on the sieve was recorded. Class “N” pozzolan qualifies this test if the

percentage retained is less than 34%.

Strength activity index is defined as the ratio of compressive strength of mortars

incorporating pozzolans to the compressive strength of control mortars at age of 7-day

and 28- day. ASTM C 618 gives maximum weight-age to this index. Whereas pozzolan

exhibits strength activity index more than 0.75, it qualifies the important requirements of

pozzolan for incorporating in concrete. This physical test is very important and requires

careful laboratory experimentation before reaching final conclusions. The test has been

discussed in detail in section 3.6.

Water requirement limitations imposed by ASTM C 618 limits are 115% maximum. The

water requirement of the mortar was determined on the basis of flow according to ASTM

109C. The flow shall be within 110 + 5% in twenty five drops of flow table. The mortar

containing metakaolin showed the similar flow to that of control mixture at 106.4%.

The uniformity requirement of pozzolan is applicable when clay is obtained from multiple

sources. This research program utilizes the clay from a single source. However the

density was determined for different samples which were found to be the same.


37

3.4 PRODUCTION OF METAKAOLIN

The detailed literature review has revealed that heating temperatures for conversion of

clays into pozzolan varied from 600ºC to 1000ºC with heating durations of 6 to10 hours

depending mainly on the mineral composition of the clays. On the basis of information

available from literature review it was decided to perform thirteen trials with five heating

temperatures 600°C,700°C, 800°C, 900°C and 1000°C and three durations 6, 8 and 10

hours. The combination details are given in Table 3.2.

Table 3.2 Schedule of calcination of kaolin clay.

S. No.

Heating

temperature

(ºC)

Heating Durations (Hours)

1. 600 6 8 -*

2. 700 6 8 10

3. 800 6 8 10

4. 900 6 8 10

5. 1000 6 8 -*

*Due to cindering of kaolin clay corresponding durations were not used.

3.4.1 Calcination of Kaolin

The calcination process was carried out inside an electronically control computerized

furnace. This furnace had total capacity of 15 Liters and maximum temperature attained

with this furnace was 1100ºC. The furnace gave complete freedom to control the heating

duration with multiple options. Hence there was no concern of over-cooking of material

placed inside the furnace. Due to the capacity limitation, the larger quantities were

calcined in parts. Kaolin clay which was available in the form of dry lumps was stacked


38

inside the furnace with the maximum charge of 10 kilogram. Each charge was calcined as

specified in Table 3.2 and stored separately inside labeled plastic bags.

3.4.2 Processing of metakaolin

The calcination of kaolin clay at varying temperature and duration converted it into

metakaolin. The required metakaolin out of the prepared metakaolin samples (thirteen in

number) needed to be investigated. Figure 3.2 shows kaolin as compared to Metakaolin.

After calcination the metakaolin became much harder and gave ringing noise when

thrown on the concrete floor. The color of the metakaolin also changed to reddish white

due to calcination effect. These lumps of metakaolin were broken into small pieces which

could pass through a sieve having opening size of 0.5 inches. The pieces were then passed

though a grinding machine for conversion into fine powder.

Figure 3.2 Kaolin (Left) and Metakaolin (Right)

The grinding machine used to grind the metakaolin was locally prepared. This machine

has three major portions: material charging portion, processing portion and discharge

portion.

Material charging portion was located at the top of the grinding machine. The processing

portion contains a circular steel disc with steel blades. This disc rotates with the help of

powerful electric motor and performs the grinding of the material. A very fine steel mesh

is located around the periphery of the circular disc. The grinded material is forced to pass

through the mesh. The particle size or fineness of the material can be very easily

KaolinMetakaolin


39

controlled by using sieves with very fine openings. The grinded material discharges out

from the lower portion of the machine which is also called as discharge portion. The

physical properties of fine powdered metakaolin are reported in Table 3.3.

Table 3.3 Physical properties of metakaolin

Specific gravity Blaine’s fineness (m2/kg) Color

2.64 645 White with a slight tinge of red color

3.5 CHARACTERIZATION BY X-RAY DIFFRACTION ANALYSIS

The main task was to determine the calcination temperature and duration at which the

metakaolin must be prepared for incorporation in concrete. The Metakaolin calcined at

different temperatures and durations was subjected to X-ray diffraction analysis. X-ray

diffraction gives the quick analysis of the material which may be confirmed later by

pozzolanic activity tests. Table 3.4 gives detail of the location of corresponding oxides

present inside the metakaolin with reference to their angle of refraction (2θ).

Table 3.4 2θ Values for different Peaks for XRD analysis.

S.No. 2θ (Degrees) Compound (%)

1 57.56 Al2O3

2 37.604 CaO

3 33.25 Fe2O3

4 39.49 K2O

5 43.03 MgO

6 46 Na2O

7 26.587 SiO2

In this analysis the major/important oxides present in the metakaolin were observed. This

analysis gave the peak of different constituent materials present in the pozzolan calcined


40

at different temperatures. The silica peaks are linked with the pozzolanic activity of the

metakaolin. Stronger peaks indicate higher activity of the constituent material. XRD

analysis is given in Figures 3.3 to 3.9. The calcination temperature and duration is marked

on each figure. The silica content shows the maximum activity at two theta value of

26.587°.

Figure 3.3 XRD analysis for thermally activated kaolin at 600°C for 6 hour duration. The careful observation of silica peak counts in case of figure 3.3 and 3.4 shows that the

peak counts are less than four hundred for calcination temperature of 600°C. However in

figure 3.4 the silica peak counts slightly jump higher but still remain less than four

hundred. Another important feature was observed in the two figures 3.3 and 3.4 that all

the peaks were sharp which indicates that the process of crystallization has not yet started.

The peaks of the remaining oxides can also be observed which are still in the

development phase. The peaks of the remaining oxides become prominent for the other

XRD images.

K2O 600˚C – 6 hrs

Si O2

CaO

Fe2O3 Na2O Al2O3

MgO

S#1


41

Figure 3.4 XRD analysis for thermally activated kaolin at 600°C for 6 hour duration.

Figure 3.5 XRD analysis for thermally activated kaolin at 700°C for 6, 8 and 10 hour duration.

600˚C – 8 hrsK2O

SiO2

MgOCaO

Fe2O3 Na2O Al2O3

700˚C – 6 hrs

700˚C – 8 hrs

700˚C – 10 hrs

K2O

SiO2 MgO

CaO Fe2O3 Na2O Al2O3

K2O

SiO2 MgO


K2O

SiO2 MgO


S#2


42

Figure 3.5 gives the XRD image for calcination temperature of 700°C. It clearly indicates

the increase in the silica peak counts which are slightly higher than 1000. The trend is

same for the all the three calcination duration i.e. 6, 8 and 10 duration. There are also no

signs of crystallization at this calcination temperature because all the peaks are sharp in

nature. Some other peaks were also observed at this temperature.

The XRD analysis for metakaolin calcined at 800°C for 6, 8 and 10 hour duration was

given in figure 3.6. The peaks are more or less similar to that of figure 3.5. However, in

this case peak counts are much higher than 1000. There are also no signs of

crystallization at this calcining temperature.

Figure 3.6 XRD analysis for thermally activated kaolin at 800°C for 6, 8 and 10 hour duration.

Rounded peak and lesser silica peak counts were observed in XRD image obtained at

900°C calcination temperature. The silica peak counts lower than 1000 clearly indicates

the decrease in pozzolanic activity. Rounded peaks present in the image also corroborate

the initiation of crystallization process. Up to this stage the variation in the peak counts

from lower to higher was observed for Figure 3.3 to 3.6 and then from higher to lower for

K2O

SiO2 MgO


K2O

SiO2 MgO


K2O

SiO2 MgO


800˚C – 6 hrs

800˚C – 8 hrs

800˚C – 10 hrs


43

Figure 3.6 to 3.7. This trend shows that the peak counts should drop for kaolin clay when

calcined above 900°C.

Figure 3.7 XRD analysis for thermally activated kaolin at 900°C for 6, 8 and 10 hour duration. The peak counts were lower in case of calcination temperature 1000°C as may be

depicted from figure 3.8 and 3.9. It shows that the pozzolanic activity fell from higher to

lower with increasing calcination temperatures. The crystallization process is further

strengthened at this stage. This also indicates that further heating of the clay will not

improve the pozzolanic activity. It also strongly supports the fact that at lower calcining

temperatures the calcining duration does not play any important role. However, at the

desired calcining temperature, which bring the chemical changes in the clay, the

pozzolanic activity increases or decreases with even the slight variation in the heating

duration. Hence the main contributing factor for improving the pozzolanic activity was

the calcining temperature but calcining duration does the fine tuning of the process in

order to get the maximum pozzolanic activity.

900˚C – 6 hrs

900˚C – 8 hrs

900˚C – 10 hrs

K2O

SiO2 MgO


K2O

SiO2 MgO


K2O

SiO2 MgO



44



S#13

1000˚C – 6 hrsK2O

SiO2

MgOCaO

Fe2O3 Na2O Al2O3

1000˚C – 8 hrsK2O

SiO2

MgOCaO

Fe2O3 Na2O Al2O3

S#12


45

It may be concluded from the foregoing discussion that the maximum pozzolanic activity

is enhanced when the kaolin clay is calcined at 800°C. However, the peak counts were

higher for both 6 and 8 hour calcining durations. The metakaolin samples were further

characterized by the ASTM C 311 which confirmed the maximum pozzolanic activity of

metakaolin when calcined for eight hours. Section 3.6 discusses in detail the

characterization of metakaolin by using ASTM C 311 which is standard test method for

sampling and testing of natural pozzolan for their use in concrete.

3.6 CHARACTERIZATION BY MECHANICAL STRENGTH

ASTM C 311 outlines the complete procedure for the determination of strength activity

index for any material to be used as a pozzolan with cement. This is an essential

requirement for any material to qualify as a pozzolan test according to ASTM C 618. This

physical test requirement is very powerful in a sense that it supersedes all other tests if

qualified. Strength activity index is given by the following expression.

SAI % x 100

Where

= compressive strength of standard mortar of cement, sand and pozzolan at given age

= compressive strength of control mortar at the same age as that of .

ASTM C 109 C/ 109 M gives the complete detail for the preparation of standard mortar

of cement, sand and pozzolan. According to this standard twenty percent of cement

should be replaced with the pozzolan by weight. The weight of the sand should be 2.75

times of binder and water to binder ratio for the standard mortar or control mortar should

be maintained at 0.49.

3.6.1 Experimental Details

Fifteen mortar mixtures were prepared and used in the study according to ASTM C 109/C

109M for determination of strength activity index (SAI). Metakaolin (as explained in

section 3.4) obtained by calcination at different temperatures and durations was used in

these mixtures. The mixture containing only cement and sand was denoted by “A” and is

also known as control mixture. In mixture “B” fine sand passing sieve no. 52 and retained


46

on sieve no. 100 was used in order to investigate the filler effect of the metakaolin. The

mixtures “C” to “O” contain metakaolin prepared at different temperatures and durations.

The metakaolin was replaced twenty percent of cement by weight. The detail of each

mixture is given in Table 3.5.

Table 3.5 Mix proportions of mortars

Mix

ID

CT

(°C)

HD

(Hours)

Cement

(gms)

MK

(gms) W/b

Sand

(gms)

Fine Sand (gms)

A - - 1350 0 0.49 3713 -

B - - 1080 0 0.49 3713 270*

C 600 6 1080 270 0.49 3713 -

D 600 8 1080 270 0.49 3713 -

E 700 6 1080 270 0.49 3713 -

F 700 8 1080 270 0.49 3713 -

G 700 10 1080 270 0.49 3713 -

H 800 6 1080 270 0.49 3713 -

I 800 8 1080 270 0.49 3713 -

J 800 10 1080 270 0.49 3713 -

K 900 6 1080 270 0.49 3713 -

L 900 8 1080 270 0.49 3713 -

M 900 10 1080 270 0.49 3713 -

N 1000 6 1080 270 0.49 3713 -

O 1000 8 1080 270 0.49 3713 - *To study filler effect of metakaolin for sand passing #52 and retained#100 CT = Calcination Temperature: HD = Heating Duration: MK = Metakaolin


47

The normal consistency of cement with 20% replacement of metakaolin was determined

at first which was found to be 0.38. However, in case of neat cement paste the normal

consistency was obtained at 0.3. The mortars were mixed on a non porous platform. Six

mortar cubes of 70 mm in size were cast for each mixture. The mixing of cement and

metakaolin was carried out for three minutes or until the color of the binder became

uniform. After thorough mixing, water was added to the dry mixture and the whole

material was mixed again until the paste became uniform. Seventy mm cubes were filled

with the paste and covered with plastic sheet to avoid the loss of moisture. The same

procedure was repeated for the other mixtures given in Table 3.5. After twenty-four hours

cubes were de-molded, marked and transferred to the curing tank. Three cubes were taken

out of the curing tank at each testing age.

3.6.2 Strength Activity Index

3.6.2.1 Seven Day Index Figure 3.10 depicts the comparison of compressive strength of different mortar cubes at

seven days. Replacement of cement by sand was done in one of the mix to confirm the

effect of chemical reactivity of the metakaolin. Metakaolin with low peak counts (600°C)

when used with cement as a pozzolan clearly indicates the lower compressive strength of

the mortars. This was due to the fact that silica content was less to complete the chemical

reaction between cement and pozzolan in order to build the strength of the cement paste.

Figure 3.10 shows that when the metakaolin with more silica count was used as a

pozzolan with cement, it resulted in higher compressive strength. This fact is based on the

completion of hydration reaction taking place between cement, pozzolan and fine

aggregate. However, the replacement level which was maintained at twenty percent was

not to be considered as the final replacement level as the change in replacement level may

influence the compressive strength.

The compressive strength is higher for mixture in which clay calcined at 800˚C for 8

hours is incorporated as shown in figure 3.10. This higher compressive strength was

observed for the same metakaolin, which showed, higher peak counts in case of X-ray

diffraction analysis. The results shown in figure 3.10 also testify the XRD results given in

section 3.5.


48

As discussed in section 3.5 the variation in the duration of heating in case of specific

temperature only accounts for the fine tuning of kaolin. Due to this fact compressive

strength was dropped for almost all mixtures in which kaolin clay was burnt at 10 hours.

However, major reduction in compressive strength was observed for the mixtures having

metakaolin calcined above 800°C. This major reduction in compressive strength of the

mortar mixtures was due to the change of the nature of metakaolin used in the mixtures.

The structure of metakaolin starts changing from amorphous to crystalline when the

calcining temperature rises above 800°C and results in the loss of reactivity of metakaolin

which is clearly indicated in figure 3.10.

Figure 3.10 Compressive strength of mortar mixes at seventh day 3.6.2.2 Twenty Eight Day Index

Twenty eight days compressive strength of mortar cubes is shown in figure 3.11. This

graphical information has been obtained from the compressive test results of mortar

mixtures given in Table 3.5. These results show peaks similar to that of seven day results

with increased compressive strength values. It also indicates that maximum pozzolanic

15

20

25

30

35

600°C 700°C 800°C 900°C 1000°C Control Fine Sand

Com

pres

sive

str

engt

h(N

/sq.

mm

)

6 hrs8 hrs10 hrs


49

reactivity is exhibited by the clay calcined for 8 hour duration at 800˚C. The strengths of

various cubes are at par with the control specimen where as the specimen in which fine

sand instead of kaolin was used showed a great decrease in strength which is a clear

indicator of effective chemical reactivity of kaolin.

Figure 3.11 Compressive strength of mortar mixes at 28 days

The graphical presentation of strength activity index for mixtures given in table 3.5 is

shown in figure 3.12 for both seven and twenty eight day’s compressive test results.

Comparison of above values with ASTM C 618 limits for the physical tests clearly

indicates that nearly for all the mixtures having pozzolan, strength activity index value is

more than 75 percent. Strength activity index (SAI) value is higher in case of mix “I” than

that of all other mixes in figure 3.12. This physical test also validates the finding of X-

Ray Diffraction analysis discussed in section 3.5.

15

20

25

30

35

40

600°C 700°C 800°C 900°C 1000°C Control Fine Sand

Com

pres

sive

str

engt

h(N

/sq.

mm

)

6 hrs8 hrs10 hrs


50

Figure 3.12 Strength activity Index (%) for Mortar mixes at 7 and 28 days 3.7 DISCUSSION ON STRENGTH ACTIVITY INDEX RESULTS

The results discussed in case of section 3.5 and section 3.6 are two independent methods

for verifying the pozzolanic behavior of metakaolin. However, both of the discussions

reach to the same conclusion. In the light of discussion made above, it is concluded that

Kaolin clay obtained from Nagar Parker can be converted to highly reactive metakaolin

when calcined at 800˚C for 8 hour duration. Increase in calcining temperature beyond

800°C results in crystallization of kaolin clay and the loss of reactivity of metakaolin.

However, for calcining temperatures lower than 800°C, results, in lack of proper

activation of silica content or lower peak counts of silica in case of X-ray diffraction

analysis.

Hence the use of processed kaolin clay (Metakaolin) obtained from Nagar Parker is

recommended as a supplementary cementing material.

60.00

70.00

80.00

90.00

100.00

110.00

C D E F G H I J K L M N O

Mortar Mixtures

Stre

nght

Act

ivity

Inde

x (%

)

SAI (%)(7-DAYS)SAI (%)(28-DAYS)


51

3.8 SUMMARY

Kaolin clay obtained from Nagar Parker was calcined at different temperatures ranging

from 600 to 1000ºC for 6 to 10 hours duration. After calcination the clay was broken to

fragments and crushed to fine powder to the Blaine’s value of 645 m2/Kg. X-ray

diffraction analysis was carried out for the determination of reactivity of silica content.

Strength activity index was also determined using ASTM C 311 in order to justify the

physical requirement of ASTM C 618 for pozzolans. The calcining temperature of 800°C

for 8 hour duration was recommended for preparation of metakaolin clay. The X-ray

diffraction results also corroborated the strength activity Index test.

CHAPTER-4

52

EXPERIMENTAL PROGRAM 4.1 INTRODUCTION

Acids cause deterioration of concrete due to their ability to dissolve the soluble compounds

present in concrete. These compounds when dissolved result, in the exposure of

reinforcement due to spalling of concrete and further effects due to rusting of reinforcement

thus endangering the whole structure. Sulfuric acid is the only one among strong acids

which may occur naturally in ground waters and soils. The oxidation of certain sulfide

minerals specially the iron disulfides, pyrite and marcasite, FeS2, results in the production

of sulfuric acid in presence of air and moisture (Lea, 1988).

It has been observed from literature review in Chapter two that various researchers

performed experiments according to their specialized needs and circumstances. The

determination of rate of attack on control and metakaolin concrete due to sulfuric acid of

varying concentrations was not possible to determine from the data published by other

researchers. Therefore the experimental program had to be designed in such a way that

effect of acids both on control and metakaolin concretes may be determined. This study is

mainly focused on the loss of strength in metakaolin concrete when exposed to acidic

environment for strong and weak acids in comparison to the control concrete. The rate of

acid attack in relation to the replacement level of the metakaolin has been studied in detail.

The study also included the performance of metakaolin concrete with variable water to

binder ratios. Tests to determine carbonation depths both for control and metakaolin

concrete have been carried out for the maximum exposure of one year.

The experimental program has been designed in such a way as the strength loss of

metakaolin and control concretes may be studied with respect to the binder content,

metakaolin-binder ratio, water-binder ratio, time of acid exposure and the strength of acid

solution. After careful analysis of results, the strength of concrete has been modeled where

the main parameters like binder content, water-binder ratio, metakaolin-binder ratio, acid

strength, acid type and age of acid exposure have been taken into account. Similarly

carbonation depth has been determined by varying binder content and metakaolin quantity

in order to formulate the statistical model governing the carbonation depth of concrete. A

CHAPTER-4 EXPERIMENTAL PROGRAM

53

brief account of the experimental program is presented by using flow charts and the details

are also given in tabular form. The results of the test program have been discussed at the

end of this chapter.

4.2 TEST PROGRAM

The response of metakaolin to the acid attack and carbonation was determined and

compared with that of control concrete. The test program included four basic materials,

cement, sand, gravel and metakaolin. In the test program three water-binder ratios (0.45,

0.55 and 0.65) were used. Two binder contents of 300 kg/m3 (Group-1) and 400 kg/m3

(Group-2) were employed along with the four replacement levels (0%, 15%, 20% and 25%)

of metakaolin by weight of binder content. The mixtures without metakaolin were termed

as “control mixtures”. The specimens were exposed to two different acids after twenty

eight days curing at room temperature. The acids used in the study were sulfuric and acetic

acid. Sulfuric acid was used for determination of response of metakaolin against strong acid

while Acetic acid was used for determination of response of metakaolin concrete against

weak acids. The specimens were exposed to three solution strengths of two acids i.e. 2%,

5% and 8% for maximum of six month duration. The compressive strength of the concrete

cubes exposed to acid attack was determined at an interval of 7, 28, 91 and 182 days in

order to determine the rate of degradation of concrete subjected to acid attack. The

degradation was determined with reference to twenty eighth day strength of concrete. The

results were plotted graphically to determine the behaviour of metakaolin concrete due to

change in water-binder and metakaolin-binder ratio.

The rate of carbonation depth was determined for both the binder contents. The specimens

involved in carbonation depth determination were similar to those used in acid attack

determination i.e. having three water to binder ratios (0.45, 0.55 and 0.65) and four

metakaolin to binder ratios (0, 0.15, 0.20 and 0.25) . These specimens were placed in open

atmosphere after twenty eight days of curing. Carbonation depth was determined after of 4,

7, 13, 25 and 52 weeks of exposure. Phenolphthalein indicator was used for the

determination of carbonation depth. As the carbonation effect penetrates from the outer

surface of the specimen toward the inner core of specimen, therefore the specimens were

cut into two pieces before subjecting to phenolphthalein.


54

4.2.1 Designation for Control and Metakaolin Concrete. There are four parameters which are used to describe the designation of mixtures, binder

content, metakaolin-binder ratio, water-binder ratio and acid strength to which the concrete

is exposed. Keeping in view all the four parameters the designation for concrete is given in

Table 4.1 and 4.2.

Table 4.1(a) Mixture proportions of control and metakaolin concrete by weight for binder content 300 kg/m3

Mixture ID Cement

(kg/m3)

Metakaolin

(kg/m3) Water

(kg/m3)

Fine

Aggregate

(kg/m3)

Coarse

Aggregate

(kg/m3)

Remarks

300M00W45 300 0 135 660 1320 Control-1

300M15W45 255 45 135 660 1320

300M20W45 240 60 135 660 1320

300M25W45 225 75 135 660 1320

300M00W55 300 0 165 630 1260 Control-2

300M15W55 255 45 165 630 1260

300M20W55 240 60 165 630 1260

300M25W55 225 75 165 630 1260

300M00W65 300 0 195 600 1210 Control-3

300M15W65 255 45 195 600 1210

300M20W65 240 60 195 600 1210

300M25W65 225 75 195 600 1210

The above designation may be expressed in general form as given by the following

equation.

bbbMmmWww 4.1

Where “bbb” denotes the binder content, “mm” in “Mmm” stands for metakaolin-binder

ratio expressed in percentage, “ww” in “Www” indicates the percentage of water-binder

ratio.


55

For example in Table 4.1 (a), mixture ID “300M20W65” denotes that sample belonged to

binder content 300 Kg/m3 having metakaolin-binder ratio of 20% and water-binder ratio of

65%.

The mixture details given in table 4.1(b) follow same designation and have been prepared

for binder content 400 kg/m3 .

Table 4.1(b) Mixture composition of control and metakaolin concrete by weight for binder content 400 kg/m3

Mixture ID Cement

(kg/m3)

Metakaolin

(kg/m3) Water

(kg/m3)

Fine

Aggregate

(kg/m3)

Coarse

Aggregate

(kg/m3)

Remarks

400M00W45 400 0 180 592 1184 Control-1

400M15W45 340 60 180 592 1184

400M20W45 320 80 180 592 1184

400M25W45 300 100 180 592 1184

400M00W55 400 0 220 560 1112 Control-2

400M15W55 340 60 220 560 1112

400M20W55 320 80 220 560 1112

400M25W55 300 100 220 560 1112

400M00W65 400 0 260 520 1040 Control-3

400M15W65 340 60 260 520 1040

400M20W65 320 80 260 520 1040

400M25W65 300 100 260 520 1040

The study was based on twenty four mixtures for the durability determination of concrete

using metakaolin against acid resistance and carbonation. Twelve mixtures were

proportioned for 300 kg/m3 binder content and remaining twelve for 400 kg/m3 binder

content. The designation of the mixtures clearly indicates the binder content, metakaolin-

binder ratio and water-binder ratio of the mixture. The mixtures marked as control-1, 2 & 3

(Table 4.1a) contain no metakaolin. Remaining nine mixtures (Table 4.1a) other than

control have different metakaolin-binder and water-binder ratios. For each mixture


56

recorded in Table 4.1a contains one hundred and twenty cubes (100 mm size) for acid

attack and carbonation depth determination. The complete detail is given in Table 4.2(a)

and 4.2(b).

Table 4.2(a) Test age and sample detail for a single mixture exposed to acids

Crushing strength age before

immersion into acids

Crushing strength age after immersion into acids Total

Age (days) 7 28 7 28 91 182 Compressive

Strength 03+1* 03+1* - - - - 08

Sulfuric Acid

2% - - 03+1* 03+1* 03+1* 03+1* 16

5% - - 03+1* 03+1* 03+1* 03+1* 16

8% - - 03+1* 03+1* 03+1* 03+1* 16

Acetic Acid

2% - - 03+1* 03+1* 03+1* 03+1* 16

5% - - 03+1* 03+1* 03+1* 03+1* 16

8% - - 03+1* 03+1* 03+1* 03+1* 16

Sub Total 104

*one extra sample was reserved for each age

Table 4.2(a) Test age and sample detail for a single mixture exposed to acids

Carbonation depth age after twenty eight days of curing Total

Age (weeks) 4 7 13 25 52 No. of Samples 03 03 03 03 03 15

Sub Total 15

Grand Total 119

One hundred and five cubes were used to determine the response of control and metakaolin

concrete for varying acid exposure and durations as shown in Table 4.2(a). The response of

metakaolin concrete was determined in comparison to the control concrete by observing the


57

influence of metakaolin-binder and water-binder ratio. The designation regarding further

characterization of the samples within a mixture is mentioned in Table 4.3 which gives

complete information about binder content, type of acid and solution strength of each acid

to which samples were exposed.

Fifteen cubes (100 mm size) were reserved for carbonation depth measurement for each

mixture as shown in Table 4.2(b). These cubes were placed in open atmosphere for

determination of carbonation depth. The process of carbonation is relatively a slow process;

therefore the ultimate duration of this test considered was fifty two weeks. Carbonation

depth was determined at different durations; therefore, its designation was further modified

in order to take into account the testing age for each mixture. The designation for

carbonation samples for each mixture of Table 4.1 is given in Table 4.4. The designation

used for carbonation samples within each mixture included the binder content, metakaolin-

binder ratio, water-binder ratio and testing age in week.

Tables 4.1(b) depict the designation of mixtures with binder content of 400 kg/m3. The

designation used in Table 4.1(b) was similar to that used in Table 4.1(a). There were again

twelve mixtures for 400 kg/m3 binder content out of which three mixtures were reserved as

control mixtures already mention in Table 4.1b. One hundred and twenty cubes (100mm

size) were prepared from each mixture out of which one hundred and five were exposed to

acid attack and fifteen were placed for outdoor exposure to measure the carbonation depth.

Each mixture was further characterized according to the type of acid and the solution

strength in order to facilitate the reporting of the results. The designation adopted for acid

samples within a mixture is given in Table 4.3 while for carbonation samples are reported

in Table 4.4.

The test program is also outlined in Figure 4.1 & 4.2 for binder contents 300 and 400 kg/m3

which give the complete information regarding the preparation of mixtures.


58

Figure 4.1 The outline of the control and metakaolin mixtures for durability determination against acids (Group-1)

Control Concrete (Group-1)

Cement content = 300 kg/m3

Sand = 660 kg/m3 Aggregates = 1320 kg/m3 Water = 135 kg/m3



3 Control

Mixtures

Metakaolin Concrete (Group-1)

Binder content Cement + Metakaolin = 300 Kg/m3

Metakaolin = 45 kg/m3

Sand = 660 kg/m3 Aggregates = 1320 kg/m3





Total metakaolin mixtures =9

100 mm cubes Tested at Ages

7 & 28 days (Before immersion)

7,28,91,182 days (Compressive strength was

determined after immersion in acids)

Water-Binder ratios 0.45, 0.55 & 0.65


59

Figure 4.2 The outline of the control and metakaolin mixtures for durability determination against acids (Group-2)

Control Concrete (Group-2)

Cement content = 400 kg/m3

Sand = 592 kg/m3 Aggregates =1184 kg/m3 Water =180 kg/m3



3 Control

Mixtures

Metakaolin Concrete (Group-2)

Binder content Cement + Metakaolin = 400 Kg/m3







Total metakaolin mixtures =9

100 mm cubes Tested at Ages

7 & 28 days (Before immersion)

7,28,91,182 days (Compressive strength was

determined after immersion in acids)

Water-Binder ratios 0.45, 0.55 & 0.65


60

4.2.2 Designation of Test Specimens within a mixture The concrete specimens after curing for 28 days were subjected to attack of two acids;

sulfuric acid from strong acid family and acetic acid from a weak acid family. Three

different solution strengths were used for each type of acid as 2%, 5% and 8%. The acid

type and solution strengths were incorporated in the previous designation as given by

equation 4.1 in-order to differentiate the samples within each category. The designation

used has been mentioned in Table 4.3.

Table 4.3 Designation of samples for placement in acids of variable solution strength

Mixture ID Acid Solution strength (%) Sample ID

bbbMmmWww

Sulfuric

2 BbbMmmWwwS2

5 BbbMmmWww S5

8 BbbMmmWww S8

Acetic

2 BbbMmmWww A2

5 BbbMmmWww A5

8 BbbMmmWww A8

Sample designation used in Table 4.3 is the continuation of equation 4.1. The additional

parameter (S/ A) represents Sulfuric acid or Acetic acid respectively and 2, 5 & 8 denotes

the strength of acidic solution. For example mixture ID “400M25W55S5” indicates a

sample prepared with binder content 400 Kg/m3, metakaolin-binder ratio of 25% ,water-

binder ratio of 55% and to be exposed to sulfuric acid solution with 5% concentration.

The samples prepared for mixture proportions given in Table 4.1a and 4.1b were also used

for the carbonation samples as well. The carbonation depth was determined by exposing the

sample to open atmosphere; therefore, the designation used in case of carbonation samples

of each mixture was only based on testing age. The age of testing was recorded in week

instead of days in the carbonation test. The designation of samples used for carbonation


61

depth is given in Table 4.4. The designation used in Table 4.4 is also the continuation of

equation 4.1.

Table 4.4 Designation of samples for Carbonation

Mixture ID Test Age (week) Sample ID

bbbMmmWww

4 BbbMmmWww T04

7 BbbMmmWww T07

13 BbbMmmWww T13

25 BbbMmmWww T25

52 BbbMmmWww T52

The sample identification given in Table 4.4 may be written in general form as follows

bbbMmmWwwTtt 4.2

Where “bbb” denotes the binder content, “mm” in “Mmm” stands for metakaolin-binder

ratio expressed in percentage, “ww” in “Www” indicates the percentage of water-binder

ratio and “tt” in “Ttt” represents the exposure of concrete in weeks.

For example the mixture ID “300M25W45T04” denotes that sample prepared with binder

content 300 Kg/m3 having metakaolin-binder ratio of 25% , water-binder ratio of 45% and

to be exposed to 04 weeks of exposure to atmosphere.

4.3 PHYSICAL AND CHEMICAL PROPERTIES OF MATERIALS

The four basic materials which have been used in the entire test program included a single

Portland cement, metakaolin (as processed in chapter-3) and a single set of fine and coarse

aggregates. The change in physical parameters of these materials changes the entire

behavior of the mixture. For example, if a fine or coarse aggregate becomes wet in a

rainfall then it will change the mixture properties due to variation in the moisture content of

the aggregates. Therefore, extreme care was exercised during the storage of the all the

materials used in study. The physical properties which were determined for the materials


62

were kept constant by ordering all the materials at the same time and covering the entire

materials with the plastic sheets in order to avoid any unavoidable change in proportions.

4.3.1 Cement

The chemical analysis of the cement is given in Table 4.5. ASTM C 150-04 gives

theoretical compounds also called Bogue compounds which were derived from the

chemical analysis of the cement. These compounds results during the hydration of the

cement. These compounds can be measured experimentally but Bogue gave the formulae to

calculate these compounds through chemical analysis. Bogue compounds are not very close

to the actual result. However calculation of compounds through Bogue’s formulae is

universally accepted.

4.3.2 Metakaolin

The metakaolin used in this study was the same whose development was presented

comprehensively in chapter-3. The chemical composition of kaolin is given in Table 4.5.

The physical properties of metakaolin are mentioned in the Table 4.6. The fineness of

metakaolin was almost twice that of cement used in this study. However, metakaolin was

lighter than cement due to its low specific gravity. The chemical composition of cement is

also given in Table 4.5.

4.3.3 Fine and Coarse aggregates

The physical properties of aggregates are given in Table 4.7. Fine aggregate was the

Lawrencepur sand which has coarser grain size than all the sands present in Punjab

province. This sand is used in almost all of the construction projects as it gives good

packing in combination with the Margalla crush which was the coarse aggregate used in

this study.


63

Table 4.5 Chemical composition of Portland cement and kaolin

Oxides/ Bogue Compounds

Weight of Oxide, %

Portland Cement Kaolin

CaO 62.11 2.18

SiO2 19.54 57.51

Al2O3 6.73 25

Fe2O3 2.78 0.49

MgO 2.66 0.52

Na2O 0.18 0.058

K2O 0.33 0.01

SO3 2.62 -

Bogue’s potential compound composition(%) of Portland cement

C2S 20.0

C3S 47.7

C3A 13.2

C4F 8.5

Table 4.6 Physical properties of cement and metakaolin

Property Portland Cement Metakaolin

Color Grey White with a slight tinge of red

Blaine Surface Area (m2/kg) 340 645

Density (kg/m3) 3150 2640

Table 4.7 Properties of Aggregates

Aggregates Sp. Gravity Maximum Size Fineness Modulus

Coarse 2.63 12.5 mm 6.67

Fine 2.65 2.32 mm 2.85


64

4.4 TEST RESULTS FOR BINDER CONTENT 300 kg/m3

The mixtures were cast according to the proportions given in Table 4.1a and also outlined

in Figure 4.1. Compressive strength of the cubes were determined according to ASTM

109/C and recorded in tabular form.

4.4.1 Strength of Metakaolin Concrete

The compressive strength of the mixtures was determined after seven and twenty eight days

of curing. The specimens were taken out of curing tank, wiped and placed in open

atmosphere for drying before determining their compressive strength. The compressive

strength results for control and metakaolin concrete are shown in Table 4.8.

Table 4.8 Average compressive strength for cubes

Mixture ID Mix proportion by weight Compressive

Strength (MPa)

Cement Metakaolin Sand Gravel Water 7 - day 28- day

300M00W45 1 0 2.2 4.4 0.45 30.67 40.8

300M15W45 0.85 0.15 2.2 4.4 0.45 36.35 47.78

300M20W45 0.80 0.20 2.2 4.4 0.45 35.26 46.35

300M25W45 0.75 0.25 2.2 4.4 0.45 30.73 40.07

300M00W55 1 0 2.1 4.2 0.55 27.22 36.2

300M15W55 0.85 0.15 2.1 4.2 0.55 32.81 43.13

300M20W55 0.80 0.20 2.1 4.2 0.55 30.84 40.54

300M25W55 0.75 0.25 2.1 4.2 0.55 28.00 36.81

300M00W65 1 0 2.0 4.0 0.65 23.83 31.70

300M15W65 0.85 0.15 2.0 4.0 0.65 29.37 38.6

300M20W65 0.80 0.20 2.0 4.0 0.65 26.51 34.85

300M25W65 0.75 0.25 2.0 4.0 0.65 25.71 33.8


65

Twenty eight days results are presented in graphical format in Figure 4.3. The results

clearly indicate that maximum pozzolanic activity was observed when the metakaolin-

binder ratio is 15 percent. The increase in the cement- binder ratio decreases the

compressive strength of the mixtures. However in this study, compressive strength is one

parameter and the durability is another. Hence the twenty-eight day strength will be used as

reference for durability studies.

Figure 4.3 Compressive strength at twenty eight days

4.4.2 Resistance to Sulfuric Acid

After twenty-eight days of curing the specimens were transferred to the tanks filled with

sulfuric acid solution of variable strength. The solution strengths used in this study were

2%, 5% and 8%. At the specific age of testing the specimens were taken out of acid

0.00

10.00

20.00

30.00

40.00

50.00

60.00

0.4 0.45 0.5 0.55 0.6 0.65 0.7

W/B ratio

Com

pres

sive

stre

ngth

(MP

a)

300M00300M15300M20300M25


66

solution and allowed to dry. The compressive strengths of cubes were determined at 7, 28,

91 and 182 days immersed in acid solution of variable strength. The average compressive

strengths are given in tabular form in Table 4.9 to 4.11. The results were also plotted

graphically to determine the behavior of control and metakaolin concrete in acids.

Table 4.9 Average compressive strength for cubes immersed in 2% sulfuric acid

Mixture ID Compressive

Strength (28 days)

Compressive strength for immersion period in acids (MPa)

7-days 28-days 91-days 182 days 300M00W45S02 40.8 40.58 39.38 36.30 31.85 300M15W45S02 47.78 47.50 46.41 43.19 38.61 300M20W45S02 46.35 46.21 45.97 45.29 44.40 300M25W45S02 40.07 39.96 39.80 39.31 38.61 300M00W55S02 36.2 35.76 34.81 31.92 28.00 300M15W55S02 43.13 42.74 41.73 38.56 34.22 300M20W55S02 40.54 40.40 40.20 39.56 38.61 300M25W55S02 36.81 36.72 36.36 35.52 34.32 300M00W65S02 31.70 31.47 30.43 27.74 24.01 300M15W65S02 38.6 38.32 37.45 34.81 31.22 300M20W65S02 34.85 34.75 34.46 33.35 31.85 300M25W65S02 33.8 33.70 33.29 32.26 30.85



Strength (28 days)




67



Strength (28 days)



Table 4.9 to 4.11 list the compressive strength results for 2%, 5% and 8% solution strengths

of sulfuric acid. The strength decreases with age for all the mixtures. However an increase

in compressive strength results was observed with increase in metakaolin-binder ratio in

comparison to control mixtures. This aspect is clarified from the graphical information of

these results presented below.


68

Figure 4.4 Deterioration of compressive strength at water-binder ratio = 0.45


0.00

10.00

20.00

30.00

40.00

50.00

60.00

0 50 100 150 200

Com

pres

sive

Str

engt

h(M

Pa)

Immersion period(Days)

300M00W45S02300M15W45S02300M20W45S02300M25W45S02

0.00

10.00

20.00

30.00

40.00

50.00

60.00

0 50 100 150 200

Com

pres

sive

Str

engt

h(M

Pa)


300M00W55S02300M15W55S02300M20W55S02300M25W55S02


69


Figures 4.4 to 4.6 depict the response of control and metakaolin concretes immersed in 2%

sulfuric acid solution. The curves clearly show that the metakaolin concrete performed

better at all the ages of exposure in comparison with the control concrete.

The slope of the curves presents the deterioration of strength while immersed in acid

solutions. It can be observed that deterioration rate is almost identical in case of control and

M15 concretes, whereas M20 and M25 concretes performance is at par with each other and

better than control and M15 concretes. It may be safely concluded that in this case

performance of M25 is the best.

Concrete cube when exposed to two percent solution strength of sulfuric acid deteriorated

to a very low extent as shown in Figure 4.7. The deterioration level only affect the surface

of the cube by eating up very thin layer of cement.

0.00

10.00

20.00

30.00

40.00

50.00

60.00

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Figure 4.7 Concrete cube exposed to two percent solution strength of sulfuric acid


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Figures 4.8 to 4.10 show the response of control and metakaolin concrete immersed in 5%

sulfuric acid solution. The curves clearly show that the metakaolin concrete performed

better at all ages in comparison with the control concrete. The degradation level was found

to be more in case of five percent solution strength than two percent solution strength. The

trend remained similar to that of two percent solution strength specimens. It can be

observed from the curves that higher metakaolin-binder ratios make concrete more resistant

to acid attack. This phenomenon was found applicable to all water-binder ratios as well as

to variable solution strengths of sulfuric acid.

Figure 4.11 Concrete cube exposed to five percent solution strength of sulfuric acid

Figure 4.11 shows the condition of a concrete cube when exposed to five percent solution

of sulfuric acid. In this case the destruction level of acid extends more than the surface of

the cube and at few places, the gravel pops out of the cube. The degradation takes place

both in metakaolin concrete and control concrete but the level of degradation was found

less in metakaolin concrete than that of control concrete.


73



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Figure 4.15 Concrete cube exposed to eight percent solution strength of sulfuric acid

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The degradation of concrete cubes exposed to eight percent sulfuric acid solution is shown

in Figure 4.15. At this concentration level the acid has completely eaten up the cement

around the aggregate which resulted in popping of aggregates out of cubes. It also reduces

the size of the cubes. It was noted that size of the concrete cubes with high water-binder

ratios had been reduced to half than compared to the size of concrete cubes with low water-

binder ratios immersed in acid bath of eight percent sulfuric acid solution. The concrete

cubes containing variable metakaolin-binder ratios showed similar type of destruction

patterns but the extent of destruction was lower which was eminent from the compressive

strengths of the cubes given in Table 4.11. Figures 4.12 to 4.14 represent the response of

control and metakaolin concrete immersed in sulfuric acid of eight percent solution

strength. The curves clearly showed that the metakaolin concrete performed better at all the

ages in comparison with the control concrete. The degradation level was found to be more

in case of eight percent solution strength than two and five percent solution strength. The

trend remains similar to that of five percent solution strength specimens. However the slope

of curves further increases than that of five percent solution strength specimens. It has also

been observed from the curves that higher metakaolin-binder ratios makes concrete more

resistant to acid attack. This phenomenon was found applicable for all water to binder

ratios.

4.4.3 Resistance to Acetic Acid

After twenty eight days of curing the specimens were transferred to the Acetic acid of

variable solution strength. The solution strengths used in this study were 2%, 5% and 8%.

The specimens were taken out of acid solution at their testing age and allowed to dry. The

compressive strength was determined for cubes from each mixture immersed in acid

solution of particular strength at 7, 28, 91 and 182 days. The compressive strength was

determined for each specimen and their average strengths are presented in tabular form in

Table 4.12 to 4.14. The results are also shown graphically.


76

Table 4.12 Average compressive strength for cubes immersed in 2% acetic acid


Strength (28 day)

Compressive strength after immersion period in acids (MPa)

7-day 28-day 91-day 182 day 300M00W45A02 40.8 40.96 41.47 43.10 45.32 300M15W45A02 47.78 48.02 48.72 50.98 54.54 300M20W45A02 46.35 46.65 47.61 50.84 55.50 300M25W45A02 40.07 40.58 41.73 45.56 51.20 300M00W55A02 36.2 36.24 36.42 37.21 38.44 300M15W55A02 43.13 43.30 43.57 44.89 46.65 300M20W55A02 40.54 40.64 41.34 43.30 46.33 300M25W55A02 36.81 37.21 38.19 41.34 46.24 300M00W65A02 31.70 31.71 31.73 31.74 31.85 300M15W65A02 38.6 38.69 38.81 39.31 40.00 300M20W65A02 34.85 35.05 35.34 36.36 37.64 300M25W65A02 33.8 33.99 34.81 37.58 41.51



Strength (28 day)




77



Strength (28 days)



Table 4.12 to 4.14 contains the compressive strength results for specimens immersed in

2%, 5% and 8% solution strengths of acetic acid. The strength decreases with age for all the

mixtures except for the specimens immersed in 2% solution. However an increase in

compressive strength results was observed with increase in metakaolin-binder ratio in

comparison to control mixtures. This aspect is clarified from the graphical information of

above results presented below.


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Figure 4.19 Concrete cube exposed to two percent solution strength of acetic acid

Figure 4.19 shows concrete cube subject to two percent solution strength of acetic acid. The

above picture does not show any sign of degradation of concrete and similar is true from

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the compressive strength results. Figures 4.16 to 4.18 represent the response of control and

metakaolin concrete immersed in acetic acid of two percent solution strength. The curves

clearly show that the metakaolin concrete performs better at all the ages in comparison with

the control concrete. Acetic acid is a weak acid and at low concentration it does not

produce any harmful effect on the concrete as observed in Figure 4.19 as well. At low

concentration the specimens were cured for extended curing period, therefore, resulted in

the increase in strength of metakaolin and control concrete. This also indicates that two

percent acetic acid solution strength does not have the power to break the bond of concrete

and eat up the respective compounds.


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Figures 4.20 to 4.22 represent the response of control and metakaolin concrete immersed in

acetic acid of five percent solution strength. The response of metakaolin and control

concrete is similar to that of specimens immersed in solution strength of two percent. At

five percent concentration level of acetic acid, the specimens showed increased strength for

lower water-binder ratios from their base line strength at twenty eight days. However at

higher water-binder ratios this trend was found to be negative. The rate of degradation was

not very prominent for the specimens immersed in five percent concentration level of acetic

acid. Few chunks have been found to be removed out of the specimens after 182 days of

immersion as shown in Figure 4.23.

Figure 4.23 Concrete cube exposed to five percent solution strength of acetic acid


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Figure 4.27 Concrete cube exposed to eight percent solution strength of acetic acid

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85


acetic acid of eight percent solution strength. The curves indicate that at higher

concentrations of acetic (weak) acid, it performs similar to that of strong acid. However the

degradation of concrete is in a different way as it does not eat up the cement rather it

degrades concrete by making the top surface softer which is removed later on in the form of

chunks of concrete shown in Figure 4.27. Hence it causes spalling of concrete contrary to

the sulfuric acid which eats up the cement and deteriorates the bond between binder and

aggregates thus reducing the compressive strength. Higher concentrations of acetic acid do

not degrade concrete to an extent to which it is degraded in case of sulfuric acid. Therefore,

the reduction in compressive strength for exposure in acetic acid is much less in

comparison to that of sulfuric acid.

4.4.4 Resistance to Carbonation The mixtures were casted according to the procedure outlined in Figure 4.1. Carbonation

samples with variable metakaolin-binder ratios and water-binder ratios along with the

control specimens were placed in open atmosphere for fifty two weeks after twenty eight

days of curing. Carbonation depth was determined by cutting the cube from middle and

then running the phenolphthalein indicator. Carbonation depth is measured from outer

edges towards inner side of the cube as shown in Figure 4.27.

Figure 4.27 Carbonation depth measurement for concrete cube


86

The carbonation depth was measured at an interval of four, seven, thirteen, twenty five and

fifty two weeks and given in Table 4.15

Table 4.15 Average carbonation depth of cubes subjected to open atmosphere

Mixture ID Carbonation depth (mm)

04-week 07-week 13-week 25-week 52-week 300M00W45C 0 0 0 1 3.5

300M15W45C 0 0 0 0 3.5

300M20W45C 0 0 0 0 3

300M25W45C 0 0 0 0 3

300M00W55C 0 0 0.5 1.5 5.5

300M15W55C 0 0 0 0 4

300M20W55C 0 0 0 0 3.5

300M25W55C 0 0 0 0 3

300M00W65C 0 0 2.5 4.5 10

300M15W65C 0 0 0 4 8.5

300M20W65C 0 0 0 3 5.5

300M25W65C 0 0 0 2 5.5

Carbonation depth is presented graphically in Figure 4.28. Carbonation started in control

concrete after thirteen and twenty five week duration. Carbonation also depends on water-

binder ratios i.e. increased water-binder ratio lead to early carbonation while decreased

water-binder ratios leads to slow carbonation process. Figure 4.28 clearly indicates that the

carbonation depth decreases as water-binder ratio decreases. Carbonation depth also

decreases with an increase in metakaolin binder ratio but found to be almost similar for

twenty and twenty five percent metakaolin-binder ratios. This phenomenon is attributed to

the fact that inclusion of metakaolin alters the pore structure of metakaolin concrete and

after twenty percent of replacement level there is no significant change in porosity of the


87

mixture. Therefore metakaolin-binder ratio is effective up to twenty percent beyond which

it becomes almost ineffective against carbonation control.

Figure 4.28 Carbonation depth for binder content 300 kg/m3

4.5 TEST RESULTS FOR BINDER CONTENT 400 kg/m3

The mixtures were casted according to the procedure outline in Figure 4.2. Compressive

strength of the cubes were determined according to ASTM 109/C and recorded in tabular

form.

4.5.1 Strength of Metakaolin concrete

The compressive strength of the mixtures was determined after seven and twenty eight days

of curing. The specimens were taken out of curing tank, wiped and placed in open

atmosphere for drying before determining their compressive strength. The compressive

strength results for control and metakaolin concrete are presented in Table 4.16.

0

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00W

45

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Sample Designation

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Table 4.16 Average compressive strength for cubes

Mixture ID Mix proportions by weight Compressive

Strength (MPa)

Cement Metakaolin Sand Gravel Water 7 - day 28- day

400M00W45 1 0 1.48 2.96 0.45 35.33 47.00

400M15W45 0.85 0.15 1.48 2.96 0.45 41.08 54.00

400M20W45 0.80 0.20 1.48 2.96 0.45 36.36 47.8

400M25W45 0.75 0.25 1.48 2.96 0.45 31.65 41.6

400M00W55 1 0 1.4 2.8 0.55 28.13 36.97

400M15W55 0.85 0.15 1.4 2.8 0.55 34.66 45.56

400M20W55 0.80 0.20 1.4 2.8 0.55 30.32 39.85

400M25W55 0.75 0.25 1.4 2.8 0.55 27.22 35.78

400M00W65 1 0 1.3 2.6 0.65 21.30 28.00

400M15W65 0.85 0.15 1.3 2.6 0.65 28.64 37.64

400M20W65 0.80 0.20 1.3 2.6 0.65 24.60 32.34

400M25W65 0.75 0.25 1.3 2.6 0.65 23.14 30.41

The tabular values presented in Table 4.16 are also plotted graphically in Figure 4.29. The

results clearly indicate that maximum pozzolanic activity was observed when the

metakaolin-binder ratio is fifteen percent. This study deals with the durability

determination of metakaolin concrete for variable metakaolin-binder ratios. Therefore

twenty eight day results will be used as a reference for determination of durability of

concrete.


89

Figure 4.29 Compressive strength at twenty eight days

4.5.2 Resistance to Sulfuric Acid

After twenty eight days of curing the specimens were transferred to the sulfuric acid of

variable solution strength. The solution strengths used in this study were 2%, 5% and 8%.

The specimens were taken out of acid solution at their specific age and allowed to dry. The

compressive strength was determined for cubes from each mixture immersed in acid

solution of particular strength at 7, 28, 91 and 182 days. The average compressive strengths

were for cubes and results are presented in Table 4.17 to 4.19. For each acid exposure the

compressive strengths were also plotted graphically against duration for fixed water-binder

ratios.

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Strength (28 days)


7-days 28-days 91-days 182 days

400M00W45S02 47.00 46.65 45.56 42.25 37.82

400M15W45S02 54.00 53.58 52.71 49.70 45.56

400M20W45S02 47.8 47.47 46.65 43.96 40.32

400M25W45S02 41.6 41.28 40.58 38.07 34.69

400M00W55S02 36.97 36.72 35.70 32.89 29.05

400M15W55S02 45.56 45.16 43.96 40.58 35.88

400M20W55S02 39.85 39.56 38.56 35.76 31.92

400M25W55S02 35.78 35.52 34.69 32.26 28.84

400M00W65S02 28.00 27.83 27.04 24.90 21.90

400M15W65S02 37.64 37.33 36.36 33.64 29.70

400M20W65S02 32.34 32.09 31.36 29.38 26.52

400M25W65S02 30.41 30.14 29.48 27.41 24.50



Strength (28 days)




91



Strength (28 days)



Careful analysis of table 4.17 to 4.19 shows the decrease in compressive strength of cubes

for extended exposure of variable acid strength of sulfuric acid. However the actual

performance of metakaolin concrete can be explained with the help of curves presented

below.


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sulfuric acid of two percent solution strength. The curves indicate that the metakaolin

concrete performs better at all the ages in comparison with the control concrete. The twenty

eight day compressive strength for higher metakaolin-binder ratios was although less than

that of control concrete, but, at increased metakaolin-binder ratios the metakaolin concrete

performed remarkably as comparison to that of control concrete for 2% exposure of sulfuric

acid. Increase in water to binder ratio decreases the strength for both control and

metakaolin concrete which is eminent from the slope of the curves.

The visual view of concrete exposed to two percent sulfuric acid is given in Figure 4.33.

The deterioration for two percent exposure is much less but slightly more than the cubes

with binder content 300 kg/m3. The deterioration affects the surface of the cube by eating

up very thin layer of cement when exposed to extended duration inside acids.

Figure 4.33 Concrete cube exposed to two percent solution strength of sulfuric acid


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sulfuric acid of five percent solution strength. The curves clearly show that the metakaolin

concrete performs better at all ages in comparison with the control concrete. The

degradation level was found to be more in case of five percent solution strength than two

percent solution strength. The trend remains similar to that of two percent solution strength

specimens. However, the slope of curves which was almost linear in case of specimens

exposed to two percent solution now changes slightly to more than one. It has also been

observed from the curves that higher metakaolin-binder ratios makes concrete more

resistant to acid attack however the rate of attack increases with increase in concentration

of acid. This phenomenon was found applicable for all water to binder ratios.

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Figure 4.37 Concrete cube exposed to five percent solution strength of sulfuric acid

Figure 4.37 present the condition of a concrete cube when exposed to five percent solution

of sulfuric acid. In this case the destruction level of acid extends deeper than the surface of

the cube and at few places, the gravel pops out of the cube. The degradation in the binder

content of 400 kg/m3 was found to be more than that of 300 kg/m3 binder content. This

phenomenon is attributed to the fact that increase in cement content produces more calcium

hydroxide. The higher amount of calcium hydroxide makes concrete more vulnerable to

acid attack and hence its resistance to acid attack is decreased. The degradation for the

cubes increases for variable metakaolin-binder content but remains less than that of control

concrete. It has been also observed that at cement-binder ratio of twenty five percent, the

metakaolin concrete showed remarkably good results in resisting the acid attacks.


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Figure 4.41 Concrete cube exposed to eight percent solution strength of sulfuric acid

Degradation for cubes when exposed to eight percent solution strength of sulfuric acid is

shown in Figure 4.41. The size of the cube was reduced at eight percent solution of sulfuric

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acid. Acid eats up the binder around the coarse aggregate which results in loosening of

coarse aggregate first and then being washed away from the cube. This phenomena results

in the reduction of the size of cube. Concrete cubes with higher water to binder ratios were

generally eaten up by more than half for control mixtures. The concrete cubes containing

variable metakaolin-binder ratios showed similar type of destruction patterns but the extent

of destruction was lower which is eminent from the compressive strengths of the cubes

given in Table 4.19. Figures 4.38 to 4.40 represent the response of control and metakaolin

concrete immersed in sulfuric acid of eight percent solution strength. The increase in

solution strength increases the deterioration of concrete. The curves clearly show that the

metakaolin concrete performs better at all the ages in comparison with the control concrete.

The degradation level was found to be higher in case of eight percent solution strength than

two and five percent solution strength. The trend remains similar to that of five percent

solution strength specimens. However the curvature of curves further increases than that of

five percent solution strength specimens. It has also been observed from the curves that

higher metakaolin-binder ratios makes concrete more resistant to acid attack. This

phenomenon was found applicable to all water-binder ratios.

4.5.3 Resistance to Acetic Acid

In case of 400 kg/m3 cement content, same procedure was adopted for the immersion of

cubes into weak acids as the case for 300 kg/m3 cement content i.e. after twenty eight days

of curing the specimens were transferred to the Acetic acid of variable solution strength of

2%, 5% and 8%. The specimens were taken out of acid solution and allowed to dry before

carrying out the compressive test. The compressive strength was determined for each

mixture cubes immersed in acid solution of particular strength at 7, 28, 91 and 182 days.

The average compressive strengths obtained at each testing age after specific immersion

type is presented in Table 4.20 to 4.22. The results are also plotted graphically for fixed

water-binder ratios against immersion time.


100



Strength (28 day)


7-day 28-day 91-day 182 day 400M00W45S02 47.00 47.2 47.89 49.98 53.1 400M15W45S02 54.00 54.02 54.61 55.95 57.76 400M20W45S02 47.8 48.16 49 51.84 55.98 400M25W45S02 41.6 41.86 42.9 45.56 49.33 400M00W55S02 36.97 37.09 37.45 38.44 39.94 400M15W55S02 45.56 45.43 45.29 45.23 45.16 400M20W55S02 39.85 40.07 4045 41.73 43.56 400M25W55S02 35.78 36 36.60 38.19 40.58 400M00W65S02 28.00 28.1 28.30 28.84 29.46 400M15W65S02 37.64 37.33 37.09 35.76 33.8 400M20W65S02 32.34 32.49 32.60 33.18 33.8 400M25W65S02 30.41 30.58 31.02 32.26 33.8



Strength (28 day)


7-day 28-day 91-day 182 day 400M00W45S05 47.00 46.79 46.65 46.24 45.37 400M15W45S05 54.00 53.58 53.14 50.98 48.26 400M20W45S05 47.8 47.61 47.47 46.79 45.87 400M25W45S05 41.6 41.73 41.99 42.64 43.61 400M00W55S05 36.97 36.78 36.36 35.16 33.64 400M15W55S05 45.56 45.29 44.56 42.25 38.94 400M20W55S05 39.85 39.68 39.19 37.58 35.48 400M25W55S05 35.78 35.88 36.0 36.3 36.60 400M00W65S05 28.00 27.88 27.25 25.81 23.65 400M15W65S05 37.64 37.33 36.60 34.22 30.89 400M20W65S05 32.34 31.98 31.36 29.38 26.83 400M25W65S05 30.41 30.25 30.14 30.03 29.92


101



Strength (28 days)


7-day 28-day 91-day 182 day 400M00W45S08 47.00 46.51 45.29 41.86 37.19 400M15W45S08 54.00 53.29 51.7 46.51 39.58 400M20W45S08 47.8 47.54 46.79 43.96 40.54 400M25W45S08 41.6 41.34 40.83 38.81 36.23 400M00W55S08 36.97 36.31 35.16 31.42 26.54 400M15W55S08 45.56 44.89 43.16 37.82 30.91 400M20W55S08 39.85 39.56 38.44 35.52 31.36 400M25W55S08 35.78 35.52 34.87 33.41 30.89 400M00W65S08 28.00 27.67 26.21 22.56 17.64 400M15W65S08 37.64 37.09 35.16 29.70 22.94 400M20W65S08 32.34 32.04 31.02 27.67 23.35 400M25W65S08 30.41 30.20 29.81 28.09 26.01

Table 4.20 to 4.22 contains the compressive strength results for specimens immersed in

2%, 5% and 8% solution strengths of acetic acid. The strength decreases with age for all the

mixtures except for the specimens immersed in 2% solution. Increase in case of two percent

acetic acid solution was primarily due to the reason that it is a weak acid, hence the

immersion period counts in the curing of the specimens. This trend was obtained not only

for metakaolin concrete specimens but also for the control specimens as well. However the

trend of acetic acid attack was found similar as that in case of sulfuric acid. The above

results have also been plotted for each solution strength graphically which are given below.


102



0.00

10.00

20.00

30.00

40.00

50.00

60.00

0 50 100 150 200

Com

pres

sive

Str

engt

h(M

Pa)


400M00W45A02400M15W45A02400M20W45A02400M25W45A02

0.00

10.00

20.00

30.00

40.00

50.00

60.00

0 50 100 150 200

Com

pres

sive

Str

engt

h(M

Pa)


400M00W55A02400M15W55A02400M20W55A02400M25W55A02


103

Figure 4..44 Deterioration of compressive strength at water-binder ratio = 0.65

Figure 4.45 Concrete cube exposed to two percent solution strength of acetic acid

Figure 4.45 shows concrete cube subject to two percent solution strength of acetic acid. The

above picture does not show any sign of degradation of concrete and similar is true from

0.00

10.00

20.00

30.00

40.00

50.00

60.00

0 50 100 150 200

Com

pres

sive

Str

engt

h(M

Pa)


400M00W65A02400M15W65A02400M20W65A02400M25W65A02


104

the compressive strength results. Figures 4.42 to 4.44 represent the response of control and

metakaolin concrete immersed in acetic acid of two percent solution strength. The curves

clearly show that the metakaolin concrete performs better at all the ages in comparison with

the control concrete. Acetic acid is a weak acid and at low concentration it does not

produce any harmful effect on the concrete as observed in Figure 4.45 as well. At low

concentration the specimens were cured for extended curing period, therefore, resulted in

the increase in strength of metakaolin and control concrete. Initially the compressive

strength of the metakaolin concrete was more; therefore similar type of patter was obtained

in the curves as well. The results also points towards the fact that two percent acetic acid

solution strength does not have the power to break the bond of concrete and eat up the

respective compounds. At high water-binder ratios, concrete with higher cement-binder

ratios were found to perform well. However at lower water-binder metakaolin concrete

behaves similar to that of the control concrete when immersed in two percent acetic acid

solution.


0.00

10.00

20.00

30.00

40.00

50.00

60.00

0 50 100 150 200

Com

pres

sive

Str

engt

h(M

Pa)


400M00W45A05400M15W45A05400M20W45A05400M25W45A05


105



0.00

10.00

20.00

30.00

40.00

50.00

60.00

0 50 100 150 200

Com

pres

sive

Str

engt

h(M

Pa)


400M00W55A05400M15W55A05400M20W55A05400M25W55A05

0.00

10.00

20.00

30.00

40.00

50.00

60.00

0 50 100 150 200

Com

pres

sive

Str

engt

h(M

Pa)


400M00W65A05400M15W65A05400M20W65A05400M25W65A05


106

Figure 4.49 Concrete cube exposed to five percent solution strength of acetic acid


acetic acid of five percent solution strength. The response of metakaolin and control

concrete is similar to that of specimen’s immersed in sulfuric acid but the degradation is

less or loss of strength is not very high as the case for cubes exposed to five percent

solution strength of sulfuric acid. Few chunks have been found to be removed out of the

specimens after 182 days of immersion as shown in Figure 4.49. It has also been observed

that an increased metakaolin-binder ratio performs more positively in resisting the attack of

acid at higher water-binder ratios.


107



0.00

10.00

20.00

30.00

40.00

50.00

60.00

0 50 100 150 200

Com

pres

sive

Str

engt

h(M

Pa)


400M00W45A08400M15W45A08400M20W45A08400M25W45A08

0.00

10.00

20.00

30.00

40.00

50.00

60.00

0 50 100 150 200

Com

pres

sive

Str

engt

h(M

Pa)


400M00W55A08400M15W55A08400M20W55A08400M25W55A08


108


Figure 4.53 Concrete cube exposed to eight percent solution strength of acetic acid

0.00

10.00

20.00

30.00

40.00

50.00

60.00

0 50 100 150 200

Com

pres

sive

Str

engt

h(M

Pa)


400M00W65A08400M15W65A08400M20W65A08400M25W65A08


109

Figures 4.50 to 4.52 present the behavior of concrete with variable metakaolin-binder and

water-binder ratios when exposed to eight percent solution strength of acetic acid. The

curves clearly indicate that high dose of metakaolin or at higher metakaolin– binder ratios it

resists the acid attack very effectively. The resistance increases with increase in water to

binder ratios or it is more effective at higher water-binder ratios than at lower water-binder

ratios. The curves also indicate that at higher concentrations of acetic (weak) acid, it

performs similar to that of sulfuric acid. However the degradation of concrete is in a

different way as it does not eat up the cement rather it degrades concrete by making the top

surface softer which is removed later on in the form of chunks of concrete shown in Figure

4.53. Hence it causes spalling of concrete contrary to the sulfuric acid which eats up the

cement and deteriorates the bond between binder and aggregates thus reducing the

compressive strength. Higher concentrations of acetic acid do not degrade concrete to an

extent to which it is degraded in case of sulfuric acid. Therefore, the reduction in

compressive strength for acetic acid is less in comparison to that of sulfuric acid.

4.5.4 Resistance to Carbonation The mixtures were casted according to the procedure outlined in Figure 4.2. Carbonation

samples with variable cement-binder ratios and water-binder ratios along with the control

specimens were placed in open atmosphere for fifty two weeks after twenty eight days of

curing. Carbonation depth was determined by cutting the cube from middle and then

running the phenolphthalein indicator. Carbonation depth is measured from outer edges

towards inner side of the cube as shown in Figure 4.54.

Figure 4.54Carbonation depth measurement for concrete cube


110

The carbonation depth was measured at an interval of four, seven, thirteen, twenty five and

fifty two weeks and given in Table 4.23.

Table 4.23 Average carbonation depth of cubes subjected to open atmosphere

Mixture ID Carbonation depth (mm)

04-week 07-week 13-week 25-week 52-week 400M00W45 0 0 0 1.5 2

400M15W45 0 0 0 0 1

400M20W45 0 0 0 0 1.5

400M25W45 0 0 0 1 2

400M00W55 0 0 0.5 1.5 3.5

400M15W55 0 0 0 0 0.5

400M20W55 0 0 0 0.5 2.5

400M25W55 0 0 0 0.5 2.5

400M00W65 0 0 2 5.5 6

400M15W65 0 0 0 2 3

400M20W65 0 0 0 2 3.5

400M25W65 0 0 0 2.5 4

Carbonation depth is presented graphically in Figure 4.55. The control and metakaolin

concrete did not show any carbonation after the lapse of four and seven week duration.

Carbonation was observed in control concrete after thirteen week with higher water-binder

ratios. Carbonation depth was found to be less for lower water-binder ration and increases

with increase in water-binder ratios. The metakaolin concrete developed carbonation after

twenty five week. At lower metakaolin binder ratios the carbonation depth was less but

becomes almost constant for twenty and twenty five percent metakaolin-binder ratios. The

carbonation depth was found to be less in magnitude for 400 kg/m3 binder content when

compared with 300 kg/m3 binder content. It is interesting to note that concrete with 400

kg/m3 binder content is less resistant to acid attack whereas its resistance to carbonation is

enhanced in comparison to concrete made with 300 kg/m3 binder content. This


111

phenomenon is attributed to the fact that increase in binder content decreases the porosity,

thus making the concrete more resistant to carbonation.


4.6 SUMMARY

The response of metakaolin concrete was determined for acid attack and carbonation effect

against variable metakaolin-binder ratios and water-binder ratios. There were total twenty

four mixtures from two different binder contents of 300 and 400 kg/m3. The response of

metakaolin concrete against two acids (Sulfuric and Acetic) was determined over a period

of 182 days and the results were compared with control concrete.

Metakaolin concrete found to be very effective against the acid resistance of concrete

especially at higher water-binder ratios. Higher concentrations of weak (Acetic) acid

behave similar to that of strong (Sulfuric) acid. While low concentrations of weak (Acetic

acid) does not have any harmful effect on the concrete rather it extends the curing of

concrete.

0

1

2

3

4

5

6

7

400M

00W

45

400M

15W

45

400M

20W

45

400M

25W

45

400M

00W

55

400M

15W

55

400M

20W

55

400M

25W

55

400M

00W

65

400M

15W

65

400M

20W

65

400M

25W

65

Sample Designation

Car

bona

tion

dept

h(m

m)



112

Carbonation depth was determined after four, seven, thirteen, twenty five and fifty two

weeks. The carbonation study was spanning over a year. Carbonation studies revealed that

metakaolin concrete also provide sufficient resistance against carbonation. The effect of

carbonation is not eliminated in case of metakaolin concrete rather it slows down when

metakaolin is incorporated with cement in comparison to that of control concrete.

Carbonation increases with increase in water-binder ratios both for control and metakaolin

concrete.

CHAPTER-5

113

DEVELOPMENT OF MODEL

5.1 INTRODUCTION

The metakaolin developed from kaolin clay from Nagar Parker was used to cast 24

concrete mixtures by combining 2 binder contents with 4 metakaolin–binder ratios and 3-

water-binder ratios. The specimens were subjected to 28-day standard moist curing and

were immerse in acidic solutions of variable concentrations. A weak and a strong acid were

used in experimentation. The concrete specimens were crushed to failure after 7, 28, 91 and

182 days of immersion. The details and discussions of experimental program have been

presented in Chapter 4. Outlines of a basic model for predicting strength of concrete

subjected to acid attack has been presented in this chapter.

5.2 THE MODEL

It may be noted that a metakaolin processed from a single source was used to make

concretes with a single Ordinary Portland Cement. The development of model will be

subjected to this limitation. It is not possible to identify the role of Bogue's Compounds

from cement or major oxides from metakaolin because data from a variety of sources were

not available. A statistical approach has been adopted to predict the loss of strength. The

major parameters of the model are limited to binder content B, metakaolin-binder ratio, rM,

water-binder ratio rW, solution strength S, and period of immersion in acid solution t. The

strength of concrete after immersion of t-days in acid solution, 'tf is related with reference

to 'cf , the 28-day strength of concrete as follows:

' ' 't c tf f f= + ∆ (5.1)

Where 'tf∆ denotes the loss of strength after immersion of t days in acidic solution. The

strength of specimens cast from various mixtures after immersion of 0, 7, 28, 91 and 182

days in acid solution of different concentrations have been plotted in Figures 5.1 and 5.2. It

may be depicted from these figures that strength vs. immersion period plots are represented

fairly by straight lines. Therefore, it is proposed that loss of strength is directly proportional

to immersion period t and the relationship may be written as given in the following:

' 't tf f tδ∆ = (5.2)

CHAPTER-5 DEVELOPMENT OF MODEL

114

Where 'tfδ is rate of strength loss at immersion period t. It may be seen from these figures

that the slopes of strength vs. immersion period curves of concrete cast with different

mixture proportions are different while subjected to acid solution of same concentration.

The main variables in the test program were metakaolin-binder ratio rM, water-binder ratio

rW, binder content B, and solution strength S. Hence as a first assessment it is assumed that

strength loss depends upon on all these variables namely rM, rW, B and S. The assumption is

examined and justified in the following paragraphs for each of the four variables.

That the strength loss is dependent upon rM can be verified from the comparison of slopes

of three curves on each of the Figures 5.3 (a) to (f). Each of the six charts of this Figure

depicts strengths vs. immersion period plots of three concretes of otherwise similar mixture

proportion except metakaolin-binder ratio which is varied and they all are subjected to acid

attack of same strength. The sharp contrast of slopes of these curves clearly indicates that

rM plays an important role in imparting the strength loss.

It is assumed that water-binder ratio rW is another variable that affects the loss of strength in

its own way. The strength loss has been plotted against immersion period in Figures 5.1 and

5.2. Here strengths of concretes with same composition but with variable water-binder ratio

have been grouped in six charts on each of the two figures. It may be verified that the

slopes of three curves on each of the twelve charts shown in Figures 5.1 and 5.2 are

different. The three curves on Figure 1(a), for example, belong to concretes

300M15WwwS05; i.e., the only variable in three curves is water-binder ratio rW. .The

slopes of the three curves are quite different. This finding is corroborated from the other 11

charts of the two figures. The assumption that strength loss is also a function of rW is well

justified from the careful examination of these plots.

Does the acid solution strength S also influence the rate of strength loss? The answer to this

question can be found by inspecting the plots shown in Figure 5.4. The three curves on

Figure 5.4(a), for example, show that the slope of strength curves of concretes of identical

mixtures is different when subjected to solutions of different concentrations. This finding is

further confirmed by the Figures 5. 4(b) to 5.4(f) which justifies the assumption that

strength loss is affected by the solution strength as well.

What is role of binder content B in strength loss of concrete when subjected to acid attack?

The answer may be found from the Figure 5.5 (a) to (f). Each of the figures (a) to (f) have

been plotted with strength loss vs. immersion period for concretes of identical mixture


115

proportions cast with two different binder contents 300 kg/m3and 400 kg/m3 of concrete.

The sharp difference of slopes of strength curves of concrete made from the two different

binder contents has been noted from these figures, which shows that strength loss is also

affected by the binder content.

In view of the discussion made in the four preceding paragraphs the loss of strength may be

written in functional form as follows:

' ( , , , , ( ))t M Wf F r r B S E tδ = (5.3)

Where E(t) has been included as a penalty function to limit the error in rate which may

otherwise grow with period of immersion t. In the next stage of the formulation it is

necessary to identify the way the loss of strength depends upon each of the five parameters

specified in the above equation so that the loss of strength may be expressed explicitly as

suitable polynomials of these variables.

5.2.1 Variation of strength loss with rM

In order to identify the role of rM the strength is plotted against rM in Figure 5.6 where as

strength loss vs. rM plot is provided in Figure 5.7. A close inspection of the curves on these

two Figures reveals that only a cubic polynomial of rM may well interpolate the strength as

well as the strength loss at a given rM value. Hence it is proposed that rate of strength loss

may be expressed by a cubic polynomial of metakaolin-binder ratio rM.

5.2.2 Variation of strength loss with rW

It is well established fact that the porosity of concrete is sharply influenced by water-binder

ratio of a mixture. The porosity in turn plays an important rule against acid attack. The

higher the porosity the higher would be the strength loss at a given immersion period. This

general fact has been well confirmed by the experimental data obtained from this research.

Working on the same lines as described in the preceding section the strength loss has been

plotted against the three water-binder ratios and typical plots have been grouped in Figure

8. It may be noted that variation of strength loss due to rW is less sharp than that with rM as

was concluded in the section 5.2.1, therefore a quadratic polynomial of rW has been

proposed to interpolate the variation of strength loss due to water-binder ratio.


116

5.2.3 Variation of strength loss with B and S

In order to identify the type of interpolators the best suited for B and S, the plots of Figures

5.3, 5.4, 5.5 and 5.10 are to be examined simultaneously. One fact is established beyond

doubt from these plots that the characteristics of the curves for identical mixture

proportions are quite different when subjected to acid attack of different strengths. Same is

true about the nature of strength curves when only binder content is kept as the sole

variable. Most of the curves shown in Figure 5.10 are more or less quadratic in nature

where as a limited number of curves are almost linear which is an indication that B and S

interact with each other and also with rM and rW.

In view of all the discussion made in previous sub-sections, it is proposed that the

functional from of the rate of loss of strength given by Equation 5.3 may be noted by the

following expression:

3 2'

1 1( , ) ( , ) ( , ) log( )i i

t i M i Wf B S r B S r B S tδ α β γ= + +∑ ∑ (5.4)

Where the coefficients , and i iα β γ are functions of B and S only. It may be denoted that

the penalty function E(t) has been modeled as a function of log(t), because error does not

grow linearly with time. The functional relationships for the three sets of coefficients

, and i i iα β γ are given in the following:

31

1( , ) ( ) j

i i jB S a B Sα −= ∑ (5.5a)

31

1

( , ) ( ) ji i j

j

B S b B Sβ −

=

= ∑ (5.5b)

31

1

( , ) ( ) jjB S c B Sγ −= ∑ (5.5c)

In developing the above relationships it has been assumed that the three sets of coefficients

, , and i i iα β γ vary as quadratic function of solution strength S, and the corresponding

weight functions , and ij ij ja b c depend only upon binder content B. This has been based on

the mixed nature of strength loss curves shown in Figure 5.10 and in view of the discussion

noted in section 5.2.3. More over a quadratic polynomial can accurately interpolate the data


117

through three points as only three strengths 2%, 5% and 8% have been used in the present

experimental program. The selection of linear interpolation for binder content is dictated by

the fact that data from only two binder contents are available,

The coefficients , and ij ij ja b c will be determined by multiple regression analysis from

data of two classes of concrete cast by different binder content, hence a Lagrange

interpolation of first order is proposed between B=300 kg/m3 and 400 kg/m3 i.e.,

300 300 400 400( ) ( ) ( )ij ij ija B a N B a N B= + (5.6a)

300 300 400 400( ) ( ) ( )ij ij ijb B b N B b N B= + (5.6b)

300 300 400 400( ) ( ) ( )j j jc B c N B c N B= + (5.6c)

It may be noted that the coefficients 300 400 300 400 300 400, , , , ,ij ij ij ij j ja a b b c c would be found by

calibration of the model from the data of 300 kg/m3 and 400 kg/m3 class concretes. The two

interpolation functions N300 and N400 are the first order Lagrange interpolators as given in

the following:

300 400 300( ) 1300 400 100B BN B − −

= = −−

(5.6d)

400 300 300( )400 300 100B BN B − −

= =−

(5.6e)

The final model in view of the foregoing Equations 5.1 to 5.6 may be written in the vector

form as in the following:

' ' [ log( )]t c M Wf f r aS r bS cS t t= + + +% %% % % % % %

(5.7)

The various vectors and matrices involved in the above equation are given in the following

one by one.

Both Mr% and Wr%%

are Ritz vectors of order 3 and 2 respectively and may be written as:

2 3[ ]M M M Mr r r r=%

(5.7a)

2[ ]W W Wr r r=%

(5.7b)


118

The coefficient matrix a%

is a square matrix of order 3 and b%

is a rectangular matrix of size

3x2.

11 12 13

21 22 23

31 32 33

a a aa a a a

a a a

⎡ ⎤⎢ ⎥= ⎢ ⎥⎢ ⎥⎣ ⎦

% (5.7d)

11 12 13

21 22 23

b b bb

b b b⎡ ⎤

= ⎢ ⎥⎣ ⎦%

(5.7e)

It may be noted that c%

is a row vector with 3 components and the components of S%

make a

complete basis function of order two and both are written in the following:

[ ]1 2 3c c c c=%

(5.7f)

0

1

2 2

1SS S S

S S

⎡ ⎤ ⎡ ⎤⎢ ⎥ ⎢ ⎥= =⎢ ⎥ ⎢ ⎥⎢ ⎥ ⎢ ⎥⎣ ⎦⎣ ⎦

% (5.7g)


119

10

20

30

40

50

60

0 50 100 150 200

Immersion Period , days

Stre

ngth

, MPa

300M15W45S05300M15W55S05300M15W65S05

10

20

30

40

50

60

0 50 100 150 200


Stre

ngth

, MPa

400M15W45S05400M15W55S05400M15W65S05

(a) (b)

10

20

30

40

50

60

0 50 100 150 200Immersion Period , days

Stre

ngth

, MPa

300M20W45S05300M20W55S05300M20W65S05

10

20

30

40

50

60


Stre

ngth

, MPa

400M20W45S05400M20W55S05400M20W65S05

(c) (d)

10

20

30

40

50

60

0 50 100 150 200


Stre

ngth

, MPa

300M25W45S05300M25W55S05300M25W65S05

10

20

30

40

50

60

0 50 100 150 200


Stre

ngth

, MPa

400M25W45S05400M25W55S05400M25W65S05

(e) (f) Figure 5.1. Strength vs. Immersion Period in 5% Sulfuric Acid Solution


120

20

30

40

50

0 50 100 150 200


Stre

ngth

, MPa

300M15W45S02300M15W55S02300M15W65S02

30

40

50

60

0 50 100 150 200


Stre

ngth

, MPa

400M15W45S02400M15W55S02400M15W65S02

(a) (b)

20

30

40

50


Stre

ngth

, MPa

300M20W45S02300M20W55S02300M20W65S02

20

30

40

50


Stre

ngth

, MPa

400M20W45S02400M20W55S02400M20W65S02

(c) (d)

20

30

40

50

0 50 100 150 200


Stre

ngth

, MPa

300M25W45S02300M25W55S02300M25W65S02

20

30

40

50

0 50 100 150 200


Stre

ngth

, MPa

400M25W45S02400M25W55S02400M25W65S02

(e) (f)

Figure 5.2. Strength vs. Immersion Period in 2% Sulfuric Acid Solution


121

10

20

30

40

50

60

0 50 100 150 200


Stre

ngth

, MPa

300M15W45S05300M20W45S05300M25W45S05

10

20

30

40

50

60

0 50 100 150 200


Stre

ngth

, MPa

400M15W45S05400M20W45S05400M25W45S05

(a) (b)

10

20

30

40

50

60


Stre

ngth

, MPa

300M15W55S05300M20W55S05300M25W55S05

10

20

30

40

50

60


Stre

ngth

, MPa

400M15W55S05400M20W55S05400M25W55S05

(c) (d)

10

20

30

40

50

60

0 50 100 150 200


Stre

ngth

, MPa

300M15W65S05300M20W65S05300M25W65S05

10

20

30

40

50

60

0 50 100 150 200


Stre

ngth

, MPa

400M15W65S05400M20W65S05400M25W65S05

(e) (f)

Figure 5.3. Strength vs. Immersion Period in 5% Sulfuric Acid Solution


122

0

10

20

30

40

50

0 50 100 150 200


Stre

ngth

, MPa

300M15W45S02300M15W45S05300M15W45S08

0

10

20

30

40

50

60

0 50 100 150 200


Stre

ngth

, MPa

400M15W45S02400M15W45S05400M15W45S08

(a) (b)

20

30

40

50


Stre

ngth

, MPa

300M20W45S02300M20W45S05300M20W45S08

20

30

40

50


Stre

ngth

, MPa

400M20W45S02400M20W45S05400M20W45S08

(c) (d)

0

10

20

30

40

50

0 50 100 150 200


Stre

ngth

, MPa

300M25W45S02300M25W45S05300M25W45S08

0

10

20

30

40

50

0 50 100 150 200


Stre

ngth

, MPa

400M25W45S02400M25W45S05400M25W45S08

(e) (f)

Figure 5.4. Strength vs. Immersion Period plot of concretes placed in Sulfuric Acid Solutions of different concentrations


123

30

40

50

60

0 50 100 150 200


Stre

ngth

, MPa

300M25W45S02400M25W45S02

30

40

50

60

0 50 100 150 200


Stre

ngth

, MPa

300M20W45S02400M20W45S02

(a) (b)

20

30

40

50


Stre

ngth

, MPa

300M15W55S05

400M15W55S05

20

30

40

50

0 50 100 150 200


Stre

ngth

, MPa

300M20W55S05400M20W55S05

(c) (d)

10

20

30

40

0 50 100 150 200


Stre

ngth

, MPa

300M25W65S08400M25W65S08

10

20

30

40

0 50 100 150 200


Stre

ngth

, MPa

300M20W65S08

400M20W65S08

(e) (f)

Figure 5.5 Strength vs. Immersion Period for two Binder Contents


124

30

40

50

0 10 20 30

rM, %

Stre

ngth

, MPa

300W45S02300W55S02300W65S02

20

30

40

50

60

0 10 20 30

rM, %

Stre

ngth

, MPa

400W45S02400W55S02400W65S02

(a) (b)

25

35

45

0 10 20 30

rM, %

Stre

ngth

, MPa

300W45S05300W55S05300W65S05

20

30

40

50

60

0 10 20 30

rM, %

Stre

ngth

, MPa

400W45S05400W55S05400W65S05

(c) (d)

25

35

45

0 10 20 30

rM, %

Stre

ngth

, MPa

300W45S08300W55S08300W65S08

20

30

40

50

60

0 10 20 30

rM, %

Stre

ngth

, MPa

400W45S08400W55S08400W65S08

(e) (f)

Figure 5.6. Strength vs. M-B Ratio at 28 day Immersion in Sulfuric Acid


125

0

1

2

3

4

0 10 20 30

rM, %

Stre

ngth

Los

s, M

Pa300W45S02300W55S02300W65S02

0

0.5

1

1.5

2

0 10 20 30

rM, %

Stre

ngth

Los

s, M

Pa

400W45S02400W55S02400W65S02

(a) (b)

0

1

2

3

4

5

0 10 20 30

rM, %

Stre

ngth

Los

s, M

Pa

300W45S05300W55S05300W65S05

0

1

2

3

4

5

0 10 20 30

rM, %

Stre

ngth

Los

s, M

Pa

400W45S05400W55S05400W65S05

(c) (d)

0

4

8

0 10 20 30

rM, %

Stre

ngth

Los

s, M

Pa

300W45S08300W55S08300W65S08

0

4

8

0 10 20 30

rM, %

Stre

ngth

Los

s, M

Pa

400W45S08400W55S08400W65S08

(e) (f)

Figure 5.7. Loss of Strength vs. M-B Ratio at 28 day Immersion in Sulfuric Acid


126

0

1

2

40 50 60 70

rW, %

Stre

ngth

Los

s, M

Pa300M15S02300M20S02300M25S02

0

1

2

40 50 60 70

rW, %

Stre

ngth

Los

s, M

Pa

400M15S02400M20S02400M25S02

(a) (b)

0

1

2

3

4

40 50 60 70

rW, %

Stre

ngth

, MPa

300M15S02300M20S02300M25S02

0

1

2

3

4

40 50 60 70

rW, %

Stre

ngth

Los

s, M

Pa

300M15S05300M20S05300M25S05

(c) (d)

0

1

2

3

4

5

6

40 50 60 70

rW, %

Stre

ngth

Los

s, M

Pa

300M15S08300M20S08300M25S08

0

1

2

3

4

5

6

40 50 60 70

rW, %

Stre

ngth

Los

s, M

Pa

400M15S08400M20S08400M25S08

(e) (f)

Figure 5.8 Loss of Strength vs. W-B Ratio at 28 day Immersion in Sulfuric Acid


127

20

30

40

50

0 50 100 150 200


Stre

ngth

, MPa

300M15W45S05300M20W45S05300M25W45S05

10

20

30

40

50

0 50 100 150 200


Stre

ngth

, MPa

300M15W45S08300M20W45S08300M25W45S08

(a) (b)

20

30

40

50


Stre

ngth

, MPa

300M15W55S05300M20W55S05300M25W55S05

10

20

30

40

50


Stre

ngth

, MPa

300M15W55S08300M20W55S08300M25W55S08

(c) (d)

20

30

40

50

0 50 100 150 200


Stre

ngth

, MPa

300M15W65S05300M20W65S05300M25W65S05

10

20

30

40

0 50 100 150 200


Stre

ngth

, MPa

300M15W65S08300M20W65S08300M25W65S08

(e) (f)

Figure 5.9. Strength vs. Immersion Period in 5% and 8% Sulfuric Acid Solutions


128

0

1

2

3

4

5

6

0 2 4 6 8 10

Solution Strength, %

Stre

ngth

Los

s, M

Pa300M15W45300M15W55300M15W65

0

1

2

3

4

5

6

7

0 2 4 6 8 10


Stre

ngth

Los

s, M

Pa

400M15W45400M15W55400M15W65

(a) (b)

0

1

2

3

4

0 2 4 6 8 10


Stre

ngth

Los

s, M

Pa

300M20W45300M20W55300M20W65

0

1

2

3

4

5

6

0 2 4 6 8 10


Stre

ngth

Los

s, M

Pa400M20W45400M20W55400M20W65

(c) (d)

0

1

2

3

0 2 4 6 8 10


Stre

ngth

Los

s, M

Pa

300M25W45300M25W55300M25W65

0

1

2

3

4

5

0 2 4 6 8 10


Stre

ngth

Los

s, M

Pa

400M25W45400M25W55400M25W65

(e) (f)

Figure 5.10. Strength Loss vs. Solution Strength of Sulfuric Acid


129

30

40

50

0 10 20 30

rM, %

Stre

ngth

, MPa

300W45S02300W55S02300W65S02

30

40

50

0 10 20 30

rM, %

Stre

ngth

, MPa

300W45A02300W55A02300W65A02

(a) (b)

25

35

45

0 10 20 30

rM, %

Stre

ngth

, MPa

300W45S05300W55S05300W65S05

25

35

45

0 10 20 30

rM, %

Stre

ngth

, MPa

300W45A05300W55A05300W65A05

(c) (d)

25

35

45

0 10 20 30

rM, %

Stre

ngth

, MPa

300W45S08300W55S08300W65S08

25

35

45

0 10 20 30

rM, %

Stre

ngth

, MPa

300W45A08300W55A08300W65A08

(e) (f)

Figure 5.11. Comparison of action of Sulfuric and Acetic Acids


130

20

30

40

50

0 50 100 150 200


Stre

ngth

, MPa

400M20W45S05400M20W45A05

20

30

40

50

0 50 100 150 200


Stre

ngth

, MPa

300M20W45S05300M20W45A05

(a) (b)

30

40

50

60


Stre

ngth

, MPa

400M15W45S02

400M15W45A02

30

40

50

60


Stre

ngth

, MPa

300M15W45S02300M15W45A02

(c) (d)

15

25

35

45


Stre

ngth

, MPa

400M25W45S08400M25W55A08

20

30

40

50


Stre

ngth

, MPa

300M25W55S08300M25W55A08

(e) (f)

Figure 5.12. Strength vs. Immersion Period in Sulfuric & Acetic Acid Solutions


131

5.3 CALIBRATION AND VALIDATION OF THE MODEL

5.3.1 Mechanics of acid attack on concrete

According to Regourd (1981), acid attacks resulted in continuous and slow degradation of

engineering properties of concrete. It started with the degradation of the concrete surface

resulting in spalling of material from concrete. With the passage of time the degradation

process moved into the interior of concrete thus reducing the strength by increasing the

porosity and also increased content of coarse pores and amount of leaching of the

decomposed products.

As stated earlier, the two acids, a strong and a weak were used in this study. Sulfuric acid

was selected from the category of mineral acids while acetic acid was chosen from the

category of organic acids. Sulfuric acid is extremely harmful for concrete. It consumes the

hydration product and results in leaching of cement paste which further results in

weakening the interaction between aggregate and cement paste thus causing reduction in

strength of concrete.

In ordinary Portland cement during hydration process calcium hydroxide is produced as

given in eq. 5.8 & 5.9.

2 C3S + 6H C3S2H3 + 3CH (5.8)

2 C2S + 4H C3S2H3 + CH (5.9)

Metakaolin contains high percentage of reactive silica which reacts with CH released from

hydration of concrete to from C3S2H3 as given below.

3CH + 2S C3S2H3 (5.10)

Hence it makes concrete stronger. However in ordinary Portland cement the calcium

hydroxide thus produced is soluble in sulfuric acid and reacts to form gypsum.

H2SO4 + Ca(OH)2 CaSO4.2H2O(Gypsum) (5.11)

Gypsum is much weaker than C-S-H. The formation of calcium sulfate has the same

solubility as calcium hydroxide but the gypsum so produced attracts calcium aluminate

hydrates and forms ettringite as shown in eq. 5.11.

3CaSO4 .2H2O+ 3CaO.Al2O3.6H2O +19H2O 3CaO.Al2O3.3CaSO4.31H2O (5.12)

(Ettringite)


132

The Ettringite formation deteriorates concrete by amplification of wearing mechanism

within acidic solution. This mechanism also contributes to expansive destruction. Kim et.

al. (2007) studied durability properties of concrete using Korean metakaolin. The mortar

specimen containing variable dosage of metakaolin were subjected to 2% solution strength

of sulfuric acid along with the control paste made with OPC. The results showed significant

improvement in the resistance of metakaolin cement pastes in comparison to OPC paste.

Similar type of study was conducted by Girchi et. al. (2007). They compared the result of

OPC control mixtures with the mixtures containing natural pozzolans and lime filler

subjected to 3% solution strength of Sulfuric acid and 1% solution strength of Hydrochloric

acid. It was found that significant acid resistance was obtained when natural pozzolans and

lime filler were incorporated in cements.

Acetic acid belongs to the category of organic acids. It also deteriorates the concrete

surface but destruction level is weaker than that of sulfuric acid. It was reported by Lea

(1998) that higher concentration of organic acids leads to leaching of concrete. Acetic acid

reacts with free calcium hydroxide obtained from hydration of ordinary Portland cement as

shown in the following.

CH3COOH + Ca(OH)2 Ca(CH3COO)2 +2H2O (5.13)

Calcium acetate obtained in eq. 5.12 is a soluble material. It was reported by Bellew (1995)

that 10% solution of acetic acid is sufficiently strong to remove the cementitious

components of concrete and harmfully deteriorated concrete. The X-ray Diffraction

analysis of attacked ordinary Portland cement concrete was carried out and it was found

that white powder appearing on the concrete surface was calcium acetate.

3 CH + 2S C3S2H3 (5.14)

The addition of metakaolin which mainly consists of reactive silica, improves the hydration

process by eating up the calcium hydroxide as shown by eq. 5.13. Thus quantity of free

calcium hydroxide is reduced and this in turn reduces the gypsum and ettringite formation

which are both dangerous for concrete durability during sulfuric acid attack. In case of

Acetic acid as the quantity of free calcium hydroxide is decreased in comparison to

ordinary Portland cement; therefore the quantity of soluble calcium acetate is also reduced.


133

5.3.2 Calibration

As discussed in section 5.3.1 that the nature of attack for both the acids is different,

therefore, the strength loss data were broadly categorized into two different classes; Strong

Acid and Weak Acid, because the way strength was degraded due to acid attack was

different in each case of the two acids; see Figures 11 and 12 for example. It may be noted

that nature of variation in case of two acids is identical; however, the scale of variation is

different. It may be noted from Figure 12 (c, d) that 2% acetic acid solution does not

deteriorate strength, rather it adds to the strength as if the curing period is extended, where

as 2% sulfuric acid decreases the strength with increasing immersion period. All these

factors dictate for a separate calibration of same basic model in case of each of the two

acids.

In each of Rich and Normal classes 9 mixtures were cast each with two binder contents and

were immersed in 3 solution strengths; 2%, 5%, and 8%. The matured specimens with

standard moist curing of 28-day were tested to failure after 7, 28, 91 and 182 days of

immersion so the total number of strength data were 216 out of which half the data were

reserved for calibration of the model and the remaining half were kept for validation of the

model. The Tables 5.1 to 5.4 give the details of partition of data as well as the comparison

of experimental and predicted strengths.

The calibration was separately accomplished for normal and rich class concretes to find out

the coefficients aij, bij and cj. i.e., the coefficients 300 400 300 400 300 400, , , , ,ij ij ij ij j ja a b b c c were found

by separate calibration of the model from the data of 300 kg/m3 and 400 kg/m3 class

concretes for each acid. The two interpolation functions N as defined by Equation 5.6(d)

and (e) can used to interpolate for any given binder content between 300 kg/m3 and 400

kg/m3 of concrete.

As the action of weak and strong acids was altogether different, hence separate calibrations

were performed for each group of acids. Therefore two sets of models were finally

accomplished one each for Sulfuric acid and Acetic acid. The final coefficients of

regression have been incorporated in a computer model which is provided in Appendix A.


134

Table 5.1 Experimental and predicted strengths for binder content 300 kg/m3

Experimental Strength Predicted Strength Immersion Period 0 7 28 91 182 7 28 91 182 300M15W45S02 47.78 47.50 46.41 43.19 38.61 47.45 46.50 43.67 39.63 300M15W55S02 43.13 42.74 41.73 38.56 34.22 42.79 41.78 38.80 34.54 300M15W65S02 38.60 38.32 37.45 34.81 31.22 38.27 37.31 34.46 30.38 300M20W45S02 46.35 46.21 45.97 45.29 44.40 46.25 45.97 45.18 44.08 300M20W55S02 40.54 40.40 40.20 39.56 38.61 40.42 40.09 39.15 37.84 300M20W65S02 34.85 34.75 34.46 33.35 31.85 34.75 34.46 33.65 32.52 300M25W45S02 40.07 39.96 39.80 39.31 38.61 39.97 39.70 38.95 37.90 300M25W55S02 36.81 36.72 36.36 35.52 34.32 36.70 36.38 35.48 34.21 300M25W65S02 33.80 33.70 33.29 32.26 30.85 33.70 33.43 32.65 31.58





Note:- The shaded data has been used for calibration.


135









136


Experimental Strength Predicted Strength Immersion Period 0 7 28 91 182 7 28 91 182 300M15W45A02 47.78 48.02 48.72 50.98 54.54 48.03 48.77 51.02 54.29 300M15W55A02 43.13 43.30 43.57 44.89 46.65 43.26 43.68 44.93 46.75 300M15W65A02 38.60 38.69 38.81 39.31 40.00 38.66 38.84 39.40 40.22 300M20W45A02 46.35 46.65 47.61 50.84 55.50 46.66 47.61 50.47 54.61 300M20W55A02 40.54 40.64 41.34 43.30 46.33 40.74 41.36 43.21 45.90 300M20W65A02 34.85 35.05 35.34 36.36 37.64 34.98 35.36 36.52 38.22 300M25W45A02 40.07 40.58 41.73 45.56 51.20 40.52 41.88 46.00 51.95 300M25W55A02 36.81 37.21 38.19 41.34 46.24 37.15 38.18 41.29 45.80 300M25W65A02 33.80 33.99 34.81 37.58 41.51 34.06 34.87 37.29 40.80







137









138

5.3.3 Validation

As it has been stated earlier that the experimental data were divided into two halves; one

was used in calibration of the model and the other was employed for the validation of the

model. The predicted strength along with division of data has been given in Tables 5.1-

5.12. The quality of both calibration and validation is almost of the same nature and it may

be safely concluded that predictions agree with the experimental data excellently. For

comparison purpose the Figures 5.13 to 5.21 may be examined.


139

0

25

50

75

0 25 50 75

Experimental Strength, MPa

Pred

icte

d St

reng

th, M

Pa

Figure 5.13: Quality of Calibration for Concretes (300 kg/m3) Immersed in Sulfuric Acid

0

25

50

75

0 25 50 75


Pred

icte

d St

reng

th, M

Pa

Figure 5.14: Quality of Validation for Concretes (400 kg/m3) Immersed in Sulfuric Acid

+20%

-20%

+20%

-20%


140

0

25

50

75

0 25 50 75


Pred

icte

d St

reng

th, M

Pa

Figure 5.15: Overall Quality of Prediction for Concretes Immersed in Sulfuric Acid

0

25

50

75

0 25 50 75


Pred

icte

d St

reng

th, M

Pa

Figure 5.16: Quality of Calibration for Concretes (300 kg/m3) Immersed in Acetic Acid

+20%

-20%

+20%

-20%


141

0

25

50

75

0 25 50 75


Pred

icte

d St

reng

th, M

Pa

Figure 5.17: Quality of Validation for Concretes (400 kg/m3) Immersed in Acetic Acid

0

25

50

75

0 25 50 75


Pred

icte

d St

reng

th, M

Pa

Figure 5.18: Overall Quality of Prediction for Concretes Immersed in Acetic Acid

+20%

-20%

+20%

-20%


142

0

20

40

60

0 50 100 150 200

Immersion Period, days

Stre

ngth

, MPa

0

20

40

60

0 50 100 150 200


Stre

ngth

, MPa

a) Binder = 300 kg/m3, MK/B = 15% b) Binder = 400 kg/m3, MK/B = 15%

0

20

40

60

0 50 100 150 200


Stre

ngth

, MPa

0

20

40

60

0 50 100 150 200


Stre

ngth

, MPa

c) Binder = 300 kg/m3, MK/B = 20% d) Binder = 400 kg/m3, MK/B = 20%

0

20

40

60

0 50 100 150 200


Stre

ngth

, MPa

0

20

40

60

0 50 100 150 200


Stre

ngth

, MPa

e) Binder = 300 kg/m3, MK/B = 25% f) Binder = 400 kg/m3, MK/B = 25%

Figure 5.19 Experimental (filled circles) and model results (solid line) for metakaolin concrete exposed to 2% sulfuric acid.

(W/B = 0.45 Blue Color, 0.55-Red Color & 0.65-Green Color)


143

0

20

40

60

0 50 100 150 200


Stre

ngth

, MPa

0

20

40

60

0 50 100 150 200


Stre

ngth

, MPa


0

20

40

60

0 50 100 150 200


Stre

ngth

, MPa

0

20

40

60

0 50 100 150 200


Stre

ngth

, MPa


0

20

40

60

0 50 100 150 200


Stre

ngth

, MPa

0

20

40

60

0 50 100 150 200


Stre

ngth

, MPa





144

0

20

40

60

0 50 100 150 200


Stre

ngth

, MPa

0

20

40

60

0 50 100 150 200


Stre

ngth

, MPa


0

20

40

60

0 50 100 150 200


Stre

ngth

, MPa

0

20

40

60

0 50 100 150 200


Stre

ngth

, MPa


0

20

40

60

0 50 100 150 200


Stre

ngth

, MPa

0

20

40

60

0 50 100 150 200


Stre

ngth

, MPa





145

0

20

40

60

0 50 100 150 200


Stre

ngth

, MPa

0

20

40

60

80

0 50 100 150 200


Stre

ngth

, MPa


0

20

40

60

0 50 100 150 200


Stre

ngth

, MPa

0

20

40

60

0 50 100 150 200


Stre

ngth

, MPa


0

20

40

60

0 50 100 150 200


Stre

ngth

, MPa

0

20

40

60

0 50 100 150 200


Stre

ngth

, MPa


Figure 5.22 Experimental (filled circles) and model results (solid line) for metakaolin concrete exposed to2% acetic acid.



146

0

20

40

60

0 50 100 150 200


Stre

ngth

, MPa

0

20

40

60

0 50 100 150 200


Stre

ngth

, MPa


0

20

40

60

0 50 100 150 200


Stre

ngth

, MPa

0

20

40

60

0 50 100 150 200


Stre

ngth

, MPa


0

20

40

60

0 50 100 150 200


Stre

ngth

, MPa

0

20

40

60

0 50 100 150 200


Stre

ngth

, MPa


Figure 5.23 Experimental (filled circles) and model results (solid line) for metakaolin concrete exposed to 5% acetic acid.



147

0

20

40

60

0 50 100 150 200


Stre

ngth

, MPa

0

20

40

60

0 50 100 150 200


Stre

ngth

, MPa


0

20

40

60

0 50 100 150 200


Stre

ngth

, MPa

0

20

40

60

0 50 100 150 200


Stre

ngth

, MPa


0

20

40

60

0 50 100 150 200


Stre

ngth

, MPa

0

20

40

60

0 50 100 150 200


Stre

ngth

, MPa


Figure 5.24 Experimental (filled circles) and model results (solid line) for metakaolin concrete exposed to 8% sulfuric acid. (W/B = 0.45 Blue Color, 0.55-Red Color & 0.65-Green Color)


148

5.4 CARBONATION

Carbonation of concrete is a multi reactive phenomenon depending on many internal and

external factors. The external factors which affect the carbonation of concrete involve

relative humidity, ambient temperature and pressure while the internal factors include

concrete porosity, permeability, water-cement ratio, cement content, SCM-binder ratio,

hydration conditions, age and moisture content of concrete.

The above mentioned external and internal factors affect in a variety of ways during

carbonation because all the external and internal factors require controlled conditions in

order to quantify their role during carbonation process. However, in this study internal

conditions were kept same while external factors were beyond the control as the specimens

were subjected to open atmosphere after twenty eight days of curing. Although concrete

cubes were used for the determination of carbonation depth, therefore, they were placed in

such a way so that all sides shall be subjected to the open atmospheric conditions.

The main problems associated with carbonation involve the depassivation or corrosion of

steel in reinforced cement concrete which ultimately reduces the load carrying capacity of

the affected member. Bellow (1995) studied the effect of carbonation on corrosion of steel

inside concrete. He found that the steel present in reinforced cement concrete is protected

from corrosion due to high pH value of concrete which forms the passive layer of ferric

oxide around the steel. The carbonation process reduces the pH value of the solution which

ultimately results in corrosion of embedded steel.

5.4.1 Carbonation Process

The carbon dioxide, present in atmosphere, interacts with the concrete structures exposed to

atmosphere. The carbon dioxide gas penetrates into the concrete surface and interacts with

the water present in the pores of concrete to form carbonic acid which reacts with free CH

forming calcium carbonate as follows.

CO2 + H2O H2CO3 (5.15)

H2CO3 + Ca(OH)2 CaCO3 + H2O (5.16)

The reaction shown by the equations 5.15 and 5.16 bring the pH value in concrete below 9

or lower which is otherwise higher. The carbonic acid produced in equation 5.15 does not


149

react with concrete rather neutralizes the alkalinity in pore water. (Zivica et. al., 2001). The

above equations also highlight the importance of calcium hydroxide which plays a very

important role in the carbonation process. According to Broomfield (1997), hydration

products of concrete other than calcium hydroxide may also be decomposed. These

products after decomposition may result into calcium carbonate and hydrated silica,

alumina and ferric oxide at the time of full carbonation of concrete.

Although carbonation is a complex phenomenon however, the major contributing factors

during carbonation of concrete are discussed as follows.

Permeability of concrete is very important during carbonation of concrete. Permeability is

directly linked with the pore structure of concrete. CO2 can only diffuse in air filled pores

of concrete, the presence of water inside the pores of concrete blocks the passage of CO2

into concrete but it also produces a favorable condition of reaction between carbon dioxide,

water and calcium hydroxide to form calcium carbonate. Therefore there shall be some

critical value of relative humidity at which the process of carbonation is aggressive. Zivica

et al. (2001) have found that carbonation process increases when relative humidity is within

the range of 50-75% but decreases for relative humidity range of 0-45% and 75-100%.

They also found that external factor of relative humidity is also dependent on many internal

factors such as porosity or permeability of concrete. The permeability of a concrete mixture

increases when water-cement or water-binder ratio exceeds 0.6. They linked the rise in

permeability of concrete matrix with increase in capillary pores when water-binder ratio is

exceeding 0.6.

Carbonation depth in concrete structures is also dependant on the cement content of

concrete. Increase in cement content increases the binding capacity of the concrete matrix

which means smaller number of pores in concrete matrix. Zivica et al. (2001) also studied

the effect of cement content in carbonation. According to the authors, increase in cement

content decreases the permeability; provided that, the water-binder ratio is less than 0.6

which ultimately reduces the carbonation. They also concluded that concrete with cement

content 300 Kg/m3 or greater gives the reasonable protection against the carbonation if

properly cured.

The above discussion concludes with a fact that carbonation is dependent on many factors.

The permeability or porosity of concrete is very prominent among the internal factors.


150

Concrete with less permeability would show good resistance against carbonation. The use

of supplementary cementing material such as metakaolin (more finer than cement)

increases the packing of concrete thus reducing the permeability of concrete. On the other

hand metakaolin contains silica which eats up the free CH during the hydration of cement

which further slows down the carbonation process in comparison to ordinary Portland

cement concrete.

5.5 DISCUSSION ON CARBONATION RESULTS

This study contains two different types of cement content i.e. 300 and 400 kg/m3. The

water-binder ratios used were 0.45, 0.55 and 0.65. Metakaolin-binder ratios used were 0,

15, 20 and 25%. Concrete cubes were cured for twenty eight days before placing them into

the open atmosphere. The carbonation depth was determined by halving the concrete cubes

into two and then running the phenolphthalein indicator as discussed in chapter-4.

Carbonation depths were determined at 4, 7, 13, 25 and 52 week time interval. The

carbonation depth for two cement content is discussed in the following section.

5.5.1 Discussion on Carbonation depth for cement content 300 kg/m3

Figure 5.25 shows the carbonation depth in concrete cubes with 300 kg/m3 cement content.

The variety in water-binder ratios and metakaolin-binder ratios are also plotted on the same

axis for comparison purpose. Average relative humidity of Lahore during last year was

37.9%. Since all the specimens were subjected to same relative humidity; therefore, in this

study it is a prime factor but not the unique contributor for carbonation depth. The increase

in permeability is reflected from water-binder ratios. Metakaolin-binder ratio for a typical

water-cement ratio indicates the reduction in permeability of the concrete matrix. The

carbonation depth for the various mixtures in figure 5.25 follows the similar pattern as

being observed by other researchers. The carbonation depth decreases with the reduction in

water-binder ratio and increases with the increase of water-binder ratio i.e. due to increase

of permeability. The results are distinctive from 400 Kg/m3 cement content when compared

for fixed water-binder ratio and varying metakaolin-binder ratio. The carbonation depth for

15% of metakaolin-binder ratio was found to be more than that of 20% and 25%

replacement levels. The carbonation depth becomes almost similar for 20% and 25% of

metakaolin-binder ratios. Therefore, it can be suggested that 20% replacement level shall

be considered for cement content 300 Kg/m3.


151

0

2

4

6

8

10

12

300M

00W

45

300M

15W

45

300M

20W

45

300M

25W

45

300M

00W

55

300M

15W

55

300M

20W

55

300M

25W

55

300M

00W

65

300M

15W

65

300M

20W

65

300M

25W

65

Sample Designation

Carb

onat

ion

dept

h(m

m)



There is clear distinction between carbonation depth for ordinary Portland cement concrete

and metakaolin concrete. The primary reason of reduction of carbonation depth in

metakaolin concrete is the dense packing of concrete matrix which ultimately reduces the

carbonation. The other important factor is the chemical phenomenon shown by equation

5.16. The metakaolin present in concrete eats up the free CH which is a soluble material as

shown by eq. 5.10 Therefore, lesser quantity of CH slows down the carbonation process

and hence resulting in smaller carbonation depths.

5.5.2 Discussion on Carbonation depth for cement content 400 kg/m3

Figure 5.26 presents the carbonation depth for binder content 400 kg/m3 for variable water-

binder and metakaolin-binder ratio. The increase in cement content improves the binding of

concrete matrix. The carbonation depth pattern obtained for this binder content is similar to

the carbonation depth obtained for 300kg/m3 binder content but magnitude of carbonation

depth was found to be reduced for increased cement content. Figure 5.26 clearly indicates

that presence of metakaolin reduces the carbonation depths, however, comparison of

carbonation depths for fixed water-binder ratios, it was found that 15% of metakaolin-

binder ratio is sufficient for carbonation resistance of concrete. There is absolutely no doubt

that reduction in carbonation depth was resulting from reduction in permeability of matrix.

The decrease in carbonation depth for concrete mixtures with varying metakaolin

replacement level is mainly due to dense packing of concrete matrix and reduced level of

CH obtained during the hydration of concrete.


152

0

1

2

3

4

5

6

7

400M

00W

45

400M

15W

45

400M

20W

45

400M

25W

45

400M

00W

55

400M

15W

55

400M

20W

55

400M

25W

55

400M

00W

65

400M

15W

65

400M

20W

65

400M

25W

65

Sample Designation

Carb

onat

ion

dept

h(m

m)



The above discussion on results clearly relates the carbonation depth with relative humidity

and permeability of concrete. The permeability of concrete is dependent on many factors

like compaction, cement content, water-binder ratio, metakaolin-binder ratio, curing age

and curing conditions. It was also noticed that chemical composition of metakaolin also

plays a very important role in carbonation. Kim et. al. (2007) studied the properties of high

strength concrete using Korean metakaolin. He found increased carbonation depths for

concrete mixtures having varying proportions of metakaolin. This behavior of metakaolin

mixture was observed due to the presence of high percentage of ferric oxide (2.5%) present

inside the Korean metakaolin. The Pakistani metakaolin contains only 0.24% of Ferric

oxide. The chemical composition of other compounds was found to be identical for both

the metakaolins. The other researchers found the positive role of metakaolin in resisting

carbonation attack on concrete. This shows that the process of carbonation may be affected

with the chemical composition of supplementary cementing material especially ferric oxide

as it is directly linked with the corrosion of steel.

Figures 5.25 and 5.26 can be used very effectively as a ready reference for carbonation

depths. The known cement content, water-binder ratio and metakaolin-binder ratio of any

concrete mixture can be used to estimate its carbonation depth for one year provided the


153

relative humidity is within the limit which is cited above. The carbonation depth for any

metakaolin-binder ratio of Pakistani metakaolin will always be smaller than ordinary

Portland cement concrete.

5.6 SUMMARY

This chapter discusses the chemical reaction of metakaolin and cement in presence of

water. It discusses the role of metakaolin in resisting the acid attack on concrete. The

strength of concrete was degraded due to immersion in acid solution of variable

concentrates. A strength degradation model was proposed using statistical approach. The

model was based on physical parameters like binder content, metakaolin-binder ratio,

water-binder ratio, solution strength of acid and immersion period. One half of the

experimental data was used in the calibration of the model and the other half was used for

validation of the model. The model prediction agrees quite closely with the experimental

data. The last section of the chapter presents reference chart for carbonation of metakaolin

concrete in comparison to the ordinary Portland cement concrete.

CHAPTER-6

154

CONCLUSIONS AND RECOMMENDATIONS

6.1 CONCLUSIONS Following conclusions have been drawn from the results of this study.

1. Kaolin clay obtained from Nagar Parkar deposits is fit for the production of

metakaolin.

2. This clay can be converted into highly reactive metakaolin by calcining at 800°C

for 8 hours.

3. The compressive strength of concrete is related both with metakaolin-binder ratio

and water-binder ratio. The maximum strength is obtained at 15% replacement

level for all water-binder ratios.

4. It has been found that acid resistance of metakaolin concrete is much better than

ordinary Portland cement concrete. The rich content of silica from metakaolin

reduces free calcium hydroxide during hydration of concrete which ultimately

improves the acid resistance of metakaolin concrete.

5. The study has shown that there are five variables which are affecting the acid

resistance of metakaolin concrete i.e. binder content “B”, metakaolin to binder

ratio “rM” , water to binder ratio “rW”, solution strength of acid “S” and immersion

period in acid “t”.

6. For all water-binder ratios studied the metakaolin-binder ratio of 20% showed the

best resistance to carbonation for concrete made with binder content of 300 kg/m3

and the metakaolin binder ratio of 15% gave the maximum resistance to

carbonation for concretes prepared with binder content 400 kg/m3.

CHAPTER-6 CONCLUSIONS AND RECOMMENDATIONS

155

6.2 RECOMMENDATIONS FOR FUTURE STUDY The following recommendations for future study are made based upon the

research conducted in this study.

1. Kaolin clay deposits available in Swat district of Khyber Pakhtunkhawa province

may be explored for the production of metakaolin.

2. Gradual calcination has been used in this study for the production of metakaolin.

The reactivity of metakaolin may be studied using flash calcination.

3. The acid resistance of metakaolin concrete may be explored for the flowing

conditions.

4. Carbonation charts are prepared according to the metrological conditions of

Lahore over the whole year. The carbonation depths may be studied for fixed

humidity and pressure.

5. The acid resistance of metakaolin concrete may be studied for different type of

cements other than Ordinary Portland Cement.

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APPENDIX A

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APPENDIX

Program

implicit real*8 (A-H,O-Z) Dimension Weak3(6,3),Strong3(6,3),Weak4(6,3),Strong4(6,3) Dimension a(6,3),S(3),rM(3),rW(2),Alpha(6), Age(4),FC(4) CHARACTER*1 TYPESS CHARACTER*6 AAAA CHARACTER XXXX Age(1)=7. Age(2)=28. Age(3)=91. Age(4)=182. open(1,File="Coeff.Txt") Read(1,*) AAAA do 11 i=1,6 11 Read(1,*) Strong3(i,1),Strong3(i,2),Strong3(i,3) C write(*,*)Strong3(i,1),Strong3(i,2),Strong3(i,3) do 12 i=1,6 12 Read(1,*) Strong4(i,1),Strong4(i,2),Strong4(i,3) C Write(*,*) Strong4(i,1),Strong4(i,2),Strong4(i,3) READ(1,*) AAAA do 21 i=1,6 21 Read(1,*) Weak3(i,1),Weak3(i,2),Weak3(i,3) C write(*,*) Weak3(i,1),Weak3(i,2),Weak3(i,3) do 22 i=1,6 22 read(1,*) Weak4(i,1),Weak4(i,2),Weak4(i,3) C write(*,*) Weak4(i,1),Weak4(i,2),Weak4(i,3) write(*,*) "Interactive Mode or File Mode?" write(*,*) "Enter I for interactice Mode or Give Data File Name" write(*,*) "for File Mode" write(*,*) read(*,*) XXXX if(XXXX.eq."I". or. XXXX.EQ."i") Then ISWITCH=1 goto 200 else ISWITCH=0 goto 300 end if 200 write(*,*) write(*,*) "Provide 28day Cylinder Strength, Binder Content," write(*,*) "M/B,W/B,Solution Strength, Acid Type S or A" read(*,*) fc28 if (fc28.eq.0) then stop else read(*,*) B,rMM,RWW,SS,TYPESS

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endif goto 400 300 open(2,File=XXXX) Read(2,*) XXXX open(3,File=XXXX) read(2,*) NCases NNN=NCases 350 read(2,*) fc28,B,rMM,RWW,SS,TYPESS NNN=NNN-1 400 CALL MAKES(SS,S) if(TYPESS.eq."S") then CALL GetA(Strong3,Strong4,B, A) else CALL GetA(Weak3,Weak4,B, A) endif CALL MAKErM(rMM,rM) CALL MAKErW(rWW,rW) CALL GetALPHA(A,S,Alpha) DelFcR=0. do 477 i=1,3 write(*,*) Alpha(i) 477 DelFcR=DelFcR+Alpha(i)*rM(i) do 478 i=4,5 write(*,*) Alpha(i) 478 DelFcR=DelFcR+Alpha(i)*rW(i-3) write(*,*) Alpha(6) do 500 kk=1,4 T=Age(kk) FC(kk)=fc28+(DelFcR+Alpha(6)*dLog10(T))*T 500 write(*,*) Age(kk),DelFcR+Alpha(6)*dLog10(T) If (ISWITCH.eq.1) then write(*,*) FC(1),FC(2),FC(3),FC(4) goto 200 else write(3,*) B,rMM,RWW,SS,TYPESS,fc28,FC(1),FC(2),FC(3),FC(4) if (NNN > 0) then goto 350 end if end if stop END Subroutine GetA(S3,S4,BC,A) implicit real*8 (A-H,O-Z) dimension S3(6,3),S4(6,3),A(6,3) BB=BC-300. Shap300=1.-BB/100. Shap400=BB/100

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do 33 i=1,6 do 33 j=1,3 A(i,j)=S3(i,j)*Shap300+S4(i,j)*Shap400 33 Continue return end Subroutine MakeS(SS,S) implicit real*8 (A-H,O-Z) Dimension S(3) S(1)=1 S(2)=SS S(3)=SS*SS return end Subroutine MAKErM(aa,a) implicit real*8 (A-H,O-Z) Dimension a(3) a(1)=aa a(2)=aa*aa a(3)=a(1)*a(2) return end Subroutine MAKErW(aa,a) implicit real*8 (A-H,O-Z) Dimension a(2) a(1)=aa a(2)=aa*aa return end subroutine GetALPHA(A,S,Alpha) implicit real*8 (A-H,O-Z) Dimension A(6,3),S(3),Alpha(6) do 33 i=1,6 Alpha(i)=0.0 do 33 j=1,3 33 Alpha(i)=Alpha(i)+A(i,j)*S(j) return end

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File “Coeff.Txt” STRONG -1.35208815975850,-0.06925529808568,0.03314396168885 26.79696555717160,-6.90834143112632,0.56293995501181 -75.6650668855128,24.09751416609890,-2.12354974292354 -0.550133668751829, 0.231146267809995,-0.039198050044877 0.477945967552543,-0.196531810635535,0.033998163424669 0.006559737452719,-0.003826516997157,0.000595518640365 0.84116085735060,-0.25206970670734,0.12009460305611 -6.01524630804121,3.55434704683103,-0.79056797704812 12.80088053691550,-9.02760793016820,1.59044240122798 -0.186621604561224,-0.127978185625086,-0.023055597559154 0.154792828523224,0.142776277601904,0.019114661338652 0.010869383645629,-0.005739042745715,0.000856800992847 WEAK 3.483664732683330,-0.435585133116667,0.0 -16.0814435555556,0.56877988888889,0.239073444444444 24.6571666666666,2.77046533333334,-0.860429333333334 -0.340221777777778,-0.045668055555556,0.006339222222222 0.11122031111111,0.087542455555556,-0.009760255555556 -0.005729151611111,0.003903188594444,-0.000410277494444 5.09582733333333,-2.00249433333333,0.142548333333333 -2.72003199999998,0.346044366666668,0.264947766666667 -29.7712044444445,15.0842189444445,-1.98926261111112 -1.98053766666667,0.832022633333333,-0.0770019 1.60039017777778,-0.726256327777778,0.069330494444445 -0.000764195444444,0.002480217944444,-0.000324297611111

DEVELOPMENT OF STRENGTH AND DURABILITY OF CONCRETE...

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