CHAPTER 3 COMPOSITION OF MATERIALS FOR SELF COMPACTING...

Composition of materials for self compacting concrete

Effect of curing techniques on mechanical properties of self compacting concrete 77

CHAPTER 3 COMPOSITION OF MATERIALS FOR

SELF COMPACTING CONCRETE 3.1 Introduction

This chapter discusses the selection and testing of constituent materials for self

compacting concrete (SCC) and normal vibrated concrete (NVC), describes the

preparation and emphasizes their usefulness. It covers different curing techniques

used in this research and development of self curing self compacting concrete

(SCSCC) and its mechanism.

Ordinary portland cement, fly ash, aggregates (Gravel, Grit & Sand), normal tap

water, polycarboxylate-based superplasticizers, membrane forming curing

compound and self curing compound polyethylene glycols were selected to produce

various self-compacting concrete and its curing. The component materials were

tested to examine their suitability and to obtain several physical properties required

for the mixture proportioning process of concrete. The materials were procured in

sufficient quantity at the beginning of experimental work, in order to ensure

uniformity of results in terms of avoiding variation in results in entire investigation.

Following sections describe the constituent materials along with the experiments

conducted.

Self-compacting concrete (SCC) is a fluid mixture, which is suitable for placing in

difficult conditions and in structures with congested reinforcement, without

vibration [Khayat 1996][76]. In principle, a self-compacting or self-consolidating

concrete must:

* Have a fluidity that allows self-compaction without external energy,

* Remain homogeneous in a form during and after the placing process, and

* Flow easily through reinforcement Generally, SCC has to have a proper flowability and viscosity, so that the coarse

aggregate can float in the mortar without segregating. To achieve a balance between

flowability and stability, the total content of particles finer than the 150 ppm has to

be high, usually about 520 to 560 kg/m3 [Nagamoto and Ozawa 1999][106].

Self-compacting concretes are divided into three different types according to the

composition of the mortar: Powder type, Viscosity-modifying agent (stabilizer) type

& Combination type.

For the powder type, a high proportion of fines produce the necessary mortar

volume, whilst in the stabilizer type, the fines content can be in the range admissible



for vibrated concrete. The viscosity required to inhibit segregation will then be

adjusted by using a stabilizer [Nagamoto and Ozawa 1999][106]. The combination

type is created by adding a small amount of stabilizer to the powder type to balance

the moisture fluctuations in the manufacturing process.

However, after completion of proper proportioning, mixing, placing, curing, and

consolidation, hardened concrete becomes a strong, durable, and practically

impermeable building material that requires no maintenance.

3.2 MATERIALS USED IN SCC

3.2.1 Cement

In the most general sense of the word, cement is a binder, a substance that sets and

hardens independently, and can bind other materials together. The most important

use of cement is the production of mortar and concrete for bonding of natural or

artificial aggregates to form a strong building material that is durable in the face of

normal environmental effects. Concrete is a combination of cement, aggregate and

water.

Cement is a powder manufactured from limestone that is mixed with other

aggregates, notably sands, gravels and stone, to produce mortars and concretes.

High-quality cements require raw materials of adequate purity and uniform

composition. The vast majority of cement used in the India is portland cement,

sometimes referred to as Ordinary Portland Cement or OPC; although there are also

specialist cements, such as Sulphate-Resistant Cement (SRC) and High-Alumina

Cement (HAC) which are often used for sub-surface works. Indian standards

IS:12269- [2013][69] outlines the specifications for OPC 53 grade cement.

3.2.1.1 Ordinary Portland Cement (OPC)

Portland cement is the most common type of cement in general usage. It is a basic

ingredient of concrete, mortar and plaster. It consists of a mixture of oxides of

calcium, silicon and aluminum. Portland cement and similar materials are made by

heating limestone (a source of calcium) with clay and grinding this product (called

clinker) with a source of sulfate (most commonly gypsum).



Ordinary Portland Cement of 53 grade conforming to IS:12269- [2013][69] is used for

studies.

When Portland cement is mixed with water, its constituent compounds undergo a

series of chemical reactions that are responsible for the eventual hardening of

concrete. Reactions with water are designated hydration, and the new solids formed

on hydration are collectively referred to as hydration products. During hydration

dicalcium silicate (C2S) and tricalcium silicates (C3S) chemically react with water and

calcium silicate hydrates (C-S-H) are produced. The calcium silicates provide most of

the strength developed by Portland cement. C3S provides most of the early strength

(in the first three to four weeks) and both C3S and C2S contribute equally to ultimate

strength [Neville 2008][115].

3.2.1.2 Physical properties of OPC

The physical properties of cement significantly influence the performance of

concrete. This is also true for SCC. The cement used for SCC should have sound flow

and setting properties. It should enhance the fluidity of concrete and should be free

from false setting due to premature stiffening within a few minutes of mixing with

water. Also, it should be compatible with the chemical admixtures such as

superplasticizers, VMA, curing compounds and polyethylene glycols.

Lump-free fresh cement should be used in SCC. The cement should possess carefully

controlled fineness, and should produce low or moderate heat of hydration to

control the volume changes in concrete. IS:12269- [2013][69] and ASTM-C-150

[2007][15] have specified the specifications for ordinary portland cements, which are

also useful to choose the proper cement for SCC.

Table 3.1 below shows the physical properties of cement for the studies. In addition,

the relative density of cement was 3.15. The density of portland cement usually

varies from 3.10 to 3.25. Thus, the cement was physically suitable to produce the

concretes for this study.



Table 3.1: Physical Properties of Portland cement

PROPERTY VALUE IS CODE IS :

12269-2013

Consistency 28% 30-35

Fineness m2/kg 257 225

Initial setting time 35min 30min minimum

Final setting time 178min 600min maximum

Compressive strength at 7

days N/mm2

38.49 N/mm2 37 N/mm

2

Compressive strength at 28

days N/mm2

52.31 N/mm2 53 N/mm

2

3.2.1.3 Chemical composition of OPC

The chemical analysis of portland cement has revealed that it mostly consists of

various oxide compounds. The major oxide compounds are lime, silica, alumina, and

iron. In addition, two minor oxides namely sodium and potassium oxides are of some

importance, particularly with regard to alkali-aggregate reactions in concrete. In

addition, magnesia and sulfuric anhydrite can be present, although they are not

beneficial constituents of cement.

The chemical composition of the OPC used for studies is shown in Table 3.2.

Table 3.2: Chemical composition of OPC – 53 grade

Name & Composition Mass content (%)

Calcium oxide (lime) 61.3

Silicon dioxide (silica) 20.1

Aluminum oxide (alumina) 4.51

Ferrous and ferric oxides (iron oxides) 0.51

Magnesium oxide (magnesia) 1.0

Sulfur trioxide (sulfuric anhydrite) 3.0

Alkaline oxides (alkalis) 1.1

C2S, C3S, C3A, C4AF 24-26, 48-52, 7-8, 11-20%

3.2.2 Fly Ash as SCM:

The Fly Ash story begins 2000 years ago...When the Romans built the Colosseum in

the year 100 A.D. - that still stands the test of time!! The ash generated from

Volcanoes was used extensively in the construction of Roman structures. Colosseum

is a classic example of durability achieved by using volcanic ash. The building

constructed 2000 years ago and still standing today! Only difference is, Fly Ash is



generated in artificial volcanoes - coal fired kilns. It is a byproduct or an industrial

waste.

Fly ash is one of the most extensively used by-product materials in the construction

field resembling Portland cement. It is an inorganic, noncombustible, finely divided

residue collected or precipitated from the exhaust gases of any industrial furnace.

Most of the fly ash particles are solid spheres and some particles, called

cenospheres, are hollow (Fig. 3.1) [Kosmatka et al. 2002][85]. Also present are

plerospheres, which are spheres containing smaller spheres inside. The particle sizes

in fly ash vary from less than 1 ppm to more than 100 ppm with the typical particle

size measuring under 20 ppm. Their surface area is typically 300 to 500 m2/kg. Fly

ash is primarily silicate glass containing silica, alumina, iron, and calcium. The relative

density or specific gravity of fly ash generally ranges between 1.9 and 2.8 and the

color is generally gray or tan. [Druta 2003][35, Kasemchaisiri and Tangtermsirikul

2008][75].

Fig. 3.1: SEM micrograph of fly ash particles [Kosmatka et al. 2002][85]

3.2.2.1 Role of Fly Ash in concrete

Although their usage is mainly economic (fly ash is much cheaper than cement), the

addition of fly ash has many technical benefits. Dosage of fly ash varies with the

reactivity of the ash and the desired effects on the concrete [Mindess et al.

2003][104]. Many class C ashes when exposed to water will hydrate and harden in less

than 45 minutes. In concretes, class F fly ash is often used at dosages of 15% to 25%



by mass of cementitious material and class C fly ash is used at dosages of 15% to

40%.

Fly ash has a high amount of silica and alumina in a reactive form. These reactive

elements complement hydration chemistry of cement. When cement reacts with

water, due to hydration, cement produces C-S-H gel. This C-S-H gel binds the

aggregates together and strengthens our concrete. One more compound Calcium

Hydroxide Ca(OH)2 is produced on hydration known as Free Lime. Aggressive

environmental agents like water, sulphates & CO2 attack this free lime leading to

deterioration of the concrete. The cement technologists observed that the reactive

elements present in fly ash convert the problematic free lime into the beneficial C-H-

S Gel.

Ca(OH)2 + SiO2 => C-S-H Gel

Ca(OH)2 + Al2O3 = C-Al-H Gel

It is not only the chemistry provided by fly ash that compliments chemistry of

cement, but also the physical properties of fly ash improve the rheology and

microstructure of concrete by a great extent. Fly ash, on itself, cannot react with

water; it needs free lime, produced on hydration of cement to trigger off its

pozzolonic effect. Once it is triggered, it can go on and on. Thus fly ash improves long

term strength of concrete due to the continued pozzolonic reaction. Fly ash makes

concrete denser, and hence less permeable, mainly by reducing water demand in

concrete and improving microstructure of concrete.

3.2.2.2 Properties of fly ash used for reference mix

The fly ash used for this study was given for testing to Sophisticated Instrumentation

Centre for Applied Research and Testing (SICART). The fly ash used in this study has

physical color Grey with specific gravity 2.13. The physical and chemical composition

of the fly ash used for studies along with the acceptable criteria as per [IS:3812-Part-I

2003][62, IS:3812-Part-II 2003][63] is shown in Table 3.3.



Table 3.3: Properties & Chemical constituents of fly ash used

Constituents’ property % by mass for Fly

Ash used

Requirement as per IS:

3812-2003

Source Vanakbori thermal power plant, Gujarat, India

Class & Color Class “F”, Grey

Specific gravity 2.13

Fineness, specific surface area 338 m2/kg >320

Loss on ignition 1.03 5% Max.

Silica (SiO2) 63.98 35 % Min. by mass

Iron Oxide (Fe2O3) 3.44 Silica+Al2O3+ Fe2O3 >

70% Alumina (Al2O3) 28.20

Calcium Oxide (CaO) 2.23

Magnesium Oxide (MgO) 1.45 5.0 % Max.

Total Sulphur trioxide (SO3) 0.165 3.0 % Max.

Alkalies:

Sodium Oxide (Na2O)

Potassium Oxide (K2O)

0.28

0.26

1.5 % Max. by mass

3.2.3 Aggregates

Generally, aggregates occupy 70% to 80% of the volume of concrete and have an

important influence on its properties. They are granular materials, derived for the

most part from natural rock (crushed stone, or natural gravels) and sands, although

synthetic materials such as slags and expanded clay or shale are used to some

extent, mostly in lightweight concretes [Mindess et al. 2003][104]. In addition to their

use as economical filler, aggregates generally provide concrete with better

dimensional stability and wear resistance. Although aggregate strength can play

sometimes an important role, for example in high-strength concretes, for most

applications the strength of concrete and mix design are essentially independent of

the composition of aggregates. However, in other instances, a certain kind of rock

may be required to attain certain concrete properties, e.g., high density or low

coefficient of thermal expansion [Neville 2008][115].

In order to obtain a good concrete quality, aggregates should be hard and strong,

free of undesirable impurities, and chemically stable. Aggregates should also be free

of impurities like silt, clay, dirt, or organic matter. Due to these coatings on the

aggregates, they will isolate the aggregate particles from the surrounding concrete,



causing a reduction in strength. Silt, clay and other fine materials will increase the

water requirements of the concrete, and the organic matter may interfere with the

cement hydration. [Neville 2008][115]

3.2.3.1 Types of Aggregates — Aggregates for concrete are divided into two types as

follows (Fig. 3.2):

Fig. 3.2: Types of aggregates

3.2.3.2 Fine Aggregates (Sand)

Sand is a naturally occurring granular material composed of finely divided

rock and mineral particles. The composition of sand is highly variable, depending on

the local rock sources and conditions, but the most common constituent of

sand is silica (silicon dioxide, or SiO2), usually in the form of quartz.

Locally available sand in the form of natural pit sand by source was used as the fine

aggregate (FA). The sand was found as deposits in soil, and obtained by forming pits

into the soil. The sand was tested for mass passing 4.75 mm sieve. Moreover, the

sieve analysis and other tests were performed for the sand in accordance with

IS:383- [1970][57] and IS:2386- [1963][61].

3.2.3.3 Properties of sand

The test results for the physical properties of are presented in Table 3.4. The

properties of sand indicated that it was suitable for use to produce the concretes.

The bulk density, fineness modulus and specific gravity were within permissible

Aggregate

Fine Sand

< 4.75mm

Course

Grit

4.75mm to 12.5mm

Gravel

> 12.5mm

http://en.wikipedia.org/wiki/Rock_(geology)

http://en.wikipedia.org/wiki/Mineral

http://en.wikipedia.org/wiki/Silica

http://en.wikipedia.org/wiki/Quartz



limits specified by the Indian standards IS:2386- [1963][61].

The bulk density of sand was 1776 kg/m3, which is greater than that of aggregates.

The bulk density of sand is generally higher than that of coarse aggregate due to

reduced void content. However it is favorable that the difference in densities is not

much as large difference between the relative densities of fine and coarse

aggregates leads to increased segregation in concrete. The absorption of sand

obtained was 1.23%. The absorption of fine aggregate generally varies in the range

of 0.2 to 3.0% [Neville 2008][115]. Hence, the absorption of concrete sand was in the

lower range, which is beneficial for concrete properties and durability. The total

evaporable moisture content of sand was 0.1%, which is the same as that of

aggregates. The reason may be the identical drying condition.

Table 3.4: Properties of Sand or fine aggregates

Property Value of Sand

Source Bodeli, Gujarat

Color Yellowish White

Zone Zone II

Specific Gravity 2.55

Fineness Modulus 2.87

Bulk Density 1776 kg/m3

Water Absorption 1.73%

Surface moisture 0.1%

3.2.3.4 Coarse aggregates

As a basic raw material aggregates can be put to many uses, although certain tasks

may require a specific type of aggregate.

Aggregates are the most mined material in the world. Aggregates are a component

of composite materials such as concrete and asphalt concrete; the aggregate serves

as reinforcement to add strength to the overall composite material. Due to the

relatively high hydraulic conductivity value as compared to most soils, aggregates are

widely used in drainage applications such as foundation and French drains, septic

drain fields, retaining wall drains, and road side edge drains.

Aggregates are also used as base material under foundations, roads, and railroads. In

other words, aggregates are used as a stable foundation or road/rail base with

predictable, uniform properties (e.g. to help prevent differential settling under the



road or building), or as a low-cost extender that binds with more expensive cement

or asphalt to form concrete.

3.2.3.5 Coarse aggregate (Grit)

Grit is granular material which can be between coarse sand and pebbles. Generally

4.75mm-12.5mm in size, grit has limited uses in the construction industry on its own,

other than as a surface dressing. However, over recent years with the development

in block paving specifications, it has become a viable alternative bedding material for

permeable paving and other forms of elemental paving used in areas of high water

ingress. A small portion of these aggregates used in SCC increases the flowability and

segregation resistance.

3.2.3.6 Properties of coarse aggregates (Grit)

The test results for the properties of grit are presented in Table 3.5. The properties

of grit indicated that it was suitable for use to produce the concretes. The bulk

density, fineness modulus and specific gravity were within permissible limits

specified by the Indian standards IS:2386- [1963][61].

The bulk density of grit was 1764 kg/m3, which is lesser than that of sand. The bulk

density of aggregates generally varies from 1200 to 1780 kg/m3 [Kosmatka et al.

2002][85]. It includes the pores and voids existing in aggregates.

The bulk density of aggregates is generally lower than that of sand due to increased

void content. However it is favorable that the difference in densities is not much as

large difference between the relative densities of fine and coarse aggregates leads to

increased segregation in concrete. The absorption of grit obtained was 1.58%. The

absorption of fine aggregate generally varies in the range of 0.5 to 4.5% [Neville

2008][115]. Thus, the absorption of grit was in the lower range, which is good for

concretes. A higher absorption value is indicative of greater pores in aggregates that

might affect the strength and durability of concretes.

Table 3.5: Properties of Coarse Aggregate-Grit

Property Value of Grit

Source Sevalia, Gujarat

Colour Grayish Black




Absorption 1.48%




3.2.3.7 Coarse aggregate (Gravel)

Granular material which can be of almost any rock types, It is usually between 60mm

and 4.75 mm in size which may be rounded, if from a marine or fluvial source, or

angular if a quarried and crushed product. Gravels are sold in mixed sizes, e.g. 20-

5mm or closely graded to a specific size, such as 10mm.

The advent of modern blasting methods enabled the development of quarries, which

are now used throughout the world, wherever competent bedrock deposits of

aggregate quality exist. In many places, good limestone, granite, marble or other

quality stone bedrock deposits do not exist. In these areas, natural sand and gravel

are mined for use as aggregate. Where neither stone, nor sand and gravel, are

available, construction demand is usually satisfied by shipping in aggregate by

rail, barge or truck. Additionally, demand for aggregates can be partially satisfied

through the use of slag and recycled concrete. However, the available tonnages and

lesser quality of these materials prevent them from being a viable replacement for

mined aggregates on a large scale.

3.2.3.8 Properties of coarse aggregates (Gravel)

The test results for the properties of coarse aggregates-gravel are presented in Table

3.6. The properties of gravel indicated that it was suitable for use to produce the

concretes. The bulk density, fineness modulus and specific gravity were within

permissible limits specified by the Indian standards IS:2386- [1963][61].

The bulk density of gravel was 1725 kg/m3, which is lesser than that of sand. The

bulk density of aggregates generally varies from 1200 to 1750 kg/m3 [Kosmatka et al.

2002][85]. It includes the pores and voids existing in aggregates. The bulk density of

aggregates is generally lower than that of sand due to increased void content.

However it is favorable that the difference in densities is not much as large

difference between the relative densities of fine and coarse aggregates leads to

increased segregation in concrete. The absorption of gravel obtained was 1.64%. The

absorption of fine aggregate generally varies in the range of 0.5 to 4.5% [Neville

2008][115]. Thus, the absorption of gravel was in the lower range, which is good for

http://en.wikipedia.org/wiki/Quarry

http://en.wikipedia.org/wiki/Limestone

http://en.wikipedia.org/wiki/Granite

http://en.wikipedia.org/wiki/Marble

http://en.wikipedia.org/wiki/Bedrock

http://en.wikipedia.org/wiki/Mining

http://en.wikipedia.org/wiki/Barge

http://en.wikipedia.org/wiki/Truck

http://en.wikipedia.org/wiki/Concrete



concretes. A higher absorption value is indicative of greater pores in aggregates that

might affect the strength and durability of concretes.

The coarse aggregates used were air-dried. There was no free or surface moisture on

the surface of aggregates. Therefore, the concrete stone contained a negligible

amount of total evaporable moisture. The moisture content of coarse aggregates is

generally not considered in the primary mixture proportions of concrete. But the

moisture content increases the quantity of mixing water that produces a higher W/B

ratio and thus produces an impact on the properties of concrete. Hence, the

moisture content of the aggregates should be given due allowance to adjust the

mixture proportions of concrete.

Table 3.6: Properties of Coarse Aggregate-Gravel

Property Value of Graval

Source Sevalia, Gujarat




Colour Greyish Black

Absorption 1.34%


3.2.4 Water

Water is an important ingredient of concrete as it actively participates in the

chemical reaction with cement. In practice normally if water is fit for drinking it is

considered suitable for making concrete but it may not be true always. Water with

pH value between 6 to 8 is acceptable but the best coarse to find out whether a

particular source of water is suitable for concrete or not. If the compressive strength

is upto 90 percent, the source is acceptable. [Shetty 2009][150]. IS:456- [2000][58]

specifies the permissible limits for solids in water used for making concrete.

We have used normal tap water for making concrete. The tap water did not contain

any objectionable substances causing color or odor. The water was not tested to

verify the acceptance criteria based on the physical tests assuming that the quality

of potable water is acceptable for making concrete.



3.2.5 Sea water

Now-a-days, as a progress of development, lots of engineering construction including

high rise building, embankment walls, bridge etc is going on along the coastal belt of

the country. In coastal areas, there has always been a deficiency of plain water as

the available water is affected by sea salts. So it is difficult to arrange plain water for

construction works in such location. Also it is economical to use sea water that is

available near the construction site instead of plain water to be transported from

other areas/sources. But sea water contains large amounts of sea salts, which may

have adverse effect on the properties of concrete. So it is required to investigate the

effect of sea salts on strength properties of different types of concrete while using

sea water for casting and curing of concrete particularly effect on SCC. Primarily the

study is to investigate the strength behavior of concrete cured with plain as well as

sea water and compare their results.

3.2.5.1 Properties of Sea water

The sea water used for studies was brought from Mahi estuary of gulf of Khambhat.

A laboratory testing was carried out at environmental laboratory for a sample. The

properties of the sea water have been presented in Table 3.7.

Table 3.7: Properties of Sea water

Property Value As per [Deshkar 2011][28A]

Source Mahi estuary, Gulf of

Khambhat, India

Mahi estuary, Gulf of

Khambhat, India

pH 7.9 7.6-10.7

Salinity 3.69 0.2-33.10

Cl (mg/l) 8.04 0.11-18.3

NO2 (mg/l) 0.01 0.011 -0.02

NO3 (mg/l) 0.18 0.092-0.31

PO4 (mg/l) 0.15 0.1-0.21

Silicates (mg/l) 0.01 0.003-0.01

3.2.6 Admixtures

Admixture is defined as a material, other than cement, water and aggregates, which

is used as an ingredient of concrete and is added immediately before or during

mixing. It is a material which is added at the time of grinding cement clinker at the



cement factory. Various admixtures are categorized based on their function in the

concrete namely Plasticizers, Superplasticizers, Retarders and Retarding Plasticizers,

Accelerators and Accelerating Plasticizer, Air-entraining Admixtures, Damp-proofing

and Waterproofing Admixtures, Gas forming Admixtures, Workability Admixtures,

Grouting Admixtures, Bonding Admixtures, Coloring Admixtures. [Shetty 2009][150]

[IS:9103- 1999][67]

3.2.6.1 Superplasticizers or High Range Water Reducers (HRWR)

Superplasticizers (High Range Water Reducers) are low molecular-weight, water-

soluble polymers designed to achieve high amounts of water reduction (12-30%) in

concrete mixtures in order to attain a desired slump. They also can be used without

water reduction to produce concretes with very high slumps, in the range of 150 to

250 mm (6 to 10 inches). At these high slumps, concrete flows like a liquid and can

fill forms efficiently, requiring very little vibration. These highly workable mixtures

are called flowing concretes and require slumps to be in excess of 190 mm (8.5

inches). [Tandirli et al. 2000][157]. Superplasticizer (SP) also called High Range Water

Reducers (HRWR) is an essential component of SCC to provide the necessary

workability [Okamura and Ouchi 2003][116]. They reduce the yield stress and plastic

viscosity of concrete by their liquefying action.

The superplasticizer to be selected should have:

(i) High dispersing effect for low W/ P ratio (less than 1 by volume)

(ii) The dispersing effect should be maintained of for at least two hours after

mixing,

(iii) Less sensitivity to temperature changes

The main purpose of using a superplasticizer is to produce flowing concrete with

very high slump that is to be used in heavily reinforced structures and in places

where adequate consolidation by vibration cannot be readily achieved. The ability of

a superplasticizer to increase the slump of concrete depends on such factors as the

type, dosage, and time of addition, water / binder ratio and the nature of cement

and filler materials. It has been found that for most types of cement, a

superplasticizer improves the workability of concrete. The new generation



superplasticizer are Poly- Carboxylate Ether (PCE) based particularly useful for

production of SCC. [Shetty 2009][150].

The action of plasticizers is mainly to fluidify the mix and improve the workability of

concrete, mortar or grout. The mechanisms that are involved could be explained as

shown in fig. 3.3.

Using PCE polymers, give excellent water reduction as compared to normal

plasticizers. This helps to reduce the w/c ratios and cement contents, even in normal

concretes. Lower the w/c ratio, lower are the number of capillaries in concrete. It is

also a well documented fact that PCE based admixtures do not have the side effects

of retardation often seen with normal retarding superplasticizers. This is beneficial as

workability time of concrete can be controlled but the hydration and setting of

concrete will proceed unhindered. This ensures that any subsequent vibration to

concrete after initial set will not open up capillaries, as is the case if concrete is

retarded for a very long period of time, thereby rendering concrete relatively

waterproof.

Fig. 3.3: Effect of surface-active agents on deflocculating of cement grains [Shetty 2009]

[150]

Fig. 3.4 shows the structure and functioning of the latest PCE Polymer molecules.

[Surlaker 2011][156]

Superplasticizers constitute a relatively new category and improved version of

plasticizer, the use of which was developed in Japan and Germany during 1960 and

1970 respectively. They are chemically different from normal plasticizers. Use of

Superplasticizers permits the reduction of water to the extent up to 30 per cent



without reducing workability in contrast to the possible reduction up to 15 per cent

in case of plasticizers.

Fig. 3.4: Structure and Functioning of PCE Polymer

Molecules, [Surlaker 2011][156]

Superplasticizer (SP) also called High Range Water Reducers (HRWR) is an essential

component of SCC to provide the necessary workability [Okamura and Ouchi

2003][116]. They reduce the yield stress and plastic viscosity of concrete by their

liquefying action [Skarendahl and Petersson 2000][151]. The new generation

superplasticizer are Poly- Carboxylate Ether (PCE) based particularly useful for

production of SCC. [Shetty 2009][150].

3.2.6.2 Classification of superplasticizers

Following are a few polymers which are commonly used as base for

superplasticizers:

Sulphonated malanie-formaldehyde condensates (SMF)

Sulphonated naphthalene-formaldehyde condensates (SNF)

Modified lignosulphonates (MLS)

Acrylic polymer based (AP)

Copolymer of carboxylic acrylic acid with acrylic ester (CAE)

Cross linked acrylic polymer (CLAP)



Polycarboxylate ethers (PCE)

Multicarboxylat ethers (MCE)

Combinations of above.

Out of the above new generation superplasticizers based on carboxylic acrylic ester

(CAE)(Fig. 3.5) and multicarboxylatether (MCE).

As far as our country is concerned, at present, we manufacture and use the first four

types of superplasticizers. The new generation superplasticizers have been tried in

recent projects, but it was not found feasible for general usage on account of high

cost. The first four categories of products differ from one another because of the

base component or on account of different molecular weight. As a consequence

each commercial product will have different action on cements. Whilst the dosage of

conventional plasticizers do not exceed 0.25% by weight of cement in case of

lignosulphonates, or 0.1 % in case of carboxylic acids, the products of type SMF or

NSF are used considerably high dosages (0.5%-3.00%), since they do not entrain air.

Fig. 3.5: Effect of 3rd

generation PCE based super-plasticizer

The modified lignosulphonate (LS) based admixtures, which have an effective

fluidizing action, but at the relatively high dosages, they can produce undesirable

effects, such as accelerations or delay in setting times. Moreover, they increase the

air-entrainment in concrete.

Plasticizers and superplasticizers are water based. The solid contents can vary to any

extent in the products manufactured by different companies. Cost should be based

on efficiencies and solid content, but not on volume or weight basis. Generally in

projects cost of superplasticizers should be worked for one cubic meter of concrete.



3.2.6.3 Effects of superplasticizers on fresh concrete:

It is to be noted that dramatic improvement in workability is not showing up when

plasticizers or superplasticizers are added to very stiff or what is called zero slump

concrete at nominal dosages. A mix with an initial slump of about 2 to 3 cm can only

be fluidized by plasticizers or superplasticizers at nominal dosages. A high dosage is

required to fluidify no slump concrete. An improvement in slump value can be

obtained to the extent of 25 cm or more depending upon the initial slump of the

mix, the dosage and cement content. It is often noticed that slump increases with

increase in dosage. But there is no appreciable increase in slump beyond certain limit

of dosage. As a matter of fact, the over dosage may sometime harm the concrete. A

typical curve, showing the slump and dosage is shown in Fig. 3.6.

Fig. 3.6: Slump produced by superplasticizers [Shetty 2009][150]

3.2.6.4 Compatibility of superplasticizers and cement:

It has been noticed that all superplasticizers are not showing the same extent of

improvement in fluidity with all types of cements. Some superplasticizers may show

higher fluidizing effect on some type of cement than other cement. There is nothing



wrong with either the superplasticizer or that of cement. The fact is that they are

just not compatible to show maximum fluidizing effect. Optimum fluidizing effect at

lowest dosage is an economical consideration. Giving maximum fluidizing effect for a

particular superplasticizer and cement is very complex involving many factors like

composition of cement, fineness of cement etc.

Although compatibility problem looks to be very complex, it could be more or less

solved by simple rough and ready field method. Incidentally this simple field test

shows also the optimum dose of the superplasticizer to the cement. Following

methods could be adopted.

Marsh cone test

Mini slump test

Flow table test

Out of the above, Marsh cone test gives better results. In the Marsh cone test,

cement slurry is made and its flowability is found out. In concrete it is the cement

paste that influences flowability. Although, the quantity of aggregates, its shape and

texture etc. will have some influence, it is the paste that will have greater influence.

The presence of aggregate will make the test more complex and often erratic.

Whereas the using of grout alone will make the test simple, consistent and indicative

of the fluidifying effect of superplasticizer with a cement.

3.2.6.5 Selection of superplasticizer and fixation of doses

In order to identify an appropriate superplasticizer, a market survey was carried out

for number of available superplasticizers considering their properties and

availability. Three different superplasticizers were identified namely Glanium Sky

784, Viscocrete 20HE and Glenium SKY B276 suretch from two different

manufacturers. Marsh cone test was conducted to finalize one superplasticizer

amongst the identified three.

3.2.6.6 Properties of selected superplasticizers

The properties of the superplasticizer, Polycarboxylic either based, Glenium Sky-784,

Viscocrete 20HE and Glenium SKY B276 Suretch are listed in Table 3.8. The

superplasticizer is procured from BASF chemical (India) Pvt. Ltd., Sikka, India.



Table 3.8: Properties of Superplasticizers

Property Glenium Sky-784 Viscocrete 20HE Glenium SKY B276-suretch

Color Light brown liquid Light brownish liquid Light brown liquid

Relative Density 1.10 ± 0.01 at 25° C 1.08 at 25° C 1.10 ± 0.02 at 25° C

pH ≥6 4.3 ± 0.5 ≥6

Chloride ion content <0.2% Chloride-free <0.2%

3.2.7 Marsh cone test

Marsh cone apparatus is a conical brass vessel, which has a smooth aperture at the

bottom of diameter 5mm. The profile of the apparatus is shown in Fig. 3.7.

Fig. 3.7: Marsh Cone Test in progress

The procedure of test is as under:

Take 2 kg cement, proposed to be used at the project. Take one liter of water (w/c =

0.5) and start with minimum percentage of superplasticizers, say 0.1% of wt of

cement. Mix them thoroughly in a mechanical mixer (Hobart mixer is preferable) for

two minutes. Hand mixing does not give consistent results because of unavoidable

lump formation which blocks the aperture. Take one litre of cement slurry and pour

it into marsh cone duly closing the aperture with a finger. Start a stop watch and

simultaneously remove the finger. Find out the time taken in seconds, for complete

flow out of the slurry from the cone. The time in seconds is called the "Marsh Cone

Time". Repeat the test with gradually increasing the dosages of superplasticizer.

Every time the dosage of superplasticizer is increased it will be observed that the

flow time decreases. If we keep on increasing the dosage of superplasticizer, a stage



will come when increase in dosage of superplasticizer will not decrease the time of

flow. The dose at which the Marsh cone time is lowest is called the saturation point.

The dose is the optimum dose for that brand of cement and superplasticizer.

For the selected superplasticizers the Marsh cone test was carried out as narrated

above. The results are tabulated in Table 3.9. Fig. 3.8 to 3.10 show graphs for

percentage superplasticizer dosage V/s flow time indicating the saturation point and

thus showing the optimum dosage for that superplasticizer.

Table 3.9: Marsh cone flow time in seconds

SP % Glenium SKY

784

Viscocrete

20HE

Glenium SKY

B276 Suretec

0.6 168 XXX 188

0.7 104 117 122

0.8 77.30 83 93

0.9 62.45 67 73

1.0 50.38 58.23 63.25

1.1 40.56 52.56 58.47

1.2 38.54 47.12 58.30

1.3 38.57 41.03 57.8

1.4 38 40.67 XXX

1.5 XXX 39.96 XXX

It can be observed from the graph that the optimum dose for Glenium Sky 784,

Viscocrete and Glenium SKY B276 Suretch is 1.2, 1.3 and 1.1 % respectively. As

Glenium SKY B276 Suretch gives the minimum dose, we have selected it for all the

further castings of the research work.

As discussed above the reference mix are prepared using this Glenium SKY-B276-

Suretec superplasticizer with a dose of 1.1 percent of the cement.



Fig. 3.8: Superplasticizer dosage V/s flow time for Glenium SKY 784

Fig. 3.9: Superplasticizer dosage V/s flow time for Viscocrete 20HE

Fig. 3.10: Superplasticizer dosage V/s flow time for Glenium SKY B276 Suretec

saturation point

0

25

50

75

100

125

150

175

200

0.6 0.7 0.8 0.9 1 1.1 1.2 1.3 1.4

Flo

w T

ime

in s

ec

SP dosage % by cement

0.6

0.7

0.8

0.9

1

1.1

1.2

1.3

1.4

saturation point

0

25

50

75

100

125

0.7 0.8 0.9 1 1.1 1.2 1.3 1.4 1.5

Flo

w T

ime

in s

ec


0.8

0.9

1

1.1

1.2

1.3

1.4

1.5

saturation point

0

25

50

75

100

125

150

175

200

0.6 0.7 0.8 0.9 1 1.1 1.2 1.3

Flo

w T

ime

in s

ec


0.6

0.7

0.8

0.9

1

1.1

1.2

1.3



3.2.8 Self curing Admixtures

Some specific water-soluble chemicals added during the mixing can reduce water

evaporation from and within the set concrete, making it ‘self-curing.’ The chemicals

should have abilities to reduce evaporation from solution and to improve water

retention in ordinary Portland cement matrix. Internal curing (IC) is a method to

provide the water to hydrate all the cement, accomplishing what the mixing water

alone cannot do. [Dhir et al. 1994][30]

A common feature of all the existing curing techniques is that they require “external

action” to ensure that they are correctly applied for the curing of concrete. An

“internal curing system would have several advantages, primarily the production of a

better quality concrete surface, greater turnover and the reduction in costs of

operatives. It is conceivable that such a system could be created by the introduction

during the mixing state of a chemical that would reduce water evaporation in the set

concrete and make the concrete effectively “self-curing”.

3.2.8.1 Super-absorbent Polymer (SAP) for self curing

SAPs are a group of polymeric materials that have the ability to absorb a significant

amount of liquid from the surroundings and to retain the liquid within their structure

without dissolving. SAPs are principally used for absorbing water and aqueous

solutions. SAPs can be produced with water absorption of up to 5000 times their

own weight. However, in dilute salt solutions, the absorbency of commercially

produced SAPs is around 50 g/g. They can be produced by either solution or

suspension polymerization, and the particles may be prepared in different sizes and

shapes including spherical particles. Because of their ionic nature and

interconnected structure, they can absorb large quantities of water without

dissolving. SAPs exist in two distinct phase states, collapsed and swollen. The

macromolecular matrix of a SAP is a polyelectrolyte, i.e., a polymer with ionisable

groups that can dissociate in solution, leaving ions of one sign bound to the chain

and counter-ions in solution. For this reason, a high concentration of ions exists

inside the SAP leading to a water flow into the SAP due to osmosis. Another factor



contributing to increase the swelling is water solvation of hydrophilic groups present

along the polymer chain. Elastic free energy opposes swelling of the SAP by a

detractive force. [Ambily and Rajamane 2007][12]

The common SAPs are added at rate of 0–0.6 wt % of cement. The SAPs are

covalently cross-linked. They are Acrylamide/acrylic acid copolymers. One type of

SAPs are suspension polymerized, spherical particles with an average particle size of

approximately 200 mm; another type of SAP is solution polymerized and then

crushed and sieved to particle sizes in the range of 125–250 mm. The size of the

swollen SAP particles in the cement pastes and mortars is about three times larger

due to pore fluid absorption. The swelling time depends especially on the particle

size distribution of the SAP. It is seen that more than 50% swelling occurs within the

first 5 min after water addition. [Naik and Canpolat 2006][108]

Experimental measurements were performed to predict the compressive strength,

split tensile strength and flexural strength of the concrete containing Super

Absorbent Polymer (SAP) at a range of 0%, 0.2%, 0.3%, and 0.4% of cement and

compared with that of cured concrete of grade M40. Addition of SAP leads to a

significant increase of mechanical strength (Compressive, split tensile and flexural

strength). From the results it was noted that the compressive strength increased by

28%, 34% and 2.16% at 3days and 32.8%, 36.5% and23% at 7 days and 2.5%, 7.23% and

6.34% at 28 days respectively for the Mix2, Mix3 and Mix4 when compared to control

mix. The split tensile strength increased by 8.5%, 20.5% and 2.56% at 3days and 2%,

15.73% and 6.5% at 7 days and 15%, 18.6% and 4.64% at 28 days respectively for the

Mix2, Mix3 and Mix4 when compared to control mix. The flexural strength increased by

7.56%,11.68% and 10.4% at 3 days, 7 days and 28 days respectively for the Mix 2, Mix3

and Mix4 when compared to controlled mix. Maximum Compressive, tensile and

flexural strength of self curing concrete for dosage of SAP 0.3% of cement was higher

than non self curing concrete. [Francis and John 2013][40]. He also noted that

performance of the self-curing agent was affected by the mix proportions mainly the

cement content and the w/c ratio.



3.2.8.2 Polyethylene Glycols (PEGs)

Use of poly-ethylene glycol (PEG) reduces the evaporation of water from the surface

of concrete and also helps in water retention. Polyethylene glycol is a condensation

polymer of ethylene oxide and water with the general formula H(OCH2CH2)nOH, the

abbreviation (PEG) is termed in combination with a numeric suffix which indicates

the average molecular weights. One common feature of PEG appears to be the

water-soluble nature. Polyethylene glycol is non-toxic, odorless, neutral, lubricating,

non-volatile and non-irritating and is used in a variety of pharmaceuticals. Depending

on the number of oxyethylene groups, the molecular weight ranges from 200 to

approximately 9500. PEG's below 700 molecular weight occur as clear to slightly

hazy, colorless, slightly hygroscopic liquids with a slight characteristic odour. PEG's

Between 700-900 are semi-solid. PEG's over 1000 molecular weight are creamy

white waxy solids, flakes, or free-flowing powders. [Macrogol 1992][96].

The extent of polyethylene glycol absorption appears to be dependent on the

molecular weight of the specific polymer, such that more complete absorption has

been reported for the lower weight polyethylene glycols, while absorption is much

more limited in the case of the higher molecular weight polyethylene glycols.

3.2.8.3 Properties PEGs selected for studies and its doses

In order the study the effect of molecular weight of the curing capacity we have

selected two PEGs with different molecular weight namely PEG600 (Fig. 3.11) and

PEG1500 (Fig. 3.12). The chemicals are procured from Merck (India) Ltd, Mumbai,

India. The properties of are shown in table 3.10. Dosages of PEG’s was decided with

reference to relevant literature review and fixed as 0.5% of cementitious material.

[Ambily 2007][12] [Sathanandham et al. 2013][145].

Fig. 3.11: PEG 600 LR Fig. 3.12: PEG1500 for self curing A2 type



Table 3.10: Properties of PEG600 & PEG1500

Property PEG600 PEG1500

Physical State And Appearance Liquid, Transparent Flakes, creamy white

Odor & Taste Not Available Not available

Molecular Weight 600 G/Mole 1500 G/Mole

Ph (1% Soln/Water) 6 6

Specific Gravity 1.12 1.1

Dispersion Properties Solubility in water, Methanol, Diethyl Ether

Solubility in water, Methanol, Diethyl Ether

Solubility Easily Soluble in cold water, Hot water. Soluble in Methanol, Diethyl Ether

Easily Soluble in cold water, Hot water. Soluble in Methanol, Diethyl Ether

3.2.9 Membrane-forming curing chemicals:

Membrane-forming compounds consisting of waxes, resins, chlorinated rubber, and

other materials can be used to retard or reduce evaporation of moisture from

concrete. They are the most practical and most widely used method for curing not

only freshly placed concrete but also for extending curing of concrete after removal

of forms or after initial moist curing. Curing compounds should be able to maintain

the relative Humidity of the concrete surface above 80% for seven days to sustain

cement hydration. [Goel et al. 2013][43]

Membrane-forming curing compounds are of two general types: clear, or

translucent; and white pigmented. Clear or translucent compounds may contain a

fugitive dye that makes it easier to check visually for complete coverage of the

concrete surface when the compound is applied. The dye fades away soon after

application. On hot, sunny days, use of white-pigmented compounds is

recommended; they reduce solar-heat gain, thus reducing the concrete

temperature. Pigmented compounds should be kept agitated in the container to

prevent pigment from settling out. Curing compounds should be applied by hand-

operated or power-driven spray equipment immediately after final finishing of the

concrete. The concrete surface should be damp when the coating is applied. On dry,

windy days, or during periods when adverse weather conditions could result in

plastic shrinkage cracking, application of a curing compound immediately after final

finishing and before all free water on the surface has evaporated will help prevent

the formation of cracks. [Shetty 2009][150]

Power-driven spray is recommended for uniform application of curing compounds



on large paving projects. Spray nozzles and windshields on such equipment should

be arranged to prevent wind-blown loss of curing compound. Normally only one

even coat is applied at a typical rate of 3 to 4m2 per litre but products may vary, so

manufacturer’s recommended application rates should be followed. If two coats are

necessary to ensure complete coverage, second coat should be applied at right

angles to the first. Complete coverage of the surface must be attained because even

small pinholes in the membrane will increase the evaporation of moisture from the

concrete.

Curing compounds might prevent bonding between hardened concrete and a freshly

placed concrete overlay. And, most curing compounds are not compatible with

adhesives used with floor covering materials. And, most curing compounds are not

compatible with adhesives used with floor covering materials. Consequently, they

should either be tested for compatibility, or not used when bonding of overlying

materials is necessary. [Neville 2008][115]

Table 3.11: Properties of Wax based curing

compound – FAIRCURE as per ASTM

Water retention 0.29% kg/m²

Reflectance 70 %

Drying time < 90 min

Water retention

efficiency

More than 90%

Curing efficiency 90%

Fig. 3.13: Wax Based Curing Compound

FAIRCURE WX WHITE and its application

For external curing compound, a wax based chemical with brand name FAIRCURE

WX WHITE procured from FAIR MATE chemical Pvt. Ltd , Mumbai, India was used.

The properties of material are listed in table 3.11. Wax based liquids FAIRCURE

(Fig.3.13) was sprayed with brush in two layers over the freshly finished specimen

once the free water on the surface has evaporated and there was no water sheen on

the surface visible on the specimens. This liquid forms an impermeable membrane

that minimizes the loss of moisture from the concrete.



3.2.10 Polyethylene film

Plastic sheets such as polyethylene film are used to cure concrete. Polyethylene films

are lightweight, impervious hence prevent the moisture movement from the

concrete and can be applied to simple as well as on complex shapes. Major

disadvantage of this type of curing is that it causes patchy discoloration especially if

the concrete contains calcium chloride. Discoloration is more pronounced when the

film develops wrinkles and it is difficult and time consuming on a large project to

place the sheets without wrinkles. Polyethylene film should confirm to ASTM C171.

[ASTM-C171 2007][16]. The specimen were wrapped with a transparent 0.01 mm

thick plastic material after de-molding and are placed over the exposed surfaces of

concrete as soon a placed in a semi open place in ambient temperature. Care was

taken that at-least three wraps of sheet are placed without marring the finish of

specimens. Fig. 3.14 shows the sample specimen wrapped with polyethylene film.

Fig. 3.14: Polyethylene film wrapped specimen

3.2.11 Gunny bags for Wet covering

This is most often used curing method in the construction industry. In this method

moisture retaining fabrics such as burlap cotton mats, jute mats and rugs are used as

wet covering to keep the concrete in a wet condition during the curing period, for if

the drying is permitted, the cover will itself absorb the water from the concrete.

Alternative cycles of wetting and drying during the early period of curing will cause



cracking of the surface. The major disadvantage of this method is discolouring of

concrete.

Wet covering curing is the most efficient and preferred techniques in various

construction projects, but they also encounter certain restriction in situ in

construction of highways, canal lining, Shell structures, high-rise buildings and areas

having scarcity of water.

Locally available jute mats were used to cure the specimen. Jute mat covers were

placed as soon as the specimens were de-molded to maintain water on the surface

of the concrete. They were kept wet continuously for the period of experiments.

Care was taken to avoid alternative drying and wetting condition by continuously

keeping the mats wet with water. Fig. 3.15 shows the specimen covered with jute

mat.

Fig. 3.15: Wet covering with jute mat

CHAPTER 3 COMPOSITION OF MATERIALS FOR SELF COMPACTING...

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