A report on

PERFORMANCE OF SELF CURING CONCRETE WITH RECYCLED COARSE AGGREGATE

Done by

Project Guide

Dr. P V Indira

National Institute of Technology, Calicut

Roll No. Name of the Student Branch B080750CE MALINDU SASANKA SANDANAYAKE CIVILB080519CE LALIT KUMAR BARADWAJ CIVILB080513CE YENDURI ANURAG CIVIL

WINTER SEMESTER 2010-11

MINI PROJECT

CERTIFICATE

This is to certify that this is a bonafide record of the project presented by the students, whose names are given below, during Monsoon Semester 2010-11 in partial fulfillment of the requirement of the course on environmental studies.

Dr. P V Indira

Project Guide

Dr. Mini Remanan

Course Coordinator

ACKNOWLEGEMENTS

Roll No. Name of the Student Branch B080750CE MALINDU SASANKA SANDANAYAKE CIVILB080519CE LALIT KUMAR BARADWAJ CIVILB080513CE YENDURI ANURAG CIVIL

We would like to thank the following for their kind support and valuable information provided without whom it would have been impossible to complete the project successfully.

Dr. Mini Remanan, faculty incharge of Mini Project Course for giving us this opportunity.

Dr. P V Indira, faculty guide for the project for her guidance and moral support. Mr. Y. Vijaya Bhaskar, M. Tech 2nd year, NIT Calicut for providing valuable information

regarding our project.

THANK YOU

Group Members

BRIEF DESCRIPTION OF THE WORK PROPOSED AND METHODOLOGY:

INTRODUCTION:

properties (compressive strength, split tensile strength, flexure strength) of self curing concrete with Proper curing of concrete structures is important to ensure they meet their intended performance and durability requirements. Internal curing (IC) is a very promising technique that can provide additional moisture in concrete for a more effective hydration of the cement. During hydration of cement, empty pores are created within the cement paste, leading to a reduction in its internal relative humidity and cause cracks to develop at the early-age. This situation is intensified in HPC which can be solved by using the self curing agents like polyethylene glycol as they can retain the moisture for a long period of time.

Depletion of natural coarse aggregate and disposal of construction and demolition waste are currently two problems of increasing magnitude, faced by infrastructure development sector. Recycling demolished concrete waste as an alternative source of coarse aggregate for the production of new concrete can help solve simultaneously the growing waste disposal crisis and the problem of short supply of natural coarse aggregate for concrete. This practice leads to eagerly awaited and preservation of environment to escape from climate disasters. Under the pressure of these problems, several studies are reported in different countries on recycled coarse aggregate.

OBJECTIVE OF THE PROJECT:

Our investigation is presented on evaluating the structural recycled coarse aggregate (RCA) and concrete with conventional coarse aggregate (CCA), for comparison.

METHODOLOGY:

To acquire knowledge on self curing concrete with RCA, 12 cube specimens will be cast and tested for determining the compressive strength, 12 cylinder specimens will be cast and tested for determining the split tensile strength, 2 beams will be cast and tested for flexural strength and the above procedure is repeated for concrete with conventional coarse aggregate, for comparison.

INDEX

Chapters:

1. Introduction1.1 General1.2 Recycled aggregate1.3 Polyethylene glycol

2. Literature Review2.1 Self curing of concrete using self curing agents2.2 Self curing of concrete using LWA

3. Experimental Programme3.1 Materials used3.2 Casting programme3.3 Testing programme3.4 Experimental investigations

4. Results and Discussion4.1 Effect of PEG 600 on properties of concrete4.2 Effect of recycled coarse aggregate on properties of concrete

5. Conclusion

CHAPTER – 1

INTRODUCTION

1.1 GENERAL

Proper curing of concrete structures is important to ensure they meet their intended performance and durability requirements. In conventional construction, this is achieved through external curing, applied after mixing, placing and finishing. Internal curing (IC) is a very promising technique that can provide additional moisture in concrete for a more effective hydration of the cement and reduced self-desiccation. Internal curing implies the introduction of a curing agent into concrete that will provide this additional moisture. Currently, there are two major methods available for internal curing of concrete. The first method uses saturated porous lightweight aggregate (LWA) in order to supply an internal source of water, which can replace the water consumed by chemical shrinkage during cement hydration. The second method uses super-absorbent polymers (SAP), as these particles can absorb a very large quantity of water during concrete mixing and form large inclusions containing free water, thus preventing self-desiccation during cement hydration. For optimum performance, the internal curing agent should possess high water absorption capacity and high water desorption rates. Detailed information on internal curing can be found in the new state-of-the-art report on internal curing of concrete from RILEM TC-196.

1.1.1 Definition of Internal Curing (IC)

The ACI-308 Code states that “internal curing refers to the process by which the hydration of cement occurs because of the availability of additional internal water that is not part of the mixing Water.” Conventionally, curing concrete means creating conditions such that water is not lost from the surface i.e., curing is taken to happen ‘from the outside to inside’. In contrast, ‘internal curing’ is allowing for curing ‘from the inside to outside’ through the internal reservoirs (in the form of saturated lightweight fine aggregates, superabsorbent polymers, or saturated wood fibres) created. ‘Internal curing’ is often also referred as ‘Self–curing.’

1.1.2 Need for Self–curing

When the mineral admixtures react completely in a blended cement system, their demand for curing water (external or internal) can be much greater than that in a conventional ordinary Portland cement concrete [10]. When this water is not readily available, due to depercolation of the capillary porosity, for example, significant autogenous deformation and (early-age) cracking may result.

Due to the chemical shrinkage occurring during cement hydration, empty pores are created within the cement paste, leading to a reduction in its internal relative humidity and also

to shrinkage which may cause early-age cracking. This situation is intensified in HPC (compared to conventional concrete) due to its generally higher cement content, reduced water/cement (w/c) ratio and the pozzolanic mineral admixtures (fly ash, silica fume). The empty pores created during self-desiccation induce shrinkage stresses and also influence the kinetics of cement hydration process, limiting the final degree of hydration. The strength achieved by IC could be more than that possible under saturated curing conditions.

Often specially in HPC, it is not easily possible to provide curing water from the top surface at the rate required to satisfy the ongoing chemical shrinkage, due to the extremely low permeabilities often achieved.

1.1.3 Mechanism of Internal Curing

Continuous evaporation of moisture takes place from an exposed surface due to the difference in chemical potentials (free energy) between the vapour and liquid phases. The polymers added in the mix mainly form hydrogen bonds with water molecules and reduce the chemical potential of the molecules which in turn reduces the vapour pressure, thus reducing the rate of evaporation from the surface.

1.1.4 Potential Materials for Internal Curing (IC)

The following materials can provide internal water reservoirs:

Lightweight Aggregate (natural and synthetic, expanded shale), LWS Sand (Water absorption =17 %) LWA 19mm Coarse (Water absorption = 20%) Super-absorbent Polymers (SAP) (60-300 mm size) SRA (Shrinkage Reducing Admixture) (propylene glycol type i.e. polyethylene-glycol) Wood powder

1.1.5 Chemicals to Achieve Self–curing

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.

1.1.6 Super-absorbent Polymer (SAP) for Internal Curing (IC)

The common SAPs are added at rate of 0–0.6 wt % of cement. They are Acrylamide/acrylic acid copolymers. 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. The commercially important SAPs are covalently cross-linked poly acrylates and copolymerized poly acrylamides/ poly acrylates. Because of their ionic nature and interconnected structure, they can absorb large quantities of water without dissolving. From a chemical point of view, all the water inside a SAP can essentially be considered as bulk water. SAPs exist in two distinct phase states, collapsed and swollen.

1.1.7 Means of Providing Water for Self–curing using Light Weight Aggregates

Water/moisture required for internal curing can be supplied by incorporation of saturated-surface dry (SSD) lightweight aggregates (LWA).

1.1.8 Water in LWA for Internal Curing

About 67% of the water absorbed in the LWA can get transported to self-desiccating paste [10]. Some water remains always in the LWA in the high RH range and it becomes useful when the overall RH humidity in concrete is significantly reduced. The water retained in LWA in air-dry condition may not be enough to prevent autogenous shrinkage whose magnitude, however, may be reduced significantly. The fine lightweight aggregate, in saturated condition, produce a more uniform distribution of the water needed for curing throughout the microstructure.

1.1.9 Monitoring of Self – Curing

This can be done by:

1. Measuring weight-loss

2. X-Ray powder diffraction

3. X-Ray micro chromatography

4. Thermogravimetry (TGA) measurements

5. Initial surface absorption tests (ISAT)

6. Compressive strength

7. Scanning electron microscope (SEM)

8. Change internal RH with time

9. Water permeability

10. NMR spectroscopy

1.1.10 Advantages of Internal Curing

a. Internal curing (IC) is a method to provide the water to hydrate all the cement, accomplishing what the mixing water alone cannot do. In low w/c ratio mixes (under 0.43 and increasingly those below 0.40) absorptive lightweight aggregate, replacing some of the coarse aggregates, provides water that is desorbed into the mortar fraction (paste) to be used as additional curing water. The cement, not hydrated by low amount of mixing water, will have more water available to it.

b. IC provides water to keep the relative humidity (RH) high, keeping self-desiccation from occurring.

c. IC eliminates largely autogenous shrinkage.

d. IC maintains the strengths of mortar/concrete at the early age (12 to 72 hrs.) above the level where internally & externally induced strains can cause cracking.

e. IC can make up for some of the deficiencies of external curing, both human related (critical period when curing is required in the first 12 to 72 hours) and hydration related (because hydration products clog the passageways needed for the fluid curing water to travel to the cement particles thirsting for water). Following factors establish the dynamics of water movement to the unhydrated cement particles:

i. Thirst for water by the hydrating cement particles is very intense,

ii. Capillary action of the pores in the concrete is very strong, and

iii. Water in the properly distributed particles of LWA (fine) is very fluid.

1.1.11 Concrete Deficiencies that IC can address

The benefit from IC can be expected when

Cracking of concrete provides passageways resulting in deterioration of reinforcing steel,

Low early-age strength is a problem,

Permeability or durability must be improved,

Rheology of concrete mixture, modulus of elasticity of the finished product or durability of high fly-ash concretes are considerations.

Need for: reduced construction time, quicker turnaround time in precast plants, lower maintenance cost, greater performance and predictability.

1.1.12 Improvements to Concrete due to Internal Curing

Reduces autogenous cracking,

Largely eliminates autogenous shrinkage,

Reduces permeability,

Protects reinforcing steel,

Increases mortar strength,

Increases early age strength sufficient to withstand strain,

Provides greater durability,

Higher early age (say 3 day) flexural strength

Higher early age (say 3 day) compressive strength,

Lower turnaround time,

Improved rheology

Greater utilization of cement,

Lower maintenance,

Use of higher levels of fly ash,

Higher modulus of elasticity, or

Through mixture designs, lower modulus

Sharper edges,

Greater curing predictability,

Higher performance,

Improves contact zone,

Does not adversely affect finishability,

Does not adversely affect pumpability,

Reduces effect of insufficient external curing.

1.1.13 Distribution of Internal Water Reservoirs for Curing

The transport distance of water within the concrete is limited by de-percolation of the capillary pores in low w/c ratio pastes. With water-reservoirs well distributed within the matrix, shorter distances have to be covered by the curing water and the efficiency of the internal-curing process is consequently improved. The concept of internal curing was established, based on dispersion of very small, saturated LWA throughout the concrete, which serve as tiny reservoirs with sufficient water to compensate for self-desiccation. The spacing between the LWA particles is conveniently small so that the water travels smaller distances to counteract self-desiccation. The amount of water in the LWA can therefore be minimized, thus economising on the content of the LWA.

1.1.14 Usefulness of IC for Early-Age Cracking

The IC can influence the ‘Early- Age Cracking Contributors’ which are mainly thermal effects and autogenous shrinkage. During initial ages of concrete, hydration heat can raise concrete temperature significantly (causing expansion), subsequent thermal contraction during cooling can lead to early-age (global or local) cracking if restrained (globally or locally). Another prominent effect would be autogenous shrinkage, especially in concretes with lower water-binder ratios where sufficient curing water cannot be supplied externally, the chemical shrinkage accompanying the hydration reactions will lead to self-desiccation and significant autogenous shrinkage (and possibly cracking).

1.1.15 Quantifying Effectiveness of IC

IC can be experimentally measured by:

Internal RH

Autogenous deformation

Compressive strength development

Degree of hydration

Restrained shrinkage or ring tests

3-D X-ray micro tomography (Direct observation of e 3-D microstructure of cement-based materials).

1.2 RECYCLED AGGREGATE

Taking the concept of sustainable development into consideration, the concrete industry need to implement a variety of strategies with regard to future concrete use, for instance; improvement in the durability of concrete and better use of recycled materials. In general, aggregates occupy 55% to 80% of concrete volume. Without proper alternative aggregates being utilized in the near future, the concrete industry globally will consume 8 to 12 billion tonnes annually of natural aggregates after the year 2010[11]. Such large consumption of natural aggregates will cause destruction of the environment. Therefore, finding a suitable substitute for natural aggregates is an urgent task. Even though the utilization of recycled aggregates is being done in the concrete industry for many years, the promotion of this recycled material as an alternative has never been easy in the industry.

Construction and Demolition (C&D) [11] waste constitutes a major portion of total solid waste production in the world, and most of it is used in landfills. Research by concrete engineers has clearly suggested the possibility of appropriately treating and reusing such waste as aggregate in new concrete, especially in lower level applications. Initially, recycling of demolition waste was

first carried out after the Second World War in Germany (Khalaf et al.) [12]. since then, research work carried out in several countries has demonstrated sufficient promise for developing use of construction waste as a constituent in new concrete. Construction and demolition (C&D) waste could be broken concrete, bricks from buildings, or broken pavement. Thus, Recycled Aggregate (RA) could come from the demolition of buildings, bridge supports, airport runways, and concrete roadbeds. Concrete made using such aggregates is referred to as recycled aggregate concrete (RAC).

The significant research is in progress in the United States of America, the United Kingdom. And encouraging results advocating utilization recycled aggregate for construction purposes, especially for pavements of all types. Comprehensive research work is in progress at many place including India to remove these reservations, many of the above countries have started formulating their codes of standards /practice as guidelines for use of recycle aggregates for construction purpose.

The problems in India are not as alarming as in the west. However, the day would not be very far off, when India to may have to seriously think of reusing demolished rubble and concrete for production of recycled construction material especially in the form of aggregate. There some parts in northern India, especially, in the Gangetic basin, where crushed stone aggregate is not available within several kilometers of radius. Conservation of natural resources in order to keep ecological balance is the need for India too.

Processing of recycled material is a relatively simple process, but one that can require expensive, heavy-duty equipment, capable of handling a variety of materials. Technology basically involves crushing, sizing, and blending to meet the required product mix. The schematic diagram of the recycled processing plant is shown in fig2.

1.2.1 Advantages of Recycled aggregate:

There are many advantages through using the recycled aggregate. The advantages that occur through usage of recycled aggregate are listed below.

• Environmental Gain

The major advantage is based on the environmental gain. Construction and demolition waste makes up to around 40% of the total waste each year (estimate around 14 million tons) going to land fill. Through recycled these material, it can keep diminishing the resources of urban aggregated. Therefore, natural aggregate can be used in higher grade applications.

• Save Energy

The recycling process can be done on site. According to Kajima Technical Research Institute (2002), Kajima is developing a method of recycling crushed concrete that used in the construction, known as the Within-Site Recycling System. Everything can be done on the construction site through this system, from the process of recycled aggregate, manufacture and use them. This can save energy to transport the recycled materials to the recycling plants.

• Cost

Secondly is based on the cost. The cost of recycled aggregate is cheaper than virgin aggregate. It depends on the aggregate size limitation and local availability. This is just around one and half of the cost for natural aggregate that used in the construction works. In small scale projects, where recycling plant proves to be costlier hand broken recycled aggregates can also be used. Research is going on application of hand broken recycled aggregates.

• Sustainability

The amount of waste materials used for landfill will be reducing through usage of recycled aggregate. This will reduce the amount of quarrying. Therefore this will extend the lives of natural resources and also extend the lives of sites that using for landfill.

1.2.2 Disadvantages

Although there are many advantages by using recycled aggregate. But there are still some disadvantages in recycled aggregate.

• Lack of Specification and Guidelines

There is no specification or any guideline when using recycled concrete aggregate in the constructions. In many cases, the strength characteristic will not meet the requirement when using recycled concrete aggregate. Therefore, more testing should be considered when using recycled concrete aggregate.

• Water Pollution

The recycled process will cause water pollution. The wash out water with the high pH is a serious environmental issue. According to Building Green (1993), the alkalinity level of wash water from the recycling plants is pH=12. This water is toxic to the fish and other aquatic life.

1.3 POLYETHYLENE GLYCOL

Polyethylene glycol is a condensation polymers of ethylene oxide and water with the general formula H(OCH2CH2)nOH, where n is the average number of repeating oxyethylene groups typically from 4 to about 180. The low molecular weight members from n=2 to n=4 are diethylene glycol, triethylene glycol and tetraethylene glycol respectively, which are produced as pure compounds. The low molecular weight compounds up to 700 are colourless, odourless viscous liquids with a freezing point from -10 C (di-ethylene glycol), while polymerized compounds with higher molecular weight than 1,000 are wax like solids with melting point up to 67 C for n 180. 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. It is soluble also in many organic solvents including aromatic hydrocarbons (not aliphatic). Polyethylene glycol is non-toxic, odourless, neutral, lubricating, non-volatile and non-irritating and is used in a variety of pharmaceuticals and in medications as a solvent, dispensing agent, ointment and suppository bases, vehicle, and tablet excipient.

They are used to make emulsifying agents and detergents, and as plasticizers, humectants, and water-soluble textile lubricants. The wide range of chain lengths provides identical physical and chemical properties for the proper application selections directly or indirectly in the field of; 

Alkyd and polyester resin preparation to enhance water dispersability and water-based coatings.

Brightening effect and adhesion enhance in electroplating and electroplating process.

Cleaners, detergents and soaps with low volatility and low toxicity solvent properties.

Coupling agent, humectant, solvent and lubricant in cosmetics and personal care bases.

Dimensional stabilizer in wood working operations

Dye carrier in paints and inks

Heat transfer fluid formulation and defoamer formulations.

Low volatile, water soluble and noncorrosive lubricant without staining residue in food and package process.

Plasticizer to increase lubricity and to impart a humectants property in ceramic mass, adhesives and binders.

Soldering fluxes with good spreading property.

CHAPTER – 2

LITERATURE REVIEW

2.1 SELF CURING OF CONCRETE USING SELF CURING AGENTS

Present-day self-curing concrete can be classified as an advanced construction material. As the name suggests, it does not require to be cured in water. This offers many benefits and advantages over conventional concrete. This includes an improved quality of concrete and reduction of autogenous shrinkage. The composition of Self Curing Concrete mixes includes substantial proportions of self curing agents and saturated recycled coarse aggregate and this gives possibilities for utilization of water inside concrete. The benefit from Self Curing Concrete can be expected when there is need for reduced construction time, quicker turnaround time in precast plants, lower maintenance cost, greater performance and predictability.The use of Self Curing Concrete ensures quality and durability of concrete. In the following, a summary of the articles and papers found in the literature, about the self compacting concrete and some of the projects carried out with this type of concrete, are presented.

Ole Mejlhede Jensen, Per Freiesleben Hansen [1] describes a new concept for the prevention of self-desiccation in hardening cement-based materials. The concept consists of using fine, superabsorbent polymer (SAP) particles as a concrete admixture. The SAP will absorb water and form macro inclusions, which essentially consist of nothing but free water. This leads to water entrainment, i.e. the formation of water-filled macro pore inclusions in the fresh concrete. Consequently, the pore structure is actively designed to control self-desiccation. In his work, self-desiccation and water entrainment are described and discussed. The description is based on a reinterpretation of Powers' model for the phase distribution of a hydrating cement paste.

Roland Tak Yong Liang, Robert Keith Sun [2] carried work on internal curing composition for concrete which includes a glycol and a wax. The invention was based on the observation that a combination of a wax and a glycol, when added to concrete, enables internal curing of concrete which in many respects is equal to or superior to traditional forms of curing concrete. The invention provides for the first time an internal curing composition which, when added to concrete or other cementitious mixes meets the required standards of curing as per Australian Standard AS 3799. A preferred internal curing composition according to the invention includes a paraffin wax and a PEG of MW about 200.

Wen-Chen Jau [3] stated that “A Self Curing Concrete is provided to absorb water from moisture from air to achieve better hydration of cement in concrete. It solves the problem that the degree of cement hydration is lowered due to no curing or improper curing, and thus unsatisfactory properties of concrete. According to the invention, high-performance self-curing

agent about 0.1~5 wt % of cement weight of the concrete is added to the concrete during mixing. The self-curing agent can absorb moisture from atmosphere and then release it to concrete. The self-curing concrete means that no curing is required for concrete, or even no external supplied water is required after placing. The properties of the self-cured concrete of the invention are at least comparable to even better than those of concrete with traditional curing.” In his invention self curing agent contains poly-acrylic acid which has strong capability of absorbing moisture from atmosphere and providing water required for curing concrete and also contains polyvalent alcohol, selected from the group consisting of PEG, PG, DPG etc. His works are carried out at RH of 50% ~ 85%.

A.S. El-Dieb [4] investigated water retention of concrete using water-soluble polymeric glycol as self-curing agent. Concrete weight loss and internal relative humidity measurements with time were carried out, in order to evaluate the water retention of self-curing concrete. Non-evaporable water at different ages was measured to evaluate the hydration. Water transport through concrete is evaluated by measuring absorption%, permeable voids%, water sorptivity, and water permeability. The water transport through self-curing concrete is evaluated with age. The effect of the concrete mix proportions on the performance of self-curing concrete were investigated, such as, cement content and water/cement ratio.

Pietro Lura [5] carried work on autogenous deformation of cementitious materials and internal curing as a means to reduce early-age shrinkage and self-induced stresses. The main aim of his study was to reach a better comprehension of autogenous shrinkage in order to be able to model it and possibly reduce it. Once the important role of self-desiccation shrinkage in autogenous shrinkage is shown, the benefices of avoiding self-desiccation through internal curing become apparent.

2.2 SELF CURING OF CONCRETE USING LWA

Silvia Weber and Hans W. Reinhardt [6] in 1996-97 introduced a new type of high performance concrete by replacing 25% by volume of the aggregates by prewetted LWA which creates water storage inside the concrete, which supports continuous wet curing. The most important mechanical properties of the concrete under various curing conditions and the microstructure of the hardened cement paste were investigated. The results obtained showed that method of introducing a water reservoir can be successfully applied to obtain HPC with improved properties while being relatively insensitive to curing.

S. Zhutovsky, K. Kovler and A. Bentur [7] carried work on “Efficiency of lightweight aggregates for internal curing of high strength concrete to eliminate autogenous shrinkage”. The application of the concept of internal curing by means of saturated lightweight aggregate was applied and shown to be effective in eliminating autogenous shrinkage. Their work describes an approach to optimize the size and porosity of the lightweight aggregate to obtain effective internal curing with a minimum content of such aggregate.

M.R. Geiker, D.P. Bentz and 0.M. Jensen [8] compared two sources of internal water supply to mitigate autogenous shrinkage by IC. They are 1) replacement of a portion of the sand by partially saturated lightweight fine aggregate and 2) the addition of superabsorbent polymer particles (SAP). At equal water addition rates, the SAP system is seen to be more efficient in reducing autogenous shrinkage at later ages, most likely due to a more homogeneous distribution of the extra curing water within the three-dimensional mortar microstructure.

Daniel Cusson and Ted Hoogeveen [9] carried work on “Internal curing of high-performance concrete with pre-soaked fine lightweight aggregate for prevention of autogenous shrinkage cracking”. Internal curing was supplied by pre-soaked fine LWA as a partial replacement to regular sand. It was found that the use of 178 kg/m3 of saturated LWA in HPC, providing 27 kg/m3 of IC water eliminated the tensile stress due to restrained autogenous shrinkage without compromising the early-age strength and elastic modulus of HPC. Autogenous expansion, observed during the first day for high levels of internal curing, can significantly reduce the risk of cracking in concrete structures, as both the elastic and creep strains develop initially in compression, enabling the tensile strength to increase further before tensile stresses start to initiate later.

CHAPTER – 3

EXPERIMENTAL PROGRAMME

The experimental program was designed to investigate the strength of Self Curing of Concrete using Polyethylene Glycol-600(PEG) with 100% replacement of Natural Aggregate with Recycled Coarse Aggregate for the grade M25 on compressive strength, split tensile strength, flexure strength.

The program consisted of casting and testing a total number of 18 cubes of size 150 X 150 X 150mm, 2 cylinders, 2 beams. Of these 6 cubes each correspond to normal curing concrete with ordinary coarse aggregate, self curing concrete with ordinary coarse aggregate, self curing concrete with recycled coarse aggregate. In this 3 cubes each correspond to curing for 7 days and 28days strength. 1 cylinder and 1 beam each correspond to self curing concrete with ordinary coarse aggregate, self curing concrete with recycled coarse aggregate.

3.1 MATERIALS USED

The different materials used in this investigation are

43 Grade Ordinary Portland cement Fine Aggregate Coarse Aggregate(natural and recycled) Polyethylene Glycol-600 Water

3.1.1 Cement:

Cement used in the investigation was 43 grade ordinary Portland cement confirming IS: 12269: 1987. The cement used for experiments was obtained from a single consignment and of same grade and same source. Procuring the cement it was stored properly.

3.1.2 Fine aggregate:

The fine aggregate conforming to zone III according to IS: 383-1970 was used. The fine aggregate used was obtained from a near river source. The specific gravity of the sand used was 2.54. The sand obtained was sieved as per IS sieves (i.e. 475, 2.36, 1.18, 600, 300, and 150µ). The details of particle size distribution and grading are given in table3.1.

Table 3.1 Proportions of different size fractions of sand

Sieve size

(mm)

Weight retained

(gm)

%Weight retained

(%)

Cumulative

% weight

retained

% Passing

%passing

Recommended

By IS:383-1970

4.75 7 1.4 1.4 98.60 90-100

2.36 12 2.4 3.8 96.20 75-100

1.18 20 4.0 7.8 92.20 55-90

0.60 65 13.0 20.8 79.00 35-59

0.30 292 58.4 79.2 30.00 8-30

0.15 90 18.0 97.20 2.80 0-10

3.1.3 Coarse aggregate:

Crushed granite and RCA was used as coarse aggregate. The coarse aggregate according to IS: 383-1970 was used. Maximum coarse aggregate size used 20 mm. The details of particle size distribution and grading are given in table 3.2. Properties of natural & recycled aggregate as shown in table 3.3.

Table 3.2 Proportions of different size fractions of coarse aggregates

Sieve size

(mm)

Weight retained

(gm)

%Weight retained

(%)

Cumulative

% weight

retained

% Passing

%passing

Recommended

By IS:383-1970

40 - - - 100 100

20 - - - 100 95-100

16 1.428 28.56 28.56 71.44 75-90

12.5 1.545 30.90 59.46 40.54 60-75

10 1.323 26.46 85.92 14.08 25-55

4.75 0.668 13.36 99.28 0.72 0-10

Table-3.3 Properties of natural & recycled aggregate concretes:

PropertiesNA RCA

Bulk density (kg/m3) 1.513 1.375

Loose density (kg/m3) 1.438 1.313

Maximum size (mm) 12.5 12.5

Specific gravity 2.77 2.72

3.1.4 Polyethylene Glycol-600:

Polyethylene glycol is a condensation polymers of ethylene oxide and water with the general formula H(OCH2CH2)nOH, where n is the average number of repeating oxyethylene groups typically from 4 to about 180. 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. Specifications of PEG-600 are listed in table 3.4.

Table-3.4 Specifications of Polyethylene Glycol-600:

Polyethylene Glycol-600Molecular Weight 600

Appearance Clear liquidpH 5 – 7

Specific Gravity 1.126

3.1.5 Water:

Potable water was used in the experimental work for both mixing and curing purposes.

3.2 Casting Programme:

Casting programme consists of preparation of moulds as per IS 10086: 1982, preparation of materials, weighing of materials and casting of cubes, cylinders, beams.. Mixing, compacting and curing of concrete is done according to IS 516: 1959. The cubes which are intended for self curing are kept in indoor/shade at room temperature. Materials required for the mix is as shown below in table 3.5.

Table 3.6 Materials Required For Mix (B-R) (1:0.44:1.214:2.607) Peg600 (L)

S.No

Nomenclature

of Mix

No. of Cubes

+Cylinders

+Beams

Cement(Kg)

FA(Kg)

CA ( Kg)

Water(kg)

PEG(600)(ml)Natural

Recycled

1 NC-C-0 6+0+0 11.0 13.35 28.677 28.677 4.84 0

2 SC-C-1 6+1+1 20.0 24.28 52.140 52.140 7.92 177

3 SC-R-1 6+1+1 20.0 24.28 52.140 52.140 7.92 177

3.3 Testing Programme: Tests for Fresh Properties of Concrete:a. Slump Test: Slump test is the most commonly used method of measuring consistency of concrete which can be employed either in laboratory or at site of work. It does not measure all factors contributing to workability. However, it is used conveniently as a control test and gives an indication of the uniformity of concrete from batch to batch. b. Compacting Factor Test: The compacting factor test is designed primarily for use in the laboratory but it can also be used in the field. It is more precise and sensitive than the slump test and particularly useful for concrete mixes of very low workability as are normally used when concrete is to be compacted by vibration. Such dry concrete are insensitive to slump test. The compacting factor test values for both mixes are shown in table 3.7

Table 3.7 Compacting Factor and Slump for all mixes

MIXCOMPACTING

FACTORSLUMP

NC-C-0* 0.91 125mmSC-C-1* 0.90 123mmSC-R-1* 0.90 123mm

*0, 1 represents % of PEG used in particular mix.At the end of the required number of days of curing (28days) the specimens were taken out and tested on 3000KN Universal Testing Machine (UTM) as per IS 516.

3.4 Experimental Investigations:3.4.1 Compressive strength:

The cube specimens were tested on compression testing machine of capacity 3000KN. The bearing surface of machine was wiped off clean and looses other sand or other material removed from the surface of the specimen. The specimen was placed in machine in such a manner the load was applied to opposite sides of the cubes as casted that is, not top and bottom. The axis of the specimen was carefully aligned at the centre of loading frame. The load applied was increased continuously at a constant rate until the resistance of the specimen to the increasing load breaks down and no longer can be sustained. The maximum load applied on specimen was recorded. The compressive strengths of cubes for all the mix on an average are listed in table 4.1.

3.4.2 Split tensile strength: The cylinder specimens were tested on compression testing machine of capacity 3000KN.

The bearing surface of machine was wiped off clean and looses other sand or other material removed from the surface of the specimen. The axis of the specimen was carefully aligned at the centre of loading frame. The load applied was increased continuously at a constant rate until the resistance of the specimen to the increasing load breaks down and no longer can be sustained. The maximum load applied on specimen was recorded. The split tensile strengths of cylinders for all the mix are listed in table 4.1.

3.4.3 Flexure strength: The beam specimens were tested on universal testing machine. The bearing surface of

machine was wiped off clean and looses other sand or other material removed from the surface of the specimen. The axis of the specimen was carefully aligned at the centre of loading frame. The two point load applied was increased continuously at a constant rate until the resistance of the specimen to the increasing load breaks down and no longer can be sustained. The maximum load applied on specimen was recorded. The split tensile strengths of cylinders for all the mix are listed in table 4.1.

CHAPTER – 4

RESULTS AND DISCUSSION

The experimental program has been conducted as explained in chapter 3 on properties of self curing concrete using polyethylene glycol-600 and replacement of recycled aggregate for natural coarse aggregate.

4.1 Effect of PEG-600 on properties of concrete:

4.1.1 Compressive Strength:

a) MIX NC-C-0 and SC-C-1:

Table 4.1 shows the compressive strengths of the mix NC-C-0 and SC-C-1. From the figure 1, it shows that there is a decrease in strength for 1% PEG used specimens when compared to 0% PEG used specimens which were kept in wet curing. In the mix SC-C-1 the cube specimens with 1% PEG have shown difference in the strength which is comparable to the NC-C-0 cube specimens.

4.2 Effect of recycled coarse aggregate on properties of concrete:

4.2.1 Compressive Strength:

a) MIX SC-C-1 and SC-R-1:

Table 4.1 shows the compressive strengths of the mix SC-C-1 and SC-R-1 and from the figure 2, it is clear that the difference in strengths between the cube specimens with conventional coarse aggregate and recycled coarse aggregate after 7 days of self curing is comparable where as there is marginal difference between the cube specimens with conventional coarse aggregate and recycled coarse aggregate after 28 days of self curing.

4.2.2 Split Tensile Strength:

a) MIX SC-C-1 and SC-R-1:

Table 4.1 shows the split tensile strengths of the mix SC-C-1 and SC-R-1 and, it is clear that there is a marginal difference in tensile strengths between the cylinder specimens with conventional coarse aggregate and recycled coarse aggregate.

4.2.3 Flexure Strength:

a) MIX SC-C-1 and SC-R-1:

Table 4.1 shows the flexure strengths of the mix SC-C-1 and SC-R-1 and, the table shows that there is a marginal difference in tensile strengths between the cylinder specimens with conventional coarse aggregate and recycled coarse aggregate.

Table 4.1: Structural properties of all the concrete mix

MIXCOMPRESSIVE

STRENGTH(N/mm2) SPLIT TENSILE STRENGTH(kg/cm2)

FLEXURE STRENGTH(kg/cm2)7 days 28 days

NC-C-0 15.567 32.886 - -SC-C-1 14.67 27.84 26.88 149.94SC-R-1 13.33 23.11 21.22 110.25

Figure 1

7 280

5

10

15

20

25

30

35

15.567

32.886

14.67

27.84

Normal curingSelf curing

No. of days of curing

Com

pre

ssiv

e S

tren

gth

(N/m

m2)

Figure 2

7 280

5

10

15

20

25

30

14.67

27.84

13.33

23.11

SC-C-1SC-R-1

No. of days of curing

Com

pre

ssiv

e S

tren

gth

(N/m

m2)

CHAPTER – 5

CONCLUSIONS

For the specimen with the 0% and 1% self curing agent, the mix SC-C-1 showed compressive strength which is comparable with that of NC-C-0 after 7 days of curing. For the specimen with the 1% self curing agent, the mix SC-C-1 showed a significant difference in compressive strength after 28 days.

For the specimen with the 1% self curing agent, the mix with conventional coarse aggregate showed more split tensile strength than the mix with recycled coarse aggregate.

For the specimen with the 1% self curing agent, the mix with conventional coarse aggregate showed more flexure strength than the mix with recycled coarse aggregate.

REFERENCES

1. Roland Tak Yong Liang, Robert Keith Sun, “Compositions and Methods for Curing

Concrete”, Patent No. U.S. 6,468,344 B1 dated Oct. 22, 2002.

2. Wen-Chen Jau, “Self Curing Concrete”, Patent Application Publication No. U.S.

2008/0072799 A1 dated Mar. 27, 2008.

3. Ambily P.S, and Rajamane N P, “Self Curing Concrete An Introduction”, Structural

Engineering Research Centre, CSIR, Chennai.

4. Khalaf FM and DeVenny Alan S. “Recycling of demolished masonry rubble as coarse

aggregate in Concrete: review”. ASCE J Mater Civil Eng 2004:331–40.

5. Akash Raoa, Kumar N. Jha B, Sudhir Misra “Use of aggregates from recycled

construction and demolition waste in concrete”, Journal of Resources, Conservation and

Recycling (2006), Elsevier B.V.

6. D. S. R Murthy, S. Kanaka Durga “Performance of structural concrete with recycled

coarse aggregate”, Journal of Structural Engineering, SERC, Chennai