A Study on Rate of Strength Gain of Concrete Mix Prepared With Locally Available Composite Cement

A STUDY ON RATE OF STRENGTH GAIN OF CONCRETE MIX

PREPARED WITH LOCALLY AVAILABLE

COMPOSITE CEMENT

Submitted by

AL-Latiful Bari

Student N0.0404131

Kazi Ashfaq Hossain 0404003

Jahid Hasnain 0404005

Sanjib Kumar 0404170

Course: CE400 (Project and Thesis)

Thesis

Submitted in Partial Fulfillment of the Requirement for the Degree of

BACHELOR OF SCIENCE IN CIVIL ENGINEERING

Department of Civil Engineering

BANGLADESH UNIVERSITY OF

ENGINEERING AND TECHNOLOGY,DHAKA.

October, 2009.

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DECLARATION It is hereby that the work presented in this thesis has been carried out by the author under the supervisor of Dr. Khan Mahmud Amanat, Professor, Department of Civil Engineering, Bangladesh University of Engineering and Technology, Dhaka. This work has not been submitted elsewhere for any other purpose (except for publication).

(Al_Latiful Bari)

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_____________________________ACKNOWLEDGEMENT

The author expresses his profound gratitude and deep appreciation to his supervisor, Professor

Dr. Khan Mahmud Amanat, of Department of Civil Engineering, BUET, Dhaka, for his superior

guidance, encouragement, invaluable suggestion, untiring co-operation, amicable behavior, kind

attention and immense patience during the progress of the thesis. Without his prudential advice

and inspiring support, this project would not have been successful.

This author express his express his grateful thanks to his friends for their helpful activity during

the manufacturing of the concrete cylinders.

This author also expresses his gratitude to all the related staffs of the Concrete laboratory and

Transportation laboratory for their co-operation in the performing of the thesis.

And above all, I am thankful to Allah Almighty for His blessing accompanied by which I have

come so far.

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ABSTRACT In Bangladesh, locally available cements are composite cements. Pozzolana materials are commonly used in composite cement. Among those pozzolanic materials fly ash is well known to all. As industry Furnace, coal is used as fuel. Fly ash is the by-products of the burning coal from different industries. So, fly ash is primarily used as a pozzolanic material in composite cements of Bangladesh. A common complain arises that concrete made from composite cement does not achieve target strength within the design period. There is another argument found that the quality of cement productions are not properly controlled in the industry of Bangladesh. This thesis tries to find out the fact of strength gain of composite cement and focuses on the quality of composite cements that that are locally available. For this reason, this thesis presents the strength gaining properties of locally available composite cement at continuously curing and 14 days cured (non curing) type, then compare the compressive strength results with Ordinary Portland Cement.

In this thesis, compressive strength of concrete has been tested as per ASTM C39-96. For this project, four different brand of composite cement and one ordinary Portland cement have taken. The amount of different ingredients of concrete for the targeted compressive strength of 2500 psi, 4000 psi and 6000 psi are calculated by ACI mix design method. Using each brands of cement, concrete will be cast for three targeted design strengths. For each brand of cement and for particular target design strength, the compressive strength of concrete cylinders have tested at 3 days,7 days, 14 days, 28 days, 3 months and 6 months of the age of the concrete. For each particular age, 6 samples have tested (three for curing and three for non curing samples). Curing samples have kept under water continuously until they have been tested. Non curing samples will kept under water for 14 days and then these are left behind in air. The total 450 concrete cylinders have made to perform the test. From experimental observation, noncuring strength is higher than the curing strength, and then the curing strength is more. Due to presence of fly ash in composite cements, early strength is lower than the OPC strength. For this reason, target strength cannot achieve within design period 28days.also the difference between the OPC strength and composite cements strength are significantly varies. But, targeted strength achieved within 90 to 120 days. After 120 days, the strength of concrete is continued to attain with age on the concrete.

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TABLE OF CONTENTS

Declaration i

Acknowledgement ii

Abstract iii

Table of contents iv

List of Tables viii

List of Figures xi

Abbreviation xv

Notation xiv

Chapter 1. Introduction

1.1 General 1

1.2 Background and Present State of the problem 2

1.3 Research Significance 4

1.4 Objectives with specific aims and possible outcomes

1.4.1Objectives 4

1.4.2 Outcome 4

1.5 Outline of methodology 4

1.5.1 Physical properties of coarse and fine aggregate 5

1.5.2 Compressive strength of concrete 5

1.6 Method of Mix Design 5

Chapter 2 Literature Review

2.1 General 6

2.2 History of the concrete making materials 7

2.3 Elements of concrete 8

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2.4Cement as a prime concrete making element 8

2.4.1 History of modern cement 8

2. 4.2 Classification of cement 11

2.4.2.1 Indian Standard classification of cement 11

2.4.2.2 The European Standard for common Cements 12

2.4.2.3 ASTM standard classification 12

2.4.3 Ordinary Portland Cement 14

2.4.4 Composite cement 15

2.4.5 Portland Pozzolana Cement 16

2.4.5.1 Pozzolanic properties 16

2.4.5.2 Advantages of Pozzolanic cement 18

2.4.5.3 Classification of Pozzalana 18

2.5 Fly ash 19

2.5.1 Specification and classification of fly ash 19

2.5.2 Chemical composition of fly ash 21

2.6 Aggregates and its properties 21

2.6.1 Classification of aggregate 22

2.6.2 Source of aggregates 22

2.6.3 Important properties of aggregate 22

2.6.4 Testing of aggregates 23

2.7 Water 23

2.8 Chemical admixtures 24

2.9 Properties of fly ash concrete 25

2.9.1 Greater consolidation 25

2.9.2 Alkali-aggregate reaction 25

2.9.3 Strength of fly ash concrete 27

2.9.3.1 Water/cement ratio 27

2.9.3.2 Aggregate/cement ratio 28

2.9.3.3 Effects of size and properties of aggregate on strength 28

2.9.3.4 Gain of strength with age 31

2.9.3.5 Aggregate-cement bond strength 31

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2.10 Importance of use of fly ash in concrete 32

2.11 Remarks 33

Chapter 3 Properties aggregate, preparation and testing of concrete

3.1 General 34

Properties of coarse aggregate 34

3.2.1 Absorption capacity and specific gravity of coarse aggregates 34

3.2.2 Unit weight and void in coarse aggregate 35

3.2.3 Sieve analysis and gradation of coarse aggregate 35

3.3 Properties of fine aggregates 36

3.3.1 Unit weight of fine aggregate 36

3.3.2 Absorption capacity and specific Gravity of fine aggregate 37

3.3.3 Fineness modulus and gradation of fine aggregate 38

3.4 Choice on strength 39

3.5 Cement Brands 40

3.5.1 Proportions of ingredients 40

3.6 Testing age 40

3.7 Mould dimension 41

3.8 Number of specimens 41

3.9 Identity Marks for specimens 42

3.10 Preparation procedure 42

3.11 Compressive strength tests of concrete cylinders 54

Chapter 4 Strength of Concrete

4.1 General 57

4.2 Factors affecting concrete strength 57

4.3 Compressive Strength of concrete 57

4.4 Findings 58

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Chapter 5 Conclusion

5.1 General 87

5.2 Findings 87

5.3 Limitations 88

5.4 Recommendations 89

References 90

Appendix 1 93

Appendix 2 96

xv

ABBREVIATION

AASHTO American association of State Highway and Transportation Officials

ACI American Concrete Institute

ASTM American Society for Testing Materials

BS British Standard Specification

ICI Indian Concrete Institute

IS Indian Standard Specification

OPC Ordinary Portland Cement

PCA Pulverized Coal Ash

PPC Portland Pozzolana Cement

1 Introduction

CHAPTER 1

INTRODUCTION

1.1 GENERAL

Concrete is the most widely used construction material. Portland cement is the major ingredient of concrete. Though the raw materials needed for manufacture of cement are available in most parts of the world, many countries have severe shortage of cement, although their needs are vast. The search for suitable substitute for cement, either partially or fully, has thus become a challenge for planning the development of many of third world countries like us. At the same time, large-scale industrialization has led to newer environment problems related to disposal of industrial byproducts like fly ash. The thermal power stations existing in the world produce about 470 million tons fly ash worldwide every year. There are large numbers of other industries, which also use coal for firing their boilers, producing large amounts of fly ash, which are generally collected by mechanical collectors. Large stretches of land, which can otherwise be used for shelter, agriculture or some other productive purposes, are being wasted for disposal of fly ash; it is generally felt that ash collected from electrostatic precipitator of thermal power plants is very much suitable for use in production of high performance concrete.

According to ACI 116R, Cement and Concrete Technology, fly ash is the finely divided residue resulting from the combustion of ground or powdered coal which is transported from the firebox through the boiler by flue gases; known in UK as pulverized fuel ash (PEA). Fly ash possesses pozzolanic materials, primarily of volcanic or sedimentary origin, found in many parts of the world. About 2000 years ago the Romans mixed volcanic ash, called Pulvis Puteolanus (later change to Pozzolana) with lime to produce mortar and concrete (Vitruvius 1960, in translation). A pozzolana is a siliceous and aluminous material, which in itself possesses little or no cementitious value but will, in finely divided from and in the presence of moisture, chemically reacts with calcium hydroxide at ordinary temperatures to form compounds possessing cementitous properties (ACI 116R). Pozzolons, such as fly ash, are used as ingredients in Portland Cement Concrete.

Use of fly ash in concrete started in the U.S.A in the early 1930s R.E. Davis made the first comprehensive study in 1937 at the University of California (Davis, 1937). The Major breakthrough in using fly ash in concrete was Construction of Henry Horse Dam in 1984, utilizing 120000 metric Tons of fly ash. Davis and colleagues recognized in subsequent studies the relativity of the fly ash with calcium and alkali-hydroxides in Portland cement paste and otherwise the ability of the fly ash to react as a preventive measure against deleterious alkali-aggregate reactions. The U.S. Army

2 Introduction

corps of Engineers and other recognized the beneficial effects of the fly ash on the workability of the concrete and the advantageous reduction of peak temperatures in mass concrete. The beneficial aspects of fly ash were especially notable in the construction of large concrete dams (Mielenz, 1983). The oil crisis of the 1970s led to greater use of coal to fire electric power plants.

Fly ash containing higher levels of calcium oxide became available due to the use of coal and lignite containing calcium compound in their incombustible fractions. Most such coals in the United State are sub-bituminous and lignite. Concurrent with this increased availability of fly ash, extensive research in the USA, Canada and elsewhere has led to better understanding of the chemical reactions involved and improved the technology to economically use the large quantities of fly ash now available to the concrete industries (ACI, SP-79).

Fly ash used in concrete for reasons including economic, improvements and reduction in temperature rise in fresh concrete, workability and contribution to durability and strength in hardened concrete. Fly ash makes efficient use of the products of the hydration of Portland cement. Solution of calcium alkali-hydroxide, which exist in the pore structure of the cement paste and the heat, generated by hydration of Portland cement, an important factor in initiating the reaction of the fly ash.

When fly ash concrete is properly used, fly ash reaction products help fill in the spaces between hydrating cement particles in the cement paste fractions of the cement, thus lowering its permeability to water and aggregate chemicals (Monmohan and Merha, 1981). The slower reaction rate of many fly ashes is a real help in limiting the amount of early temperature rise in massive structures. Using fly ash in concrete saves energy by reducing the amount of Portland cement required to achieve the desired concrete properties.

1.2 BACKGROUND AND PRESENT STATE OF THE PROBLEM

Fly ashes are finely divided residue resulting from the combustion of ground or powdered coal. They are generally finer than cement and consist mainly of glassy-spherical particles as well as residues of hematite and magnetite, char, and some crystalline phases formed during cooling. Use of fly ash in concrete started in the United States in the early 1930's. The first comprehensive study was that described in 1937, by R. E. Davis at the University of California (Kohubu, 1968; Davis et al., 1937). The major breakthrough in using fly ash in concrete was the construction of Hungry Horse Dam in 1948, utilizing 120,000 metric tons of fly ash. This decision by the U.S. Bureau of Reclamation paved the way for using fly ash in concrete constructions.

The global cement industry contributes around 1.35 billion tons of the greenhouse gas emissions annually, or about 7% of the total man-made greenhouse gas emissions to the earths atmosphere (Malhotra, 2002; McCaffrey, 2002).Consumption of fly ash in

3 Introduction

cement production as either a particle replacement for, or an addition to Portland cement is an important strategy in making concrete more environmental friendly. Because its not only reduce CO2 emissions but also induce enhanced workability due to - spherical fly ash particles, - reduce bleeding and less water demand, - increase ultimate strength, - reduce permeability and chloride ion penetration, - lower heat of hydration, -greater resistance to sulfate attack, -greater resistance to alkali-aggregate reactivity and -reduced drying shrinkage (American Coal Ash Association, 1995). Even though the use of fly ash in concrete has increased in the last 20 years, less than 20% of the fly ash collected was used in the cement and concrete industries (Helmuth 1987).

One of the most important fields of application for fly ash is PCC pavement, where a large quantity of concrete is used and economy is an important factor in concrete pavement construction. FHWA has been encouraging the use of fly ash in concrete. When the price of fly ash concrete is equal to, or less than, the price of mixes with only portland cement, fly ash concretes are given preference if technically appropriate under FHWA guidelines (Adams 1988).

A critical drawback of the use of fly ash in concrete is that the rate of strength increase of fly ash concrete is slower but it is sustained for longer periods than the rate of the strength increase of Portland cement concrete(Hwang,2004; Chindaprasirt, Jaturapitakkul, 2005). That is why at early ages the compressive strength of Fly ash Cement will be lower than that of Portland cement, but by 28 days with correct mix design and applying adequate curing, the strength will be similar. To minimize the rising production cost, cement manufacturing companies of Bangladesh have been using fly ash in cement for the last few years. However instead of standard practice, they are using fly ash in cement with different proportion having different sources. These fly ash containing cement are available in the market named Composite Cement. The properties of these locally available composite cement vary among different cement manufacturing companies. Kaosar have made an extensive study on brick aggregate concrete with varying amount of fly ash content where fly ash are added directly at the time of mixing, various physical, chemical and strength properties of brick aggregate concrete have been studied. (Kaosar, 2006) This study gives a good picture of the effect of fly ash on brick aggregate concrete. However, since no locally available composite cement was used, characteristics of these cement are not directly reflected in the results. Moreover, stone aggregate is used in almost all major construction works in Bangladesh. Therefore, it is

4 Introduction

worthwhile to investigate the properties of stone aggregate concrete made with locally available composite cements.

1.3 RESEARCH SIGNIFICANCE

This research is conducted to evaluate the strength variation of concrete made from locally available composite cement (mixed with fly ash) with stone aggregate. Variation of strength is observed for continuously curing and fourteen days curing samples. All test is performed using locally available materials such as stone chips, sand (Sylhet Sand).

1.4 OBJECTIVES WITH SPECIFIC AIMS AND POSSIBLE OUTCOMES

1.4.1 Objectives

This thesis is to observer the strength variation of concrete. The objectives are as follows:

(a)To study the variation of compressive strength of concrete with time made with locally available composite cement containing fly ash.

(b)To compare compressive strength of concrete made from locally available composite cement with ordinary Type-1 Portland Cement.

(c)To study and compare the effect of continuously curing and only 14 days curing.

1.4.2 Outcome

Findings of the study will give a general scenario of the strength gain (with age) characteristics of locally composite cements which may be useful for construction planning of building. This study also gives an idea about the quality of locally available cements.

1.5 OUTLINE OF THE METHODOLOGY

For this project, four different brand of composite cement and one ordinary Portland cement have taken. The amount of different ingredients of concrete for the targeted compressive strength of 2500 psi, 4000 psi and 6000 psi are calculated by ACI mix design method. Using each brands of cement, concrete will be cast for three targeted design strengths. For each brand of cement and for particular target design strength, the compressive strength of concrete cylinders have tested at 3 days,7 days, 28 days, 3 months and 6 months of the age of the concrete. For each particular age, 6 samples have tested (three for curing and three for noncuring samples). Curing samples have kept under water continuously until they have been tested. Noncuring samples will kept under water for 14 days and then these are left behind in air. The total 450 concrete cylinders have made to perform the test.

5 Introduction

1.5.1 Physical properties of coarse and fine aggregate Different physical properties of both fine and coarse aggregate have been tested according to different ASTM codes.

Fineness modulus, unit weight and specific gravity of coarse aggregate have been performed according to ASTM C117-84, ASTM C136-84a, ASTM C29 /C 29 M-91a, ASTM C127-88 respectively.

Fineness modulus, unit weight and specific gravity of coarse aggregate have been performed according to ASTM C117-84, ASTM C136-84a, ASTM C29 /C 29 M-91a, ASTM C127-84 respectively.

1.5.2 Compressive strength of concrete

Compressive strength of concrete has been tested as per as ASTM C39-96. In this experiment, 450 concrete specimens have made according to design strength based on w/c ratio. For design strength 2500 psi, 4000 psi and 6000 psi w/c ratio is 0.68, 0.57 and 0.41 respectively are considered as mixing criteria. The dimensions of the concrete specimens, taken for this experiment are 4 inch in diameter and 8 inch in height.

Table 1.1 Different design strength and w/c ratio

Design Strength, psi w/c ratio

2500 0.68

4000 0.57

6000 0.41

1.6 METHOD OF MIX DESIGN

The mix design depends on the type of structure being built, how the concrete will be mixed and delivered, and how it will be placed to form this structure. Mix design is defined as the process of selecting suitable ingredients of concrete and determining their relative quantities with the purpose of producing an economical concrete, which has certain minimum properties, notably workability, strength and durability. Thus selection of better mix design method is vital to obtain desired strength of concrete. For this thesis, ACI method for mix design has been used, considering all design standards.

6 Literature Review

CHAPTER 2

LITERATURE REVIEW

2.1GENERAL

Concrete is a stone like construction material composed of carefully proportioned mixture of cement as well as other cementitious materials such as fly ash and slag cement, aggregate (generally a coarse aggregate such as gravel, limestone, or granite, plus a fine aggregate such as sand), water, and chemical admixtures. The word concrete comes from the Latin word "concretus" (meaning compact or condensed), the past participle of "concresco", from "com-" (together) and "Cresco" (to grow).

The bulk of the materials consists of fine aggregate and coarse aggregate. Cement and water interact chemically to bind the aggregate particles into solid mass. Adding water to the dry cement starts a chemical reaction (hydration).additional water, over and above thar needed for this chemical reactions, is necessary to give the mixture workability that enables it to fill the forms and surround the embedded reinforcing steel prior to hardening (Graynor,1978). While the mixture of cement, water, and rock is fluid, it can be poured into molds (called formwork) of arbitrary shape.

The component materials of concrete are mixed in varying proportions, according to the strength required and the function to be fulfilled. To obtain variety of properties the followings are required

Special type of cements ( such as High Early strength cements), Special aggregates (such as various lightweight or heavyweight aggregates ), Admixtures(such as plasticizers and air entraining agents), and Special curing methods( stream-curing)

These properties depend on a very substantial degree of the proportions of the mix, on the thoroughness with which the various constituents are intermixed, and on the conditions of humidity and temperature in which the mix is maintained from the moment it is placed in the formworks until it is fully hardened (Prince, 1951). To protect the concrete against the unintentional production of substandard concrete, a high degree of skillful control and supervision is necessary throughout the process, from the proportioning by weight of the individual components through mixing and placing, until the completion of curing. So, carefulness is a fundamental requirement to obtain better type of concrete.

7 Literature Review

2.2 HISTORY OF THE CONCRETE MAKING MATERIALS

The history of concrete making materials (such as cementing materials) is as old as the history of engineering construction. Some kind of cementing materials were used by Egyptians, Romans and Indians in their ancient constructions. It is believed that the early Egyptians mostly used cementing materials obtained by burning gypsum. Not much light has been thrown on cementing materials, used in the construction of the cities of Harappa and Mohanjadaro.

An analysis of mortar from the Great Pyramid showed that it contains 81.5 percent calcium sulphate (CaSO4), only 9.5 percent carbonate (Shetty, 2002). The early Greeks and Romans used cementing materials obtained from burning lime-stones. The remarkable hardness of the mortar used in the early Roman brick-work, some of which exists, is presenting sufficient evidence of the perception, which the art of cementing material had attained in ancient times. The superiority of Roman mortar has been attributed to thoroughness of mixing and long continued ramming.

The Greeks and Romans later became aware of the fact that certain volcanic ash and tuff, when mixed with lime and sand yielded mortar possessing superior strength and better durability in fresh and salt water. Roman builders used volcanic tuff found in Pozzuoli village near Mount Vesuvius in Italy. This Volcanic ash or tuff mostly siliceous in nature thus acquired the name Pozzolana. Later on, the name Pozzolana was applied to any other materials, natural and artificial, having nearly same composition as that of volcanic tuff or ash found at Pozzuoli. The Romans, in the absence of natural volcanic ash, used powdered tiles or pottery as pozzalana. In India, powdered brick named Surkhi has been used in mortar. The Indian of through mixing and long continued ramming of lime mortar with or without the addition of Surkhi yielded strong and impervious mortar which confirmed the secret of the superiority of Roman mortar (Shetty, 2002) . The cementing materials made by Romans using lime and natural or artificial pozzolana retained its position as the chief building material for all work, particularly, for hydraulic construction. Belidor, a principle authority in hydraulic construction, recommends an intimate mixture of tiles and stone chips, dried and then mixed with fresh slaked lime for making good concrete.

When we come more recent times, the most important advantages in the knowledge of cements, the forerunners the discoveries and manufacture of all modern cements is undoubtedly the investigations carried by John Smeaton. He concluded that lime-stones which contained considerable proportion of clayey matter, yield better lime possessing superior hydraulic properties. In spite of the success of Smeatons experiments, the use of hydraulic lime made little progress and then old practice of mixture of lime and pozzolana remained popular for a long period. In 1976, calcining nodules of argillaceous

8 Literature Review

lime-stone made hydraulic cement. In about 1800 the product, thus obtained was called Roman cement. This type of cement was in use till about 1850 after which this was outdated by Portland cement.

Recently, the use of recycled materials as concrete ingredients is gaining popularity because of increasingly stringent environmental legislation. The most conspicuous of these is fly ash, a by-product of coal-fired power plants. This has a significant impact by reducing the amount of quarrying and landfill space required, and, as it acts as a cement replacement, reduces the amount of cement required to produce a solid concrete. As cement production creates massive quantities of carbon dioxide, cement-replacement technology such as this will play an important role in future attempts to cut carbon dioxide emissions.

2.3 ELEMENTS OF CONCRETE

The main elements of concrete are cement, water, fine aggregate and coarse aggregate. To make concrete economical and obtain higher strength some admixtures are also used in concrete.

2.4 CEMENT AS A PRIME CONCRETE MAKING ELEMENT

A cement is a prime material having the power of adhesive and cohesive properties that makes it possible to blind together minerals fragments so as to produce a compact mass of masonry.

Cement is superior to any other binder under the following conditions:

1. For construction of structure in wet places and under water. 2. Where high strength is required. 3. Where mortar or plaster has to set quickly. 4. Where surface is needed to protect against weather and certain inorganic matter. 5. For decorative, ornamental and pointing works.

2.4.1 History of modern cement

Modern hydraulic cements began to be developed from the start of the Industrial Revolution (around 1800), driven by three main needs:

Hydraulic renders for finishing brick buildings in wet climates Hydraulic mortars for masonry construction of harbor works etc, in contact with

sea water. Development of strong concretes.

9 Literature Review

In Britain particularly, good quality building stone became ever more expensive during a period of rapid growth, and it became a common practice to construct prestige buildings from the new industrial bricks, and to finish them with a stucco to imitate stone. Hydraulic limes were favored for this, but the need for a fast set time encouraged the development of new cements. Most famous among these was Parker's "Roman cement" (Francis, 1977). This was developed by James Parker in the 1780s, and finally patented in 1796. It was, in fact, nothing like any material used by the Romans, but was a Natural cement" made by burning septaria - nodules that are found in certain clay deposits, and that contain both clay minerals and calcium carbonate. The burnt nodules were ground to a fine powder. This product, made into a mortar with sand, set in 515 minutes. The success of "Roman Cement" led other manufacturers to develop rival products by burning artificial mixtures of clay and chalk.

John Smeaton made an important contribution to the development of cements when he was planning the construction of the third Eddystone Lighthouse (1755-9) in the English Channel. He needed a hydraulic mortar that would set and develop some strength in the twelve hour period between successive high tides. He performed an exhaustive market research on the available hydraulic limes, visiting their production sites, and noted that the "hydraulicity" of the lime was directly related to the clay content of the limestone from which it was made. Smeaton was a civil engineer by profession, and took the idea no further. Apparently unaware of Smeaton's work, the same principle was identified by Louis Vicat in the first decade of the nineteenth century. Vicat went on to devise a method of combining chalk and clay into an intimate mixture, and, burning this, producedartificial cement" in 1817. James Frost,( Francis, 1977) working in Britain, produced what he called "British cement" in a similar manner around the same time, but did not obtain a patent until 1822. In 1824, Joseph Aspdin patented a similar material, which he called Portland cement, because the render made from it was in color similar to the prestigious Portland stone.

All the above products could not compete with lime/pozzolan concretes because of fast-setting (giving insufficient time for placement) and low early strengths (requiring a delay of many weeks before formwork could be removed). Hydraulic limes, "natural" cements and "artificial" cements all rely upon their belite content for strength development. Belite develops strength slowly. Because they were burned at temperatures below 1250 C, they contained no alite, which is responsible for early strength in modern cements. The first cement to consistently contain alite was made by Joseph Aspdin's son William in the early 1840s. This was what we call today "modern" Portland cement. Because of the air of mystery with which William Aspdin surrounded his product, others have claimed precedence in this invention, but recent analysis of both his concrete and raw cement have shown that William Aspdin's product made at Northfleet, Kent was a true alite-based cement. However, Aspdin's methods were "rule-of-thumb": Vicat is responsible for

10 Literature Review

establishing the chemical basis of these cements, and Johnson established the importance of sintering the mix in the kiln.

William Aspdin's innovation was counter-intuitive for manufacturers of "artificial cements", because they required more lime in the mix (a problem for his father), because they required a much higher kiln temperature (and therefore more fuel) and because the resulting clinker was very hard and rapidly wore down the millstones which were the only available grinding technology of the time. Manufacturing costs were therefore considerably higher, but the product set reasonably slowly and developed strength quickly, thus opening up a market for use in concrete. The use of concrete in construction grew rapidly from 1850 onwards, and was soon the dominant use for cements. Thus Portland cement began its predominant role.

In India, Portland cement was first manufactured in 1904 near madras, by the South India Industrial Ltd. But this venture was failed. Between 1912 and 1913, the Indian cement co. ltd., was established at Porbander (Gujrat) and by 1914 this company was able to deliver about 1000 tons of Portland cement. By 1918 three factories were established. Together they were able to produce about 85000 tons of cement per year. During the first Five- Year plan (1951-11956) cement production in India rose was 2.69 million tons to 4.60 tons. By 1969 the total production of cement in India was 13.2 million tons and India was then occupying the 9th place in the world, with the USSR producing 89.6 million tons and the USA producing 70.5 million tons (CRI,1970).

Prior of the manufacture of Portland cement in India, it was important from UK and only a few reinforced concrete structures were built with improved cement. A three stored structure built as Byculla, Bombay is one of the oldest RCC structures using Portland cement in India. A concrete masonry building on mount road at Madras (1903), the har-ki-pahari bridge in Haridwar (1908) and the Cotton Depot Bombay, then one of the largest of its kind in the world (1922) are some of the oldest concrete structure in India (Indian Information, 1978). The early scientific study of cement did not reveal much about the chemical reactions that take place at the time of burning. A deeper study of the fact is , the clayey constituents of lime-stone are responsible for the hydraulic properties in lime (as established by John Smeaton) was not taken foe further research. It may be mentioned that among the earlier cement technologies, Vicat, Le Chatelied and Michael were the pioneers in the theoretical and practical field.

Systematic work on the composition and chemical reaction of Portland cement first began in the United States. The study on setting was undertaken by the bureau of standard and since 1926, much work on the study of Portland cement was also conducted by the Portland cement association, U.K. By this time, the manufacture and use of Portland cement had spread to many countries. Scientific work on cement and fundamental


contributions to the chemistry of Portland cement were carried out in Germany, Italy, France, Sweden, Canada and USSR, in addition to Britain and USA. In Great Britain with the establishment of Building Research station in 1921 a systematic research programmers was undertaken and many major contributions have been made (documentation bibliographic, 1941).

2.4. 2 Classification of cement

All developed countries have their own national standards for cements. These standards define the permitted cement composition and set performance requirements for properties such as setting time and development of compressive strength. They also describe the test procedures to be used to determine cement composition and cement properties. Although it is now rather out of date, particularly in relation to the standards in place in European countries, the publication by Cembureau, (1991) provides a useful review of cement types produced around the world.

In the past, national cement standards in many countries have been strongly influenced by those developed in the UK and published by the British Standards Institution (BSI) and by those developed in the USA and published by the American Society for Testing and Materials (ASTM). In 1991 The BSI published revised cement standards, which were closely aligned with the draft European Standard for Common Cements. This European Standard (EN 197-1) was adopted in 2000 by the following European countries: Austria, Belgium, Denmark, Finland, France, Germany, Greece, Iceland, Ireland, Italy, Luxembourg, Norway, Portugal, Spain, Sweden, Switzerland and the United Kingdom. The objective of this standard (in common with standards for other materials) is to remove barriers to trade. In order to meet this objective, existing national standards in the above countries were withdrawn in 2002. It can be expected that this European standard and the supporting standards for test methods (EN 196) and for assessment of conformity (EN 197-2) will have a strong influence on national (or regional) cement standards in the future.

2.4.2.1 Indian Standard classification of cement, 1989 (IS)

1. Ordinary Portland Cement. 2. Rapid Hardening Cement. 3. Extra Rapid Hardening Cement. 4. Sulphate Resisting Cement. 5. Blast Furnace Cement. 6. Quick Setting cement. 7. Super-Sulphate Cement. 8. Low Heat Cement.


9. Pozzolana Cement. 10. Air-entrained Cement. 11. Colored Cement. 12. Hydro Phobic Cement. 13. Masonry Cerement. 14. Expansive Cement. 15. Oil-well Cement. 16. Redi-set Cement. 17. High Aluminum Cement. 18. High Strength Cement. 19. Acid-Rresisting Cement.

2.4.2.2 The European Standard for Common Cements (EN 197-1) Europeans countries formed a common cement classification group which is called CEN (European Committee for Standardization). CEN member countries voted to adopt EN 197-1 in 2000. In 2002 conflicting British Standards (such as BS 12) will be withdrawn. The British Standard for sulfate-resisting cement, BS 4027, will continue until such time as agreement is reached on a European Standard for sulfate-resisting cement. Table 2.1 summarizes the range of cement compositions permitted by EN 197-1. While these are common cements they are not all available in all CEN member countries. For example, Portland burnt shale cement requires a particular shale type, which is only found in southern Germany.

2.4.2.3 ASTM standard Classification

According to American Society for Testing Materials (ASTM), cement are classified and they are classified as Type , type II, Type III, Type IV and type VI.

Type I

This type of Portland cement is known as common or general purpose cement. It is commonly used for general construction especially when making precast and precast-prestressed concrete that is not to be in contact with soils or ground water. The typical compound compositions of this type are: 55% (C3S), 19% (C2S), 10% (C3A), 7% (C4AF), 2.8% MgO, 2.9% (SO3), 1.0% Ignition loss, and 1.0% free CaO.

Type II

This type of cement is intended to use for moderate sulfate resistance with or without oderate heat of hydration. This type of cement costs about the same as Type I. Its typical


compound composition is:51% (C3S), 24% (C2S), 6% (C3A), 11% (C4AF), 2.9% MgO, 2.5% (SO3), 0.8% Ignition loss, and 1.0% free CaO.

Table 2.1 Cement types and compositions permitted by EN 197-1

Type III This type has relatively high early strength. This type of cement is commonly referred as rapid hardening cement. Its typical compound composition is: 57% (C3S), 19% (C2S), 10% (C3A), 7% (C4AF), 3.0% MgO, 3.1% (SO3), 0.9% Ignition loss, and 1.3% free CaO.

This cement is similar to Type I, but ground finer. Its 3 days and 7 days strength gain is higher than the Type I and Type II cement. The only downside is that the six month strength of type III is the same or slightly less than that of types I and II.


Type IV

This type of Portland cement is generally known for its low heat of hydration. Its typical compound composition is: 28% (C3S), 49% (C2S), 4% (C3A), 12% (C4AF), 1.8% MgO, 1.9% (SO3), 0.9% Ignition loss, and 0.8% free CaO.

The percentages of (C2S) and (C4AF) are relatively high and (C3S) and (C3A) are relatively low. A limitation on this type is that the maximum percentage of (C3A) is seven, and the maximum percentage of (C3S) is thirty-five. This causes the heat given off by the hydration reaction to develop at a slower rate. This type of cement has not been made for many years, because Portland-pozzolan cements and ground granulated blast furnace slag addition offer a cheaper and more reliable alternative.

Type V

This cement is used where sulfate resistance is important. Its typical compound composition is:

38% (C3S), 43% (C2S), 4% (C3A), 9% (C4AF), 1.9% MgO, 1.8% (SO3), 0.9% Ignition loss, and 0.8% free CaO.

This cement has a very low (C3A) composition which accounts for its high sulfate resistance.

It is noted that Type IV, Type V Portland cement has mainly been supplanted by the use of ordinary cement with added ground granulated blast furnace slag or tertiary blended cements containing slag and fly ash.

Types Ia, IIa, and IIIa have the same composition as types I, II, and III. The only difference is that in Ia, IIa, and IIIa an air-entraining agent is ground into the mix. The air-entrainment must meet the minimum and maximum optional specification found in the ASTM manual.

2.4.3 Ordinary Portland cement

This is the most common cement used in general concrete construction when there is no exposure to sulphate in the soil or in groundwater. The origin of the name of Portland cement was usually attributed to Joseph Aspdin, a brick mason in England. The common physical properties of OPC are as follow:

Finely powdered substance Gray to brownish gray


Composed of crystalline minerals (CaO) Particle size ranges from 0.5 micron to 80 micron in diameter specific gravity ranges from 3.12 to 3.16

The oxide composition and principle component in Portland cement are given in table 2.2 and 2.3(ASTM C150-98)

Table 2.2 Oxide Composition of Ordinary Portland cement (ASTM C150-98)

Oxide Composition CCN Mass% Calcium oxide, CaO C 61-67%

Silicon oxide, SiO2 S 19-23% Aluminium oxide, Al2O3

A 2.5-6%

Ferric oxide, Fe2O3 F 0-6% Sulfate 1.5-4.5%

Table 2.3 Principle components of OPC (ASTM C150-98)

Name of component Symbol CCN % Mass

Tricalcium silicate (CaO)3.SiO2 C3S 45-75%

Dicalcium silicate (CaO)2.SiO2 C2S 7-32%

Tricalcium aluminate (CaO)3.Al2O3 C3A 0-13%

Tetracalcium aluminoferrite (CaO)4.Al2O3.Fe2O3 C4AF 0-18%

Gypsum CaSO4 2 H2O 2-10% 2.4.4 Composite Cement: Composite cements are cements in which a proportion of the Portland cement clinker is replaced by industrial by-products, such as granulated blastfurnace slag (gbs) and power station fly ash (also known as pulverized-fuel ash or pfa), certain types of volcanic material (natural pozzolanas) or limestone. The gbs, fly ash and natural pozzolanas react with the hydration products of the Portland cement, producing additional hydrates, which make a positive contribution to concrete strength development and durability. Table 2.4 shows the characteristics of constituents of composite cements (Newman & Choo, 2003).


In contrast, finely ground limestone, while not hydraulically active, modifies the hydration of the clinker minerals. It is introduced to assist in the control of cement strength development and workability characteristics. In some European countries, notably Belgium, France, the Netherlands and Spain, the quantity of composite cements produced considerably exceeds that of pure Portland cement. According to statistics supplied by the association of European cement manufacturers (Cembureau) the average proportion of pure Portland cement delivered in European Union countries was 38% in 1999 the remainder being composite cements. The proportion of composite cements in the UK is at present very much lower, and the UK also differs from most European countries in that the addition of ground granulated blastfurnace slag (ggbs) and fly ash at the concrete mixer is well established. More recently (2002), although there are regional variations, most of the ready-mixed concrete produced in the UK contains either ggbs (at ~50% level) or fly ash (at ~30% level). The partial replacement of energy-intensive clinker by an industrial by-product or a naturally occurring material not only has environmental advantages but also has the potential to produce concrete with improved properties including long-term durability.

2.4.5 Portland pozzolana cement

The history of Pozzalana materials goes back to Roman time. It was recognised long ago, those suitable pozzolana used in appropriate amount modify certain properties of fresh and hardened morters and concrete (Chatterjee, 1999). Ancient Greeks and Romans used finely siliceous materials which when mixed with lime produced strong cementing materials having hydraulin properties and such cementing materials was employed in the construction of aquaducts, arches, bridges etc. One such materials was consolidated volcanic tuff or fly ash found in Pozzuoli (Italy) near Vesuvius. This came to be designed as Pozzalana, a general term covering similar materials of volcanic origin found in other deposits in Italy, France and Spain. Later, the term pozzalana was employed throughout Europe to designate any materials irrespective of its origin, which possessed similar properties (Efrent, 1973).

2.4.5.1 Pozzolanic properties

Pozzolana as a siliceous or silicious and aluminous materials which itself possesses little or no cementatious value, but will, in finely divided form and in the presence of moisture, chemically react with calcium hydroxide at ordinary temperature to form compounds possessing cementitious properties (ASTM, C 618, 1998).


Table 2.4 The characteristics of the constituents of composite cements (Newman & Choo, 2003). Constituents

Siliceous fly ash(bituminous)

Natural pozzolana

Granulatedblastfurnace slag

Limestone

Reaction type

Pozzolanic

Pozzolanic

Latently hydraulic

Hydration modifier

Brief description

Partly fused ash from the combustion of pulverized coal in power stations

Material of volcanic origin such as ash

Produced by rapid quenching of molten blastfurnace slag

Calcium carbonate of specified purity

Typical composition

Range

Range

Range

Typical

SiO2 3864 6075 3037 3 Al2O3 2036 1020 917 0.5 Fe2O3 418 110 0.22 0.5 CaO 110 15 3445 51 MgO 0.52 0.22 413 2 S _ _ 0.52 _ SO3 0.32.5


development will according be slow. The reaction involves the consumption of Ca(OH)2. The reduction of the Ca(OH)2 improves the durability of cement paste by making the paste dense and impervious.

2.4.5.2 Advantage of Pozzolanic Cement

It has been amply that the best pozzolanas in optimum proportions mixed with Portland cement improve many qualities of concrete (Devis,1950) such as:

a. Lower heat of hydration and thermal shrinkage. b. Increase the water tightness. c. Reduced the alkali aggregate-reaction. d. Improved resistance to attack by Sulphate soils and sea water. e. Improve extensibility. f. Lower susceptibility to dissolution and leaching. g. Improves workability. h. Lower cost.

In addition to these advantages, contrary to the general opinion, good pozzolanas will not unduly increase water requirement or drying shrinkage.

2.4.5.3Classification of Pozzolana

There are mainly two groups of pozzolana materials (ASTM C 618, 1998) : A. Natural pozzolana B. Artificial pozzolana

A. Natural pozzolana(ASTM C 618, 1998):

Pozzolanas are present on the earths surface such as diatomaceous earth, volcanic ash, opaline shale, pumicite, and tuff. These materials require further processing such as calcining, grinding, drying,etc. The Aegean island of Santorini has natural deposits of volcanic ash (Santorin Earth). In the United States, volcanic tuffs and pumicites, diatomaceous earth, and opaline shales are found principally west ot the Mississippi Rriver Okalahama, Navada, Arizona and California. Natural pozzolana have been used in dams and bridges to lower the heat of hydration and increase resistance of concrete to sulphate attack and control the alkali-silica reaction. Usually the pozzolanic deposit must be in the vicinity of the project to support mining and processing costs.

B. Artificial pozzolana (ASTM C 618, 1998)

Fly ash is an artificial pozzolana produced when pulverized coal is burned in electric


Power plants. The glassy (amorphour) spherical particulates are the active pozzolanic portion of fly ash. Fly ash is 66%-68% glass. Class F fly ash (ASTM C 618, 1998) readily reacts with lime (produced when Portland cement hydrates) and alkalies to form cementatious compounds. Class C fly ash also may exhibit hydraulic (self-cementing) properties. Hungry horse, Canyon Ferry, Palisades, Yellowtail dams all contains Portland cement- fly ash concrete.

2.5 FLY ASH

Fly ashes are finely divided residue resulting from the combustion of ground or powdered coal. They are generally finer than cement and consist mainly of glassy-spherical particles as well as residues of hematite and magnetite, char, and some crystalline phases formed during cooling. Use of fly ash in concrete started in the United States in the early 1930's. The first comprehensive study was that described in 1937, by R. E. Davis at the University of California (Kohubu, 1968; Davis et al., 1937). The major breakthrough in using fly ash in concrete was the construction of Hungry Horse Dam in 1948, utilizing 120,000 metric tons of fly ash. This decision by the U.S. Bureau of Reclamation paved the way for using fly ash in concrete constructions.

In addition to economic and ecological benefits, the use of fly ash in concrete improves its workability, reduces segregation, bleeding, heat evolution and permeability, inhibits alkali-aggregate reaction, and enhances sulfate resistance. Even though the use of fly ash in concrete has increased in the last 20 years, less than 20% of the fly ash collected was used in the cement and concrete industries (Helmuth 1987).

One of the most important fields of application for fly ash is PCC pavement, where a large quantity of concrete is used and economy is an important factor in concrete pavement construction. FHWA has been encouraging the use of fly ash in concrete. When the price of fly ash concrete is equal to, or less than, the price of mixes with only portland cement, fly ash concretes are given preference if technically appropriate under FHWA guidelines (Adams 1988).

2.5.1 Specification and Classification of Fly ash (ASTM C618, 1998)

ASTM broadll classified fly ash into two classes. They are Class F and class C fly ash.

Class F:

The burning of harder, older anthracite and bituminous coal typically produces Class F fly ash. This fly ash is pozzolanic in nature, and contains less than 10% lime (CaO). Possessing pozzolanic properties, the glassy silica and alumina of Class F fly ash requires


a cementing agent, such as Portland cement, quicklime, or hydrated lime, with the presence of water in order to react and produce cementitious compounds. Alternatively, the addition of a chemical activator such as sodium silicate (water glass) to a Class F ash can lead to the formation of a geopolymer.

Class C:

Fly ash produced from the burning of younger lignite or sub bituminous coal, in addition to having pozzolanic properties, also has some self-cementing properties. In the presence of water, Class C fly ash will harden and gain strength over time. Class C fly ash generally contains more than 20% lime (CaO). Unlike Class F, self-cementing Class C fly ash does not require an activator. Alkali and sulfate (SO4) contents are generally higher in Class C fly ashes.

Fly ash Bricks:

At least one US manufacturer has announced a fly ash brick containing up to 50 percent Class C fly ash. Testing shows the bricks meet or exceed the performance standards listed in ASTM C 216 for conventional clay brick; it is also within the allowable shrinkage limits for concrete brick in ASTM C 55, Standard Specification for Concrete Building Brick. It is estimated that the production method used in fly ash bricks will reduce the embodied energy of masonry construction by up to 90%. Bricks and pavers are expected to be available in commercial quantities before the end of 2009.

The most-often-used specifications for fly ash are ASTM C 618 and AASHTO M 295. While some differences exist, these two specifications are essentially equivalent. Some state transportation agencies have specifications that differ from the standards (Admixtures and Ground Slag 1990). The general classification of fly ash by the type of coal burned does not adequately define the type of behavior to be expected when the materials are used in concrete.

Whether both types of fly ash impart a wide range of qualities to many types of concretes, there are also wide differences in characteristics within each class. Despite the reference in ASTM C 618 to the classes of coal from which Class F and Class C fly ashes are derived, there was no requirement that a given class of fly ash must come from a specific type of coal. For example, Class F ash can be produced from coals that are not bituminous. and bituminous coals can produce ash that is not Class F (Halstead 1986). It should be noted that current standards contain numerous physical and chemical requirements that do not serve a useful purpose. Whereas some requirements are needed for ensuring batch-to-batch uniformity, many are unnecessary (RILEM 1988).


Concrete manufactures, engineers, developers, architects and contractors all have an interest in specifying or using fly ash on a routine bases to improve the quality of their project and to increase their cost effectiveness.

2.5.2 Chemical composition of fly ash (ASTM C 618, 1998)

1. The chemical compositions of fly ash and ordinary Portland cement are very similar to each other. Fly ash is amorphous (glassy) due to rapid cooling whether Portland cement is crystalline due to slower cooling.

Table 2.7 Chemical composition of Fly ash (ASTM C 618, 1998)

Component Bituminous Subbituminous Lignite

SiO2 (%) 20-60 40-60 15-45

Al2O3 (%) 5-35 20-30 20-25

Fe2O3 (%) 10-40 4-10 4-15

CaO (%) 1-12 5-30 15-40 LOI (%) (Loss of ignition)

0-15 0-3 0-5

2. The major difference between fly ash and Portland cement is the relative quantity of each of the different compounds. Portland cement is rich in lime (CaO) while fly ash is in low here. Fly ash is high in reactive silicates while Portland cement has smaller amount.

Fly ash material solidifies while suspended in the exhaust gases and is collected by electrostatic precipitators or filter bags. Since the particles solidify while suspended in the exhaust gases, fly ash particles are generally spherical in shape and range in size from 0.5 m to 100 m. They consist mostly of silicon dioxide (SiO2), which is present in two forms: amorphous, which is rounded and smooth, and crystalline, which is sharp, pointed and hazardous; aluminium oxide (Al2O3) and iron oxide (Fe2O3). Fly ashes are generally highly heterogeneous, consisting of a mixture of glassy particles with various identifiable crystalline phases such as quartz, mullite, and various iron oxides.

2.6 AGGREGATE AND ITS PROPERTIES

Aggregate are important constituents in concrete. Fine and coarse aggregates make up the bulk of a concrete mixture. Sand, natural gravel and crushed stone are mainly used for this purpose. They reduce shrinkage of concrete. Earlier aggregates were considered as chemically inert materials but now it has been recognized that some of the aggregates are


chemically activate. Certain aggregate exhibits chemical bond at the interface of aggregate and paste. The mere fact is that the aggregates occupy 70-80%of the volume of the concrete, their impact on various characteristics and properties of the concrete is certainly considerable (Shetty, 2002). To know more about the concrete, it is very essential that one should know more about the aggregates which constitute major volume in concrete. Without the study of aggregate in the depth range, the study of concrete is incomplete. Cement is the only factory made standard compound. Other ingredient, namely, water and aggregates are natural materials and can vary ant extent in many of the physical and chemical properties. The depth and range of studies that are required to be made in respect of aggregates to understand their widely varying effects and influences on the properties of concrete cannot be underrated.

2.6.1 Classification of aggregate (ASTM C289, 1981)

Aggregate can be classified as

i. Normal weight aggregate ii. Light weight aggregate

iii. Heavy weight aggregate

Normal weight aggregate can be further classified as natural aggregates and artificial aggregates.

i. Natural aggregate: Aggregates that are naturally found. Sand, gravel, crusher rock such as granite, quantize, basalt, sandstone are the example of natural aggregate.

ii. Artificial aggregate: Broken brick chips, Air-cooled Slag, Sintered fly ash, Bloated clay are the example of artificial aggregate.

2.6.2 Source of aggregates

Almost all natural aggregate materials originated from bed rock. The main sources of aggregates are:

a. Igneous Rocks b. Sedimentary Rocks c. Metamorphic Rocks

2.6.3 Important properties of aggregate

The following properties should be carefully studied to obtain the better quality of aggregate both for coarse and fine aggregate for concrete (Shetty, 1993).

Size Shape


Texture Strength Aggregate impact value Aggregate abrasion value Los Angeles test Bulk density Specific gravity Absorption Moisture content Porosity Bulking of sand Organic impurities Thermal properties Fineness Modulus

2.6.4 Testing of aggregates

The following tests are usually conducted in the laboratory to control the quality of aggregate and also to get satisfactory performance--

a. Sieve analysis (to obtain Fineness Modulus and Gradation) b. Test to determine elongation index c. Test to determine specific gravity d. Test to determine bulk density e. Test to determine aggregate absorption value

2.7 WATER

Water is an important ingredient of concrete as it actively participates in the chemical reaction with cement. As this helps to form the strength giving to cement gel, the equality and quantity of water is required to de looked with great care.

Combining water with a cementitious material forms a cement paste by the process of hydration. The cement paste glues the aggregate together, fills voids within it, and allows it to flow more easily.

Less water in the cement paste will yield a stronger, more durable concrete; more water will give an easier-flowing concrete with a higher slump.

Impure water used to make concrete can cause problems when setting or in causing premature failure of the structure.


Hydration involves many different reactions, often occurring at the same time. As the reactions proceed, the products of the cement hydration process gradually bond together the individual sand and gravel particles, and other components of the concrete, to form a solid mass.(Shetty,1993)

Reaction:

Cement chemist notation: C3S + H2O CSH(gel) + CaOH

Standard notation: Ca3SiO5 + H2O (CaO)(SiO2)(H2O)(gel) + Ca(OH)2

Balanced: 2Ca3SiO5 + 7H2O 3(CaO)2(SiO2)4(H2O)(gel) + 3Ca(OH)2

2.8 CHEMICAL ADMIXTURES

Chemical admixtures are materials in the form of powder or fluids that are added to the concrete to give it certain characteristics not obtainable with plain concrete mixes. In normal use, admixture dosages are less than 5% by mass of cement, and are added to the concrete at the time of batching/mixing. The most common types of admixtures are:

Accelerators speed up the hydration (hardening) of the concrete. Typical materials used are CaCl2 and NaCl.

Retarders slow the hydration of concrete, and are used in large or difficult pours where partial setting before the pour is complete is undesirable. A typical retarder is table sugar, or sucrose (C12H22O11).

Air entrainments add and distribute tiny air bubbles in the concrete, which will reduce damage during freeze-thaw cycles thereby increasing the concrete's durability. However, entrained air is a trade-off with strength, as each 1% of air may result in 5% decrease in compressive strength.

Plasticizers (water-reducing admixtures) increase the workability of plastic or "fresh" concrete, allowing it be placed more easily, with less consolidating effort. Superplasticizers (high-range water-reducing admixtures) are a class of plasticizers which have fewer deleterious effects when used to significantly increase workability. Alternatively, plasticizers can be used to reduce the water content of a concrete (and have been called water reducers due to this application) while maintaining workability. This improves its strength and durability characteristics.

Pigments can be used to change the color of concrete, for aesthetics. Corrosion inhibitors are used to minimize the corrosion of steel and steel bars in

concrete. Bonding agents are used to create a bond between old and new concrete.


Pumping aids improve pumpability, thicken the paste, and reduce dewatering the tendency for the water to separate out of the paste.

2.9 PROPERTIES OF FLY ASH CONCRETE

Fly ash concrete is the best known, and one of the most commonly used pozzolans in the world. Fly ash greatly influences the properties of concrete described below:

2.9.1 Greater consolidation

Fly ash concrete is actually more workable than plane cement concrete (Highway Research Board, Bulletin, 1960) at equivalent slump (fig: 2.1). the VEBE test measure the time and energy necessary for the consolidation of concrete under vibration.

Figure: 2.1 Typical Vebe time Vs Slump ( Highway Research Board, Bulletin, 1960).

Fly ash contributes great benefits to concrete in areas of hot weather by lowering the temperature. It can be used in high volume concrete mix where heat generating rate is high to reduce temperature and thus can minimize the internal crack of concrete. Scientists and engineers suggest using fly ash in heavy constructions to achieve greater strength and durability because fly ash gives dense, void free concrete.

2.9.2 Alkali-aggregate reaction

The unique properties of fly ash not only beneficial but also essential in some cases for The decreasing reaction between cement and aggregate during the concreting process (Figure 2.2) (Elferr, 1973).


Figure: 2. 2 Effects of fly ash on the expansion of concrete (Elferr, 1973).

Under certain condition and in certain areas, reactive silica in aggregate will react with soluble alkalis from any available source causing excessive and deleterious expansion. Volume changes will occur over a period of time, which causes the concrete to spall at the surface. In addition to the resulting surface ruptures, interior stresses may occur which cause cracking seriously impair structural integrity of the concrete.

The use of low alkali cement (


resistance to alkali/silica reaction. this purpose, in Jamuna Bridge, pozzalana cements have been used.

In addition to the use of fly pozzolanic material, it is recommended that low-alkali cement (less than 0.6%) and acceptable aggregates be used in order to prevent alkali/silica reactions.

2.9.3 Strength of fly ash concrete

Strength gain contributer by Portland cement occurs very rapidly at the early stage vp to seven days, after which it slows markedly. Strength devdlopment contributed by fly ash occurs through chemical contributions of the reactive fly ash glass with calcium hydroxide generated by hydration of the Portland cement. This process is callen pozzolanic activity. A fly ash concret, designed for equivalent performance to conventional cpncrete at normal ages, will generally gain strength slowly at early age. Later, the rate of strength gains of fly ash concrete is almost equal to the strength of conventional concrete.

For given cement and acceptable aggregates, the strength that may be developed by workable, properly mixing of cement, aggregate and water (under the same mixing, curing and testing conditions ) is influenced by

i. Ratio of cement mixing water; ii. Ratio of cement to aggregate;

iii. Grading, surface texture, shape, strength and stiffness of aggregate particles ; iv. Maximum size of aggregate; v. Aggregate-cement bonding;

vi. Others etc.

2.9.3.1 Water / cement ratio:

Strength of concrete primarily depends upon the strength of cement paste. It has been shown that the strength of cement paste depends upon the dilute of paste or in other words, the strength of paste increases with cement content and decreases with air and water content. In 1918, Abrams presented this classic law in the form:

S=

Where, S= strength, A =water/ cement ratio by volume and for 28 days results the constants A and B are 14000 lbs/sq. in. and 7 respectively.

Abrams water/cement ratio law states that the strength of concrete is only dependent upon water/cement ratio provided the mix workable.


Honestly speaking, it was Faret, who formulated in as early as 1897, a general rule defining the strength of the concrete paste and concrete in terms of volume fractions of the constituents by the equation,

S=K( ++

)

Where, S= strength of concrete, e and a= volume of cement, water and air respectively and K= a constant.

In this expression the volume of air is also included because it is not only the water/cement ratio but also the degree of compaction, which indirectly means the volume of air filled voids in the concrete is taken into account in estimating the strength of concrete. The relation between the water/cement and strength of concrete is shown in figure 2. 3. It can be seen that lower water/cement ratio could be used when the concrete is vibrated to achieve higher strength, whether comparatively higher water/cement ratio is required when concrete are hand-compacted. In both cases when the water/ cement ratio is below the practical limit the strength of the concrete falls rapidly due to introduction of air voids.

Sometimes it is difficult to interpolate the intermediate value. From geometry it can be deduced that if a graph is drawn between the strength and the cement/water ratio and approximately linear relationship will be obtained. This linear relationship is more convenient to use than water/cement ratio curve for interpolation. Figure 2.4 shows the relationship between compressive strength and cement/water ratio.

Instead of relating the strength to water/cement ratio, the strength can be more correctly related to the solid products of hydration of cement to the space available for the formation of the product.

2.9.3.2 Aggregate/cement ratio

It has been found that, for a constant water/cement ratio, a leaner mix leads to a higher strength. The influence of aggregate/cement ratio on strength of concrete is shown is figure 2.5. the main expansion of this influences lies in the total volume of voids in the concrete. If the paste represents a smaller proportion of the volume of concrete, then the total porosity of the concrete is lower, and hence its strength is higher. The above argument ignores any voids in the aggregate, but with normal aggregate these are minimal.

2.9.3.3 Effects of size and properties of aggregates on strength

At one time it was thought that the use of larger size aggregate leads to higher strength. This was due to fact that the larger the aggregate size , the lower is the total surface areas


Figure: 2.3 The relation between Strength and water/cement ratio of concrete (Shetty, 1993).

Figure: 2.4 The relation between Strength and cement/water ratio (Shetty, 1993).


and therefore the lower the requirement of the for the given workability. For this reason, a lower water/cement ratio can be which will result in higher strength.

However, later it was found that the use of larger size aggregate did not contribute tohigher strength as expected from the theoretical considerations due to the following reason:

Firstly, the larger maximum size aggregate gives lower surface area for development of gel bonds which is responsible for the lower strength of concrete.

Figure: 2.5 Influences of the aggregate/cement ratio on the strength of concrete (Neville, Brooks, 1987)

Secondly, bigger sizes of aggregate cause a more heterogeneity in the concrete which will prevent the uniform distribution of load when stressed.

Generally, high strength concrete or rich concrete is adversely affected by the use of large size aggregate. But in lean mixes or weaker concrete, the influences of size of aggregate get reduced.


It is interesting to note that in lean mixes larger aggregate gives highest strength while in rich mixes it is the smaller aggregate which yields higher strength. Figure 2.6 show the influences of maximum size of aggregate on compressive strength of concrete.(Cordon, 1963).

Figure 2.6 Influence of maximum size of aggregate on 28 days compressive strength of concrete of different richness. .(Cordon, 1963).

2.9.3.4 Gain of strength with age

The concrete develops strength with continued hydration. The rate of the gain of strength is faster to start with and the rate gets reduced with age. it is customary to assume the 28 days strength as the full strength beyond 28 days also. Earlier codes have not been permitted to consider this increase of strength beyond 28 days for design purposes. The increase in strength beyond 28 days used to get immersed with the factor of safety. With better understanding of the materials, progressive designers have been trying to reduce the factor for safety and make the structure more economical. In the direction, the increase if strength beyond 28 days is make into consideration in design of structures. Some of the more progressive codes have been permitted in this practice. Figure: 2.7 shows gain of strength of concrete with age.

2.9.3.5 Aggregate-cement Bond Strengths

It is only in the recent years that the aggregate cement bond strengths have been investigated with the object by finding out systematically their influence on the strength


of concrete. In fact, the strength of concrete is really derived from the bond between the paste and aggregate. In view of the micro cracks formed in the body of the paste, the measurement of the bond strength between paste and aggregate become difficult.

Figure: 2.7 Gain of strength with age.(Marsh,1986)

However, attempts have been made to find out the bond strength between gel and aggregate. This bond strength depends upon the surface texture of the aggregate, mycological nature of the aggregate and the specific surface of the gel. The inherent micro cracks that are generated within the body of the concrete influence the bond strength between paste and aggregate.

2.10 IMPORTANCE OF USE OF FLY ASH IN CONCRETE

A major use of fly ash in the construction industry is in production of high quality structural concrete. Fly ash contributes beneficial properties to the concrete while helping to maintain economy. These properties include compressive strength, lubrication and increased durability.

Fly ash spheres impart ball bearing lubrication to plastic concrete, enhancing workability at the same slump as ordinary concrete, while reducing water convenience. Enhanced workability contributes improved quality to structural concrete in several ways.


(A) Concrete pumping is made easier. Flow rate may be increased without increasing line pressure, and line blockages are reduced. Record pumping time is achieved as a result of the use of fly ash. The technique of injecting concrete into the bottom of the form from the pump house is made possible by the workability of the mix from the fly ash.

(B) From filling becomes easier. Fly ash concrete is more responsive to vibration, enabling forms to be fully filled more quickly and with less effort.

(C) Segregation is reduced due to increase cohesiveness and workability as well as resulting reductions in voids rock pockets and other defects. (Cost saving from reduced corrective action required on defects alone can be significant).

2.11 REMARKS

In this chapter, history of concrete and cement, type of cement, fly ash quality and their effect on concrete are explained broadly to clear the concept about them.

34 Properties of aggregate, preparation and test of concrete

CHAPTER 3

PROPERTIES OF AGGREGATE, PREPARATION AND TESTING OF CONCRETE

3.1 GENERAL

In this research, it has been undertaken to evaluate the strength gaining property of different locally available composite cement. Comparison of strength between curing and noncuring sample and also comparison of strength between locally available cement and ordinary Portland cement (OPC) is performed. Prior of the strength testing, physical and chemical properties of coarse aggregate and fine aggregate were performed with due care. The methods and procedure adopted for all this test and preparation of test sample are described in this chapter.

3.2 PROPERTIES OF COARSE AGGREGATE

As coarse aggregate, crashed coarse stone chips are used. For Mix design purpose fineness modulus, unit weight, voids in aggregates, absorption capacity, specific gravity are tested. This test performed according ASTM C117-84, ASTM C 29/C 29 M -91a, ASTM C136-84a and ASTM C 127-88.

3.2.1 Absorption capacity and Specific gravity of coarse aggregate

For the purpose of testing ASTM C127-88 method is used.specimen for the test is crushed stone.

ABSORPTION CAPACITY

Serial no

Oven dry wt. (gm) S.S.D .wt. (gm)

Wt. of saturated specimen in water (gm)

Absorption capacity

(%)

A B C (B-A)/AX100

1. 3149 3163 1995 0.45

SPECIFIC GRAVITY

Serial No. Bulk specific gravity A/(B-C)

Bulk specific gravity (Saturated surface dry)

B/(B-C)

Apparent Specific Gravity A/(A-C)

1. 2.70 2.71 2.73


3.2.2 Unit weight and voids in coarse aggregates Unit weight of the coarse aggregate is tested by the test method ASTM C29/ C29 M-91a. Tested sample is crushed stone chips. Nominal volume is ft3(7.08X 10-3 m3). Weight of the sample taken is 10.963 kg. Factor for the measure is 141.64 for the test. Unit weight: 10.963/7.08X10-3=1500 kg/m3

3.2.3 Sieve analysis and gradation of coarse aggregate Coarse aggregate are sieved to obtain fineness modulus and gradation chart. Test method used for this purpose is ASTM C 117-84.

Table 3.1Sieve analysis (coarse aggregate)

Sieve Size

SIEVE SIZE (mm)

Wt. of the materials retained (gms)

Percent of materials retained (rounded)

Cumulative %

retained

% Finer

21 2 63.5 0 0 0 100 2 50.8 0 0 0 100

11 2 38.1 0 0 0 100 1 25.4 0 0 0 100 19.05 1994 40 40 60 12.7 2824 57 97 3

3/8 9.525 162 3 100 0 6.25 15 0 100 0

No.4 5 4 0 100 0 No.8 2.36 0 0 100 0 No.16 1.18 0 0 100 0 No.30 0.0006 0 0 100 0 No.50 .0003 0 0 100 0 No.100 .0002 0 0 100 0 PAN 1

TOTAL 5000 100

Fineness Modulus,

F.M. = (40+97+100+100+100+100+100+100)/100 =7.4


Figure: 3.1 Gradation chart of coarse aggregate Gradation chart of coarse aggregate is shown in figure 3.1. from this figure the values of D10, D30 and D60 are 10.4, 10.6 and 10.9 respectively; D10, D30 and D60 are the particles size corresponding to 10, 30 and 60 percent finer respectively. The value of uniformity coefficient, Cu (Cu=D60/D10=1.04) and curvature coefficient, CZ (Cz= D302/D60xD10=0.99) are 1.04 and 0.99 respectively. As Cu is not greater than 4 and Cz is not between 1 and 3, the aggregate is not well graded but uniformly graded aggregate (Peck and Hanson, 1953).

3.3 PROPERTIES OF FINE AGGREGATE

As fine aggregate, Sylhet sand is used. For mix design purpose, fineness modulus, unit weight, absorption capacity and specific gravity are tested. all tests are performed according to ASTM C117-84, ASTM C136/84a, and ASTM C 128/84. The values of fineness modulus, unit weight, absorption capacity and bulk specific gravity are 2.56, 1580 kg/m3, 1.21 and 2.59 respectively.

3.3.1 Unit weight of fine Aggregate (Sylhet Sand)

Unit weight of the fine aggregate is tested by the test method ASTM C29/ C29 M-91a. Tested sample is Sylhet Sand. Nominal volume is 1/10 ft3 (2.83X 10-3 m3). Weight of the sample taken is 4.2 kg. Factor for the measure is 377.26 for the test. Unit Weight: 1580 kg/m3. Unit weightof the tested coarse aggregate is 1580 kg/m3.


Figure: 3.2 coarse aggregate (stone chips)

3.3.2. Absorption capacity and Specific Gravity of Fine aggregate Results of Absorption capacity and Specific Gravity of fine aggregate (Sylhet Sand) are follows

Sample Oven dry

Pyc +Water

Pyc+water +Sam

ple

SSD Sample

Absorption capacity

Specific Gravity

no sample (gm) (gm) (gm) (gm)

(%) Bulk Bulk

(SSD) Apparent

A B C A/(B+500-

C) 500/(B+50

0-C) A/(B+A-

C) 1. 494.02 1299 1606 500 1.21 2.56 2.59 2.64


3.3.1 Fineness modulus and Gradation of Fine aggregate

Coarse aggregate are sieved to obtain fineness modulus and gradation chart. Test method used for this purpose is ASTM C 117-84.Sample used is Sylhet sand.

Table 3.2 sieve analysis (Fine aggregate)

Sieve Size (ASTM)

Sieve Size (mm)

Wt. of the materials retained (gms)

% of the materials retained

(rounded)

Cumulative retained

(%)

% finer

No.8 2.36 16.02 3.2 3.2 96.8 No.16 1.18 103.87 20.8 24 76 No.30 .0006 168.11 33.6 57.6 42.4 No.50 .0003 160.19 32.0 89.6 10.4 No.100 .00015 44.85 9 98.6 1.4 No.200 .000075 4.27 0.9 99.5 0.5

Pan 2.65 0.5 100 TOTAL 5000

Fineness Modulus, FM= (3.2+24+57.+89.6+98.6+99.5)/100 =2.56

Figure: 3.3 Gradation Chart for fine aggregate.


Gradation chart of fine aggregate is shown in figure 3.3. From this figure the values of D10, D30 and D60 are 0.0003, 0.00048 and 0.03 respectively; D10, D30 and D60 are the particles size corresponding to 10, 30 and 60 percent finer respectively. The value of uniformity coefficient, Cu(Cu=D60/D10) and curvature coefficient, CZ (Cz = D302/D60xD10) are 100 and 0.02respectively. As Cu is not greater than 6 and Cz is not between 1 and 3, the aggregate is poorly graded aggregate (Peck and Hanson, 1953).

Figure: 3.4 Fine Aggregate (Sylhet sand)

3.4 CHOICE OF STRENGTH

Concrete is the core part of construction work. Strength of concrete is commonly considered to be its most valuable property, although in many practical cases other characteristics, such as durability, impermeability and volume stability, may in fact be more important. Nevertheless, strength usually gives an overall picture of the quality of concrete because it is directly related of the structural of cement paste. In our county, the strength that used is construction works with locally available cement that varies from 2000psi to 4000 psi or so on for 28 days compressive strength testing. So, as a representative one 2500psi and 4000psi are selected, and as representative of high


strength concrete 6000psi is selected. So desired strength, of this thesis is 2500psi, 4000psi, 6000psi.

3.5 CEMENT BRANDS

The locally available composite that are used for this tests are as follows:

1. Brand type-A

2. Brand type-B 3. Brand type-C

4. Brand type-D and

5. Ordinary Portland Cement. (Brand type-E)

3.5.1 Proportions of ingredients in cements

1. Brand-A:

Clinker: 65% ~79% Lime stone: 21%~ 35% Gypsum: 0%~5% 2. Brand-B:

Clinker: 70% ~ 79% S, PFA, LS: 21% ~ 30% Gypsum: 0% ~ 5%

3. Brand-C: Clinker: 65%~ 79% Gypsum: 0~5% Slag, Fly Ash, Limestone: 21%~ 35%

4. Brand-D: Clinker: 80%~94% Gypsum: 0~5% Slag, Fly Ash, Limestone: 06%~ 20%

5. Brand-E:( OPC) Clinker: 95%~100% Gypsum: 0~5%

3.6 TESTING AGES

With time, strength of concrete gains varies with the age of concrete. Initially strength gaining property is high and progressively continuous due to rate of hydration and initial


internal reactions of cement. So, to observe the change of strength of concrete, the concrete test cylinders are tested at the age of 3 days, 7 days, 28 days, 3 months and 6 months.

3.7 MOULD DIMENSION

Different dimensions of cylinders are used for concrete strength testing overall the world. 6 by12 and 4 by 8 are standard dimension of cylinder. In these test, 4 by 8 has been used.

Figure: 3.5 Testing cylinder mould

3.8 NUMBER OF SPECIMENS

Specimens are made for two types: 1. Curing sample (3 Nos) 2. Non curing sample (3 Nos) Number of cement brands: 5 Ages of testing: 5 ( 3 days,7 days, 28 days, 3 months, 6 months ) Number of strength: 3

So total number of specimen requires=2X3X3X5X5=450 Nos.


3.9 IDENTITY MARK FOR SPECIMENS

A303CU A303NC Here, A= cement brand. 3= strength concrete (3 for 2500 psi, 4 for 4000 psi and 6 for 6000psi). 03=age of test(3 for 3 days, 7 for7 days, 28 for 28 days, 3m for 3 months and 6m for 6 months) CU= Cu for curing sample (NC for Non Curing sample) For cement brand designation, A=Supercrete Cement. B=Shah Cement. C=Crown Cement. D=Seven Rings Cement. E=Ordinary Portland cement. 3.10 Preparation Procedure of Specimens (mixing, placing of concrete into molds) Preparation procedure of the test specimens are illustrated as the following pictures:

57 Strength of Concrete

CHAPTER 4

STRENGTH OF CONCRETE 4.1 GENERAL

The compressive strength of concrete is one of the most important and useful properties of concrete. In most structural applications, concrete is employed primarily to resist compressive stresses. In those cases where strength in tension and shear are of primary importance, the compressive strength is frequently used as a measure of these properties (ASTM C192). Therefore, the concrete making properties of various ingredients of mix are usually measured in terms of compressive strength. Compressive strength is also used as a qualitative measure for other properties of hardened concrete (ACI 318, 1989). No exact quantitative relationship between compressive strength and flexural strength, tensile strength, modulus of elasticity, wear resistance, fire resistance, or permeability have been established nor are they likely to be.

The compressive strength of concrete is generally determined by testing cubes or cylinders made in laboratory of field or cores drilled from hardened concrete at side or from the non-destructive testing of the specimen or the actual structure (ASTM C39-96).

Strength of concrete is its resistance to rapture. It may be determined in a number of ways, such as strength in compression, in tension, in shear, or in flexure (Appendix A). All these indicate strength with reference to a particular method of testing.

4.2 FACTORS AFFECTING CONCRETE STRENGTH

For given cement and acceptable aggregates, the strength that may be developed by workable, properly mixing of cement, aggregate and water (under the same mixing, curing and testing conditions) is influences by:

i. Ratio of cement to mixing water; ii. Ratio of cement to aggregate;

iii. Grading, surface texture, shape, strength and stiffness of aggregate particles; iv. Effective blending, desired slump, molding, vibrating and curing; v. Maximum size of aggregate and aggregate-cement bonding etc.

4.3 COMPRESSIVE STRENGTH OF CONCRETE

Compressive strength of concrete is determined according to ASTM C39-96. Figure 4.1 to 4.15 show the strength gain property of diffident branded cement at continuously cured and 14 days cured with time.

Figure 4.1 to 4.5 show the compressive strength gaining of concrete for strength of 2500 psi. For this strength, w/c ratio is 0.68. From this entire figure, in is shown that 14 days cured strength is quite higher than continuously cured strength approximately u

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A Study on Rate of Strength Gain of Concrete Mix Prepared With Locally Available Composite Cement

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