concrete technology

concrete technology

By

Dr Aminul Islam Laskar Associate Professor, Civil Engineering Department, National Institute of Technology, Silchar (Assam)

University Science Press (An Imprint of Laxmi Publications Pvt. Ltd.)

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 

Hyderabad Ranchi

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Foreword I feel privileged to write the foreword of the book, entitled Concrete Technology by Dr Aminul Islam Laskar, Associate Professor of Civil Engineering, National Institute of Technology Silchar. From a pile of books on the subject, what makes this book interesting is the effort taken by the author to make the subject very interesting to the first timers as well as to the professionals. The author presented the concepts in a very lucid and simple manner to be attractive for the target audience. The book covers most of the recent developments in concrete material science. Also, extensive references are made to IS codes and practical design considerations throughout the book for easy clarity and understanding. Thus the book should serve as a textbook for undergraduates and a reference compendium for practicing civil engineers. I hope the prospective readers will greatly benefit from the book.

Dr Bishwajit Bhattacharjee Professor of Civil Engineering Indian Institute of Technology, New Delhi

(v)

Preface Concrete has become indispensable in construction of modern buildings, bridges, nuclear structures, off shore structures and in many other applications. This is generally preferred for desired strength and high durability during the service life of the structure. Concrete is the second largest material consumed by human civilization now a days just after water. Over the recent years, there is a huge increase in the concrete production throughout the world. The subject has, therefore, been incorporated in various institutes to make this material familiar to students. But the number of books in the market is still limited. Present book has been written in a simple and lucid manner incorporating the recent developments of the subject so that the future engineers are well acquainted with the subject during their undergraduate study. Present book contains fundamentals of the subject concrete technology such as hydration of cement, cement types, concrete making materials, workability, hardened properties of concrete, durability, mix design, chemical and mineral admixtures, special concretes, high performance concrete, self compacting concrete, non-destructive testing, waste materials in concrete. The book will serve as a textbook at undergraduate level in Civil Engineering in Indian Universities, NITs and IITs. In the present semester system of engineering colleges, teachers as well as students should be able to finish the course covering entire syllabus. Present book has been written in a more comprehensive and concise manner suitable for undergraduate students. Moreover, recent and advanced topics have also been included for which students have to refer foreign books quite often. Inclusion of some recent topics particularly self compacting concrete, high performance concrete, rheology of concrete, some sophisticated and special techniques in concrete technology, use of waste materials in concrete are definitely some of the attractions of the book. This comprehensive book will serve as a text and guide book to undergraduate and even postgraduate students, concrete technologists, material scientists, practicing engineers and all users of concrete. If any errors are discovered by readers, I would be grateful to be informed so that future editions may be corrected. —Author

(vii)

Contents

1. Introduction



2. Hydraulic Cements

1—4 5—21

Formation of Portland Cement

5

Composition of Portland Cement

6

Hydration of Cement

7

Microstructure of Hydrated Cement Paste

10

Setting

12

Heat of Hydration

13

Fineness of Cement

15

Models of Hydrated Cement

15

Mechanical Properties of hcp 16 Soundness of Cement

17

Types of Cement

18

3. Aggregates and Water

22—33

Coarse Aggregate

22

Fine Aggregate

23

Aggregate Characteristics

24

Thermal Properties of Aggregates

31

Gap-graded Aggregate

32

Water

33



4. Workability

34—46

Different Parameters on Workability

35

Measurement of Workability

36

Bleeding and Segregation

45

Comments on Existing Workability Tests

46



5. Concrete in Plastic and Early Stage

47—54

Settlement Cracks

47

Plastic Shrinkage Cracks

50

Temperature Cracks

52

Recommended Prevention Methods

53



6. Chemical Admixtures 55—61

Retarding Admixtures

55

Accelerating Admixtures

56 (ix)

(x) Air Entraining Agent

56

Plasticizers

57

Superplasticizers

57

Viscosity Modifying Admixtures

60

Anti-Bacterial Admixtures

61



7. Mineral Admixtures 62—74

Fly Ash

62

High Volume Fly Ash Concrete

66

Silica Fume

68

Rice Husk Ash



71

Ground Granulated Blast Furnace Slag

73

Calcined Clay

74



8. Rheology of Concrete

Rheology

75—83



75

Constitutive Equations for Fluid Flow

76

Thixotropy

76

Measurement of Rheological Parameters Measurement Techniques



77



Data Processing in Rheometers

78

Some Artifacts in Rheological Measurements Some More Topics of Rheology

78



Torque-Speed Relationship in Coaxial Rheometer

79

9. Strength

80

82 84—96

Concrete in Compression

84

Gel-Space Ratio

87

Strength of Transition Zone

87

Factors Affecting Compressive Strength

88

Stress-Strain Curve in Compression

91

Tensile Strength of Concrete

92

Impact Strength

94

Cyclic Loading or Fatigue

94

Maturity

95

Creep of Concrete

95



10. Durability

97—115

Sulfate Attack

97

Acid Attack

99

Alkali Aggregate Reaction

100

Carbonation

101

(xi) Abrasion

103

Freezing and Thawing

104

Corrosion of Rebar

105

Effect of Sea Water on Concrete

114

Biological Degradation

115

Salt Crystalization

115

Delayed Ettringite Formation

115



11. Concrete Mix Design

116—125

Strength Requirements

116

Factors in the Choice of Mix Proportioning

118

Aci Method

118

Indian Standard Method

121

Acceptance and Compliance Criteria

12. High-Performance Concrete

124 126—142

High Performance Concrete (Hpc) 126 Theoretical Considerations

127

Materials Preparation

129

Procedure for Production in Laboratory

129

Mix Proportioning

130

Properties of Hpc 134 Testing of Hpc 140 Applications of Hpc 141 Considerations for Hpc 141

13. Self-Compacting Concrete

143—156

Development of Scc 143 Why Self-Compacting Concrete

143

Basic Principles and Requirements

145

Workability Tests for Scc 147 Mix Design of Scc 152 Acceptance Criteria for Scc 154 Adoption of Scc in the Precast Industry

155

Present Status of Scc 155

14. Fiber Reinforced Concrete

157—167

Principle of Fiber Reinforcement

157

General Characteristics

158

Classification of Frc 159 Mechanics of Fiber Reinforcement

159

Production of Frc 162

(xii) Some More Properties of Sfrc 163 Polypropylene Fibers

164

Ultra High Performance Frc 166

15. Non-Destructive Testing of Concrete

168—179

Rebound Hammer Method

168

Pullout Test

169

Pull-off Test

170

Resonant Frequency Method

171

Ultrasonic Pulse Velocity Method

173

Core Cutting Test

178



16. Additional Topics in Concrete Technology

Mercury Intrusion Porosimetry

180—194 180

X-ray Diffraction Analysis (Xrd) 183 Scanning Electron Microscopy (Sem) 183 Adsorption Methods

186

Special Concretes

189

17. Waste Materials in Concrete

195—205

Waste Materials

195

Waste Glass

197

Waste Rubber

202

Waste Plastic

204

References 206—207 Index 208—211

Chapter

1

Introduc tion Ever since civilizations first started to build, the human race has sought a material that binds stones into solid formed mass. The Romans mixed lime (i.e., burned limestone) with volcanic ash from Mount Vesuvius that produced structures of remarkable durability. During the Middle Ages, the art of making hydraulic cement (cement that hardens when it comes in contact with water) became lost and it was not until the year of 1824 that the hydraulic cement (now commonly known as Portland cement) reappeared when it was patented by a Leeds builder named Joseph Aspdin. The name “Portland cement” was given originally due to the resemblance of the colour and quality of the hardened cement to Portland stone (limestone quarried in Dorset). The most widely used modern construction material is concrete that is made by mixing Portland cement with sand, crushed rock and water. Man consumes no material except water in such tremendous quantities. Concrete is neither strong nor tough as steel, so why is it the most widely used engineering material? There are number of reasons. Firstly, Concrete possesses excellent resistance to water. Unlike wood and ordinary steel, the ability of concrete to withstand the action of water without serious deterioration makes it an ideal material for building structures to control, store and transport water. The second reason for wide spread use of concrete is the ease with which structural concrete elements can be formed into a variety of shapes and sizes. This is because freshly made concrete is of a plastic consistency, which permits the material to flow into prefabricated formwork. The third reason for the popularity of concrete with engineers is that it is usually the cheapest and most readily available material in the job. The principal ingredients for making concrete—Portland cement and aggregate are relatively inexpensive and are more commonly available in most areas of the world. In addition, large amounts of many industrial wastes can be recycled as a substitute for the cementitious material or aggregates in concrete. Therefore, in the future, considerations of energy and resource conservation are likely to make the choice of concrete as a structural material even more attractive. Although the fundamental cement types have been unchanged over last four decades, certain cement properties have changed significantly. Most changes emanate from the new cement manufacturing methods. Broadly speaking, ordinary Portland cement manufactured during the

1

2

Concrete Technology

last 25 years gains strength more rapidly than that produced 40 years ago. This gives commercial benefits: formwork can be struck earlier and construction can proceed more rapidly. However, this results in a shorter period of effective curing. Why, then, improvements in cement manufactures led to structural problems? For years, the primary criterion of the concrete acceptability was its 28 days compressive strength. With ‘new’ cements, the same strength achieved in the past was attained at a higher water/cement ratio, so the contractor was justified in using this ratio- and hence a lower cement content—for the same workability. The resulting concrete was more permeable than the concrete made with the old cement, resulting in a greater risk of carbonation and penetrability by aggressive agents. Problems arose because designers did not appreciate that the concrete in the structure was inferior in long-term quality especially with respect to durability, despite the specification remaining the same.

Fig. 1.1: Toyota Arrows Bridge in Japan

The attempt of developing new materials from the locally available raw materials like agricultural and industrial wastes is worldwide. Studies showed that the use of waste materials to produce different kind of building materials would not only reduce the construction cost but also help to improve the economy of the developing countries. Moreover, there has been an increasing demand for the use of cement in modern days. The cost of cement is high due to the high cost of cement plant and high production cost. In addition, cement manufacturing is localized in the areas where raw materials are abundant. The cost of transportation adds substantially to the cement cost for the consumer at any distance from the point of manufacturing. Pulverized Fly Ash (PFA) is described nowadays as a by-product, but 40 years ago it was considered to be a waste product. Other siliceous materials such as Rice Husk Ash (RHA) and metakaolin are also used in some parts of the world. The most common problem with concrete is shrinkage, which results in cracking. Shrinkage takes place within the Hydrated Cement Paste (HCP), and so the cement is responsible. Creep is not always harmful, but usually has undesirable effects, notably a time-dependent increase and deflection and also a loss of prestress. It is the hcp that undergoes creep. Alkali-silica and alkali-carbonate reactions are induced by the alkalis in cement; sulfate attack involves tricalcium



Introduction

3

aluminate in the cement. Some other types of chemical attack involve leaching of calcium hydroxide, which is a major product of the cement hydration, or even of calcium silicate hydrates which originate from the same source. It is impossible to make concrete, as we know it, without Portland cement. However, cement contenet should be minimized, balancing technical advantages and disadvantages on one end, and cost on the other. These methods have been steadily developed and improved during the last 50 years. The use of high strength concrete has become a common practice in many applications throughout the world for many decades, especially for high-rise buildings, long span bridges and repair and rehabilitation works (Fig. 1.2). Moreover, during the last decade, developments in mineral and chemical admixtures have made it possible to produce concrete with relatively much higher strength than was thought possible. High strength concrete is not a revolutionary material; rather, it is a development of normal strength concrete. Hence, special attention and detail considerations are required to produce high strength concrete.

Fig. 1.2: Burj Dubai in UAE

Portland cement concrete is considered to be a relatively brittle material. Apart from its excellent properties, concrete shows a rather low performance when subjected to tensile stress. When subjected to tensile stress, unreinforced concrete will crack and fail. The traditional solution to this problem is reinforced concrete, where reinforcing bars or prestressed steel bars inside the concrete elements are capable of absorbing the appearing tensile stresses. Another rather recent development is Steel Fiber Reinforced Concrete (SFRC). By adding

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