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CONCRETE Microstructure, Properties and Materials P. Kumar Mehta Paulo J. M. Monteiro October 20, 2001 Contents Foreword to the First Edition 5 Preface to the First Edition 7 Preface to the Second Edition 11 Acknowledgments 13 I Structures and Properties of Hardened Concrete 15 1 Introduction to Con...

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CONCRETE Microstructure, Properties and Materials P. Kumar Mehta Paulo J. M. Monteiro October 20, 2001

Contents

Foreword to the First Edition

5

Preface to the First Edition

7

Preface to the Second Edition

11

Acknowledgments

13

I Structures and Properties of Hardened Concrete

15

1

Introduction to Concrete 1.1 Concrete as a Structural Material . . . . . . . . . . . . 1.2 Components of Modern Concrete . . . . . . . . . . . . 1.3 Types of Concrete . . . . . . . . . . . . . . . . . . . . 1.4 Properties of Hardened Concrete and their Significance 1.5 Units of Measurement . . . . . . . . . . . . . . . . . . 1.6 Test your Knowledge . . . . . . . . . . . . . . . . . . 1.7 Suggestions for Further Study . . . . . . . . . . . . .

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17 17 18 19 19 21 21 21

2

The Structure of Concrete

23

3

Strength

33

4

Dimensional Stability

47

5

Durability

61

II Concrete Materials, Mix Proportioning, and Early-Age Properties 6

Hydraulic Cements 6.1 Hydraulic and Nonhydraulic Cements . . . . . . . . . . . . . . . . . . . . 6.1.1 Definitions, and the Chemistry of Gypsum and Lime Cements . . . 6.2 Portland Cement . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6.2.1 Manufacturing Process . . . . . . . . . . . . . . . . . . . . . . . . 6.2.2 Chemical Composition . . . . . . . . . . . . . . . . . . . . . . . . 6.2.3 Determination of Compound Composition from Chemical Analysis 3

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91 91 91 91 92 92 93

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CONTENTS

6.3

6.4 6.5 6.6 6.7 6.8

6.2.4 Crystal Structures and Reactivity of Compounds . . . . . . 6.2.5 Fineness . . . . . . . . . . . . . . . . . . . . . . . . . . . Hydration of Portland Cement . . . . . . . . . . . . . . . . . . . . 6.3.1 Significance . . . . . . . . . . . . . . . . . . . . . . . . . . 6.3.2 Mechanism of Hydration . . . . . . . . . . . . . . . . . . . 6.3.3 Hydration of the Aluminates . . . . . . . . . . . . . . . . . 6.3.4 Hydration of the Silicates . . . . . . . . . . . . . . . . . . . Heat of Hydration . . . . . . . . . . . . . . . . . . . . . . . . . . . Physical Aspects of the Setting and Hardening Process . . . . . . . Effect of Cement Characteristics on Strength and Heat of Hydration Types of Portland Cement . . . . . . . . . . . . . . . . . . . . . . . Special Hydraulic Cements . . . . . . . . . . . . . . . . . . . . . . 6.8.1 Classification and Nomenclature . . . . . . . . . . . . . . . 6.8.2 Blended Portland Cements . . . . . . . . . . . . . . . . . . 6.8.3 Expansive Cements . . . . . . . . . . . . . . . . . . . . . . 6.8.4 Rapid Setting and Hardening Cements . . . . . . . . . . . . 6.8.5 Oil-Well Cements . . . . . . . . . . . . . . . . . . . . . . . 6.8.6 White or Colored Cements . . . . . . . . . . . . . . . . . . 6.8.7 Calcium Aluminate Cement . . . . . . . . . . . . . . . . .

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93 95 95 95 96 96 97 98 99 99 100 101 101 101 103 104 104 105 106

7

Aggregates

111

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Admixtures

123

9

Proportioning Concrete Mixtures 9.1 Significance and Objectives . . 9.2 General Considerations . . . . 9.3 Procedures . . . . . . . . . . . 9.4 Sample Computations . . . . .

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10 Concrete at Early Ages

III

Recent Advances and Concrete in the Future

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137 137 138 140 142 147

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11 Progress in Concrete Technology

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12 Advances in Concrete Mechanics

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13 The Future of Concrete

231

Foreword to the First Edition

Professor Mehta has presented the subject of concrete in a remarkably clear and logical manner. Actually, he has adopted a rather revolutionary approach, rejecting the dry and pedantic presentations of past texts, in order to address concrete as a living material, both in itself and in its application to structures and facilities built to serve society. While this book accurately reflects the latest scientific advances in concrete structure and technology, it recognizes that working with concrete is an “art.” Thus he has structured the book’s arrangement and presentation from the point of view of the professional engineer charged with designing and building facilities of concrete. He introduces not only the lates understanding of this complex material but the new and exciting techniques that enable dramatic improvements in the properties and performance of concrete. The book is written primarily as an introductory text for Civil Engineering undergraduate students, but graduate students and professionals alike will find it useful for its lucid explanations and comprehensive treatment of the many interactive aspects. Ben C. Gerwick, Jr. Professor of Civil Engineering University of California, Berkeley

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6

CONTENTS

Preface to the First Edition

Portland cement concrete is presently the most widely used manufactured material. Judging from world trends, the future of concrete looks even brighter because for most purposes it offers suitable engineering properties at low cost, combined with energy-saving and ecological benefits. It is therefore desirable that engineers know more about concrete than about other building materials. There are several difficulties in preparing a scientific treatise on concrete as a material. First, in spite of concrete’s apparent simplicity, it has a highly complex structure; therefore, the structure-property relations that are generally so helpful in the understanding and control of material properties cannot be easily applied. Concrete contains a heterogeneous distribution of many solid components as well as pores of varying shapes and sizes which may be completely or partially filled with alkaline solutions. Analytical methods of material science and solid mechanics which work well with manufactured materials that are relatively homogeneous and far less complex, such as steel, plastics, and ceramics, do not seem to be very effective with concrete. Second, compared to other materials, the structure of concrete is not a static property of the material. This is because two of the three distinctly different components of the structure – the bulk cement paste and the transition zone between the aggregate and the bulk cement past – continue to change with time. In this respect, concrete resembles wood and other living systems. In fact, the word concrete comes from the Latin term concretus, which means to grow. Strength and some other properties of concrete depend on the cement hydration products, which continue to form for several years. Although the products are relatively insoluble, they can slowly dissolve and recrystallize in moist environments, thus imparting to concrete the ability to heal microcracks. Third, unlike other material which are delivered in a ready-to-use form, concrete often has to be manufactured just before use at or near the job site. Typically, a book on concrete begins with a detailed account of the composition and properties of concrete-making materials, e.g., cements, aggregates, and admixtures. This is followed by descriptions of methods for mix proportioning; equipment for batching, mixing, and transporting; and the technology of compacting, finishing, and curing concrete. The properties of concrete as a material and the principles governing them appear much later in the book, and are usually lost in a maze of non-scientific information, such as test methods, specifications, and applications. This book is not intended to be an exhaustive treatise on concrete. Written primarily for the use of undergraduate students in civil engineering, it is proposed to present the art and science of concrete in a simple, clear, and scientific manner. The term scientific manner does not imply an emphasis on theoretical physics, chemistry, or mathematics. Because of the highly complex and dynamic nature of the material, theoretical models have produced only “theoretical concretes,” and have proven to be of little value in practice. In fact, there is a popular joke in the concrete industry: What is abstract cannot be concrete. Most of our knowledge of the properties of concrete and the factors affecting it which forms the basis for current codes of concrete practice comes not from theoretical studies, but from laboratory and field experience. This experience provides adequate explanations for the properties of concrete and how and why they are influenced by various factors. By a scientific treatment of the subject, therefore, the author means that, as far as possible, structure-property relations are emphasized; that is, in addition to a presentation of the state of the art, rational explanations are provided for the observed behavior. In regard to the organization of the subject matter, the author has taken a somewhat different than traditional approach. In many countries, since most of the concrete is ready-mixed and since the ready-mixed concrete industry has increasingly assumed the responsibility of selecting concrete-making materials and mix proportions, it is not essential to emphasize 7

8

CONTENTS

these topic in the beginning of a book. Most civil engineers involved with design, construction, and analysis of concrete structure are interested primarily in the properties of hardened concrete. The first part of this three-part book is therefore devoted to the properties of hardened concrete: for example, strength, elastic modulus, drying shrinkage, thermal shrinkage, creep, tensile strain capacity, permeability, and durability to physical and chemical processes of degradation. Definition of terms, the significance and origin of each property, and controlling factors are set forth in a clear and concise manner. The second part of the book deals with the production of concrete. Separate chapters contain current information on the composition and properties of commonly used cements, aggregates, and admixtures. One chapter is devoted to the principles underlying the proportioning of concrete mixtures; another describes the properties of concrete at an early age and how they influence the operations to which freshly produced concrete is subjected. The latter also includes a broad discussion of quality assurance programs, such as accelerated tests, in situ tests, and statistical control charts. In the third part of the book, advances in concrete technology resulting from innovations to adapt the material for special engineering applications are described. Current information on composition, properties, and applications of several types of special concrete is provided, including structural lightweight concrete, heavyweight concrete for nuclear shielding, high-strength concrete, high-workability concrete, shrinkage-compensating concrete, fiber-reinforced concrete, concretes containing polymers, and mass concrete. The final chapter includes some reflections on the future of concrete as a building material. These reflections are based on engineering properties, cost economy, energy savings, and ecological considerations. Many unique diagrams, photographs, and summary tables are included to serve as teaching aids. New terms are indicated in boldface type and are defined when they appear first in the text. In the beginning of each chapter, a preview is given; at the end a self-test and a guide to further reading are provided. When the book is to be used as a text in a course in civil engineering materials, depending on the level at which instruction is being offered, individual instructors may wish to omit a part of the material from some chapters (e.g., chapters on cements and admixtures may be judged as too comprehensive for an undergraduate course), or supplement the others with additional reading (e.g., chapters on strength and dimensional changes may be judged as too elementary for a graduate course). The field of concrete is vast and human effort is never perfect. Therefore, the readers may find shortcomings in this book. This author is conscious of some of the omissions. For instance, a large amount of excellent literature on concrete which comes from outside the United States has not been included in the list of references, in part because the author is not very familiar with these publications. Also limitations of space were a major constraint. It is hoped that this deficiency can be made up by referring to the books and reports that are listed for further study at the end of every chapter. Again, several important subjects are not covered. It is a good idea for civil engineers to know about architectural concrete, repair and maintenance of concrete structures, and methods of testing concrete-making materials (cement, aggregate, and admixtures). Regrettably, in a book of this size it was not possible to include all the material that was considered useful. In the era of computers it might have been desirable to give more space to mathematical concepts developed for predicting the properties of concrete: for example, drying shrinkage, creep, cracking, and durability. Some of the work reported in the published literature is intellectually stimulating and indeed should be used for deeper and advanced study. On the other hand, a lot of the work is based on questionable assumptions about the micro-structure of the material and is therefore of limited value. The author’s failure to distinguish between the significant and the insignificant in this area of endeavor is largely responsible for its exclusion from the book. It is hoped that individual instructors and students can make up this deficiency on their own. The author, however, would like to add a word of caution. Since concrete tends to behave like living systems, it cannot be left solely to mechanistic treatments. The nature of the material is such that as a whole it is different from the sum of its parts. Therefore, the properties of the material are destroyed when it is dissected into isolated elements, either physically or theoretically. In his book The Turning Point, F. Capra, commenting on the systems view of living systems, says that the reductionist description of organisms can be useful and may in some cases be necessary, but it is dangerous when taken to be the complete explanation. Several thousand years ago, the same view was expressed in Srimad Bhagvad Gita: That knowledge which clings to one single effect as if it were the whole, without reason, without foundation in truth, is narrow and therefore trivial. My advice to students who will be tomorrow’s engineers: In regard to models, mathematical abstractions, and computer programs developed to predict the properties of concrete, by all means keep an open mind. But never forget that like the human world, the world of concrete is nonlinear and has discontinuities within the nonlinearities. Therefore, empirical

9

CONTENTS observations from laboratory and field experience will have to continue to supplement the theory. 27 August, 1985

P. Kumar Mehta University of California, Berkeley

10

CONTENTS

Preface to the Second Edition

Due to favorable reaction from the readers, especially from the education community, the key features of the first edition are retained in this revised edition. In the first part of the three-part book, the microstructure and properties of hardened concrete are described. Only minor revisions are made to the chapters on microstructures (Chapter 2), strength (Chapter 3), and durability of concrete (Chapter 5). However, the chapter on dimensional stability (Chapter 4) has been rewritten to clarify further the viscoelastic behaviour of concrete and to include a comprehensive treatment of thermal shrinkage and stresses, which are usually responsible for cracking in structures that are more than one meter thick. The second part of this book, Chapters 6–10, deals with concrete production. Separate chapters contain state of the art reports on the composition and properties of concrete-making materials, namely cement, aggregates, and admixtures, followed by chapters on mix proportioning and early age properties of concrete. Again, only minor revisions have been necessary to the chapters in this section, except that in Chapter 10 a description of plastic settlement cracks and crazing is included in a section on general review of cracks in concrete. The third part of the book, which contains a significant portion of the new material, should be of considerable int...