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 17 1.1 Concrete as a Structural Material ....................................... 17 1.2 Components of Modern Concrete ....................................... 18 1.3 Types of Concrete ............................................... 19 1.4 Properties of Hardened Concrete and their Significance ........................... 19 1.5 Units of Measurement ............................................. 21 1.6 Test your Knowledge ............................................. 21 1.7 Suggestions for Further Study ........................................ 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 89 6 Hydraulic Cements 91 6.1 Hydraulic and Nonhydraulic Cements .................................... 91 6.1.1 Definitions, and the Chemistry of Gypsum and Lime Cements ................... 91 6.2 Portland Cement ............................................... 91 6.2.1 Manufacturing Process ........................................ 92 6.2.2 Chemical Composition ........................................ 92 6.2.3 Determination of Compound Composition from Chemical Analysis ................ 93 3 4 CONTENTS 6.2.4 Crystal Structures and Reactivity of Compounds .......................... 93 6.2.5 Fineness ............................................... 95 6.3 Hydration of Portland Cement ........................................ 95 6.3.1 Significance .............................................. 95 6.3.2 Mechanism of Hydration ....................................... 96 6.3.3 Hydration of the Aluminates ..................................... 96 6.3.4 Hydration of the Silicates ....................................... 97 6.4 Heat of Hydration ............................................... 98 6.5 Physical Aspects of the Setting and Hardening Process ........................... 99 6.6 Effect of Cement Characteristics on Strength and Heat of Hydration .................... 99 6.7 Types of Portland Cement ........................................... 100 6.8 Special Hydraulic Cements .......................................... 101 6.8.1 Classification and Nomenclature ................................... 101 6.8.2 Blended Portland Cements ...................................... 101 6.8.3 Expansive Cements .......................................... 103 6.8.4 Rapid Setting and Hardening Cements ................................ 104 6.8.5 Oil-Well Cements ........................................... 104 6.8.6 White or Colored Cements ...................................... 105 6.8.7 Calcium Aluminate Cement ..................................... 106 7 Aggregates 111 8 Admixtures 123 9 Proportioning Concrete Mixtures 137 9.1 Significance and Objectives .......................................... 137 9.2 General Considerations ............................................ 138 9.3 Procedures ................................................... 140 9.4 Sample Computations ............................................. 142 10 Concrete at Early Ages 147 III Recent Advances and Concrete in the Future 165 11 Progress in Concrete Technology 167 12 Advances in Concrete Mechanics 201 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 5 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 ap- parent 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 distri- bution 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 there- fore 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