There is a direct relationship between population and urbanization. During the last 100 years, the world population has grown from 1.5 to 6 billion and nearly 3 billion people now live in and around the cities. Seventeen of the 20 megacities, each with a population of 10 million or more, happen to be situated in developing countries where enormous quantities of materials are required for the construction of housing, factories, commercial buildings, drinking water and sanitation facilities, dams and canals, roads, bridges, tunnels, and other infrastructure.
And the principal material of construction is portland cement concrete. By volume, the largest manufactures product in the world today is concrete. Naturally, design and construction engineers need to know more about concrete than about other materials of construction. This book is not intended to be an exhaustive treatise on concrete. Written primarily for the use of students in civil engineering, it covers a wide spectrum of topics in modern concrete technology that should be of considerable interest to practicing engineers.
For instance, to reduce the environmental impact of concrete, roles of pozzolanic and cementitious by-products as well as superplasticizing admixtures in producing highly durable products are thoroughly covered. One of the objectives of this book is to present the art and science of concrete in a simple, clear, and scientific manner. Properties of engineering materials are governed by their microstructure. Therefore, it is highly desirable that structural designers and engineers interested in the properties of concrete become familiar with the microstructure of the material. In spite of apparent simplicity of the technology of producing concrete, the microstructure of the product is highly complex.
Concrete contains a heterogeneous distribution of many solid compounds as well as voids of varying shapes and sizes that may be completely or partially filled with alkaline solution. Compared to other engineering materials like steel, plastics, and ceramics, the microstructure of concrete is not a static property of the material. This is because two of the three components of the microstructure, namely, the bulk cement paste and the interfacial transition zone between aggregate and cement paste change with time. In fact, the word concrete comes from the Latin term concretus, which means to grow.
The strength of concrete depends on the volume of the cement hydration products that continue to form for several years, resulting in a gradual enhancement of strength. Depending on the exposure to environment, solutions penetrating from the surface into the interior of concrete sometimes dissolve the cement hydration products causing an increase in porosity which reduces the strength and durability of concrete; conversely, when the products of interaction recrystallize in the voids and microcracks, it may enhance the strength and durability of the material.
This explains why analytical methods of material science that work well in modeling and predicting the behavior of microstructurally stable and homogeneous materials do not seem to be satisfactory in the case of concrete structures. In regard to organization of the subject matter, the first part of this three-part book is devoted to hardened concrete microstructure and properties, such as strength, modulus of elasticity, drying shrinkage, thermal shrinkage, creep, tensile strain capacity, permeability, and durability to various processes of degradation. Definition of each property, its significance and origin, and factors controlling it are set forth in a clear manner.
The second part of the book deals with concrete-making materials and concrete processing. Separate chapters contain state-of-the-art reviews on composition and properties of cements, aggregates, and admixtures. There are also separate chapters on proportioning of concrete mixtures, properties of concrete at early ages, and nondestructive test methods. The third part covers special topics in concrete technology. One chapter is devoted to composition, properties, and applications of special types of concrete, such as lightweight concrete, high-strength concrete, high-performance concrete, self-consolidating concrete, shrinkage-compensating concrete, fiberreinforced concrete, concretes containing polymers, and mass concrete.
A separate chapter deals with advances of concrete mechanics covering composite models, creep and shrinkage, thermal stresses, and fracture of concrete. The final chapter contains some reflections on current challenges to concrete as the most widely used building material, with special emphasis on ecological considerations. A special feature of the book is the inclusion of numerous unique diagrams, photographs, and summary tables intended to serve as teaching aids. New terms are indicated in italics and are clearly defined. Each chapter begins with a preview of the contents, and ends with a self-test and a guide for further reading.
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