ABSTRACT
Portland cement concrete is a simple material in appearance but has a very complex internal nature. Despite its internal complexity, the versatility, durability, and economy of concrete have made it the world’s most used construction material. This can be seen in the variety of structures for which it is used, from highways and bridges to buildings and dams (Figure 5.1). Concrete is a mixture of Portland cement, water, and aggregates, with or without admixtures. Portland cement and water form a paste that hardens due to chemical reactions between the cement and water. The paste acts as a glue, binding the aggregates, composed of sand and gravel or crushed stone, into a solid rock-like mass. The quality of the paste and aggregates dictates the engineering properties of concrete construction. Paste qualities are directly related to the amount of water used in relation to the amount of cement. The less water used, the better the quality of the concrete. Reduced water content results in improved strength and durability and reduced permeability and shrinkage. Fine and coarse aggregates make up 60 to 75% of the total volume of the concrete (Figure 5.2); therefore, selection of aggregate is important. Aggregates must be of adequate strength, resistant to exposure conditions, and durable.
