Research on Concrete Aggregates

Portland cement concrete has been used extensively for many years as a construction material in bridges, buildings, highway pavements and other structures. Numerous structures and pavements that have been in service for decades illustrate the good durability and value of con­ crete when properly used in engineering construction. For example, the first concrete pavement built in the United States was still in use and in good condition after more than 50 years (1)*. Like any other engineering material, concrete will fail structurally if subjected to overloads. Durability, as used in this paper, refers to the ability of the concrete to withstand the attack of natural agents of weathering and deterioration, without consideration of the structural adequacy of the material to carry the loads to which it is subjected. Figures 1 and 2 illustrate the excellent performance obtained from hundreds of miles of concrete pavement and many structures in In­ diana. Although concrete has, in general, proven to be a durable material, there are many examples of non-durable concrete—concrete that has failed or deteriorated because of the effects of natural weathering or chemical reactions. Unsightly cracking, spalling, scaling and pop-outs, as well as general crumbling, disintegration and failure of concrete structures may be observed in all sections of the country. The concrete with poor durability characteristics represents only a small percentage of the pavements and structures that have been built, however, the cost due to decreased life of the concrete is a very important item (2). The financial losses, inconveniences, and in some cases, dangers to the public that may result from only an occasional failure have led to extensive work and study in the field of concrete durability. Many and varied reasons for failure of concrete structures have been shown to exist. When we consider that portland cement is an ex-