Quality Aggregates for Indiana Highways

IN TR O D U C TIO N Until recently aggregates were considered inert materials which, when mixed with some cementing agent, served as filler in concrete. This concept is far from reality. Research and experience have demonstrated that aggregates are physically and chemically active in ways that control their serviceability in concrete. Since these materials constitute about 75 per cent of the volume of the concrete in which they are used, engineers are very interested in the properties of aggregates. It has been found that certain aggregates contain materials which can have detrimental effects on portland cement concrete. Fortunately, Indiana has an abundance of excellent quality aggregate. Data collected at Purdue show that less than 10 per cent of the aggregate used in Indiana in the last 35 years contained enough of these harmful or “deleterious” materials to produce inferior concrete. However, the use of even this small percentage of inferior aggregates has resulted in con­ siderable consumer loss in terms of shorter life of structures and the necessity of employing more costly designs to offset aggregate weak­ nesses. Consequently, it is necessary to evaluate the quality of all aggre­ gates before they are used in concrete. It is the purpose of this paper to review some of the past and current literature related to the evaluation of concrete aggregates and to show how experience, service records, and laboratory research have been com­ bined to produce a background of sound technical information which can be used in the development of specifications for aggregates.