EFFECT OF VARIATIONS IN COARSE-AGGREGATE GRADATION ON PROPERTIES OF PORTLAND CEMENT CONCRETE

The effect of variations in coarse-aggregate agradation on properties of a highway concrete mixture was studied by testing numerous batches of laboratory-preparaed concrete. The water-cement and aggregate-cementratios were the same for all batches; the only variable was the grading of the natural gravel used as coarse aggregate throughout the investigation. Each batch contained a known coarse-aggregate grading, and the entire group of gradings examined represented the variation determined to occur in typical pavement concrete production. The data were obtained and analyzed in a manner that allowed evaluation of the importance of variations in gradation of natural gravel as a source of variabtion in slump, compressive strength, and unit weight of field-produced concrete. On the basis of the results obtained in the investigation, typical field variations in coarse-aggregate gradation appear to have a relatively small effect on slump variablity compared to the combined effect of other factors, a surprisingly large effect on compressive strength, and little effect on the compactibility of a low-slump paving mixture.