Effect of Geometric Characteristics of Coarse Aggregates on Compaction Characteristics of Soil-Aggregate Mixtures

This paper reports the results of a laboratory study to investigate the effect of the geometric characteristics of coarse aggregate particles on the compaction characteristics of soil-aggregate mixtures. Six coarse aggregate materials with discernible geometric characteristics, including both pitrun gravel and crushed stone materials, were used in the study. The geometric characteristics of these materials were determined by the "particle index" test, a procedure developed at the University of Illinois particularly for the quantitative evaluation of these characteristics. The results of this investigation show that the volume of the voids in a soil-aggregate mixture of a given gradation under a standard laboratory compactive condition decreases more or less linearly with decreasing values of the particle index of the coarse aggregates; that is, as the coarse aggregate particles become more spherical, rounded, and smoothly surfaced. The conclusion that the density of a soil-aggregate mixture varies not only with the gradation of the mixture but also with the geometric characteristics of the coarse aggregate fraction appears to be deserving of some consideration in tht:: construction control of soil-aggregate roads.