Effects of Fines Content on Hydraulic and Mechanical Performance of Unbound Granular Base Aggregates

The fines content of a granular aggregate base (GAB) material (<0.074 mm) is highly variable and often related to the crushing process, transportation, and stockpiling in a quarry or site. The influence of fines content on the drainage and stiffness of five different GAB materials was investigated through a series of laboratory resilient moduli, permanent deformation, and hydraulic conductivity tests. An increase in fines content up to 6%-10% by weight increased the summary resilient modulus of the GAB materials. The permanent deformation of all GABs increased significantly with an increase in fines content from 0% to 14% by weight. Up to two orders of magnitude decrease in GAB hydraulic conductivities was observed with increasing fines content in the gradation. The drainage qualities of the GAB materials can generally be classified fair according to commonly used specifications, with an exception of the ones prepared at 2% fines content. In order to achieve satisfactory mechanical and hydraulic performance, the fines content should be limited to 8% and gravel-to-sand ratio should be kept between 1.4 and 1.65.