The effect of stone content, size, and shape on the engineering properties of a compacted silty clay

The compaction characteristics of clay-stone mixtures containing varying proportions of aggregate were studied using a homogeneous silty clay (CL) of glacial origin and crushed limestone aggregate. Three size gradations of limestone aggregate were each admixed with dried clay in 10 percent by weight increments from 10-80 percent. Limestone aggregate, subrounded in an abrasion apparatus, was mixed with the same clay in similar proportions to study the effect of stone shape. The clay-stone mixtures were then compacted by standard Proctor method to determine maximum dry density, optimum moisture content, and void ratio of each mix. Additionally, permeability and unconfined compressive strength tests were conducted on mixtures compacted to minimum of 95 percent maximum dry density and + or -2 percent optimum water content. Results shoe that there is an increase in maximum dry density and a corresponding decrease in void ratio as the stone content of a clay-aggregate mixture increases to 60-70 percent by weight regardless of stone size of shape. Permeability is generally not affected for up to 50 percent stone content, but increases 4 to 5 orders of magnitude between 50-70 percent stone. Unconfined compressive strength generally decreases with increasing stone content and stone size. The study shows that the addition of small size stone in small proportions can help improve the density of compacted silty clays without appreciably affecting other properties.--Modified journal abstract.