Physical and Chemical Behavior of Four Cement-Treated Aggregates

Cement-treated aggregate (CTA) is commonly used to provide a stable base for pavements that are placed over weak soil subgrades. Because CTA reduces the thickness of the aggregate required to provide a durable base by approximately one-half, using it as a bearing layer for pavement can limit the quantity of unsuitable soil that must be excavated and removed, and can reduce the erodability of the stabilized soils. However, the field performance of CTA is variable, even when prepared according to set standards. This laboratory-based investigation explored the effects of fines content, cement content, mineralogy, pH, and freeze/thaw cycling on the unconfined compressive strength of cement-treated aggregate. The mineralogy of the base aggregate was found to make a significant difference in the strength of the CTA, with strength increasing in the following order: mica, limestone, and diabase. The granite aggregate yielded variable results, but the strengths were generally on the order of those determined for the diabase aggregate. The pH of the samples also correlated well, with the measured strengths increasing as the pH increased. As was anticipated, increasing the cement content increased the measured unconfined compressive strength of cylinders that were not subjected to freeze/thaw cycling. The same basic trend was observed in cylinders that were subjected to freeze/thaw cycling; however, the increase was less pronounced in the cylinders that were subjected to physical abrasion during thaw cycles. The fines content did not significantly influence the unconfined compressive strength of the cylinders that were not subjected to freeze/thaw cycling; however, the fines content appeared to confer a protective effect to the durability of the cylinders that were subjected to freeze/thaw. For the freeze/thaw test conditions (with and without physical abrasion), the unconfined compressive strength increased as the fines content was increased.