Effect of Moisture Content on the Mechanical Behavior of Base Course Materials

Abstract: This study presents laboratory testing results on how moisture content affects the mechanical behavior of unbound base course materials. Dense-Graded Base (DGB) aggregate, Recycled Asphalt Pavement (RAP), and Recycled Concrete Aggregate (RCA) collected from across Wisconsin were evaluated as representative base materials under various moisture conditions. Resilient Modulus (MR) and Permanent Deformation (PD) were measured using repeated load triaxial tests at three moisture levels: optimum moisture content (OMC), OMC−3%, and OMC+3%. These levels represent dry, optimal, and wet conditions, simulating typical field moisture variations during pavement service. The results show that moisture content significantly impacts both MR and PD. MR was highest at the dry side of OMC and decreased notably when the moisture exceeded OMC. Under wet conditions (OMC + 3%), the base materials became significantly less stiff and exhibited greater permanent deformation under load. These trends were consistent for both DGB and RCA; however, RAP showed less sensitivity to moisture content, with minimal differences in MR and PD across the three levels of moisture content. Overall, the findings emphasize the importance of moisture management in pavement base layers. Maintaining water content near the optimum level results in higher stiffness and less permanent deformation, thereby enhancing structural performance. Excess moisture, on the other hand, significantly reduces base course stability, underscoring the need for proper drainage and compaction practices. By demonstrating similar moisture-dependent behavior in both conventional and recycled base materials, this study informs the selection of materials. It guides moisture control strategies to ensure consistent performance in varying environmental conditions.