Moisture Hysteretic Behavior of Fine-Grained Soils Stabilized with Lime and Class C Fly Ash

Abstract

Seasonal conditions (e.g., rise in the water table, precipitation, freeze–thaw cycles, and wet–dry cycles) affect stabilized subgrade moisture conditions which, in turn, have a significant impact on in-service pavement performance. Studies have shown the effect of seasonal conditions on stabilized subgrade soils’ mechanical properties, including unconfined compression strength (UCS), modulus of elasticity (E), and resilient modulus (MR). There have been a limited number of studies addressing the hysteretic behavior of UCS, E, and MR in stabilized subgrade soils with moisture conditions. This study investigated the impact of moisture hysteresis on the UCS, E, and MR values of stabilized fine-grained soils following wetting, drying, and wetting–drying cycles. The results of this study can help predict changes in the bearing capacity of pavements subjected to seasonal conditions. Cylindrical specimens were first prepared with optimum moisture content and maximum dry unit weight. After each specimen’s moisture content was altered to attain the target moisture content, the specimens were tested for UCS, E, and MR values. The tests showed hysteretic behavior comparable to the soil–water characteristic curve; specimens subjected to wetting had lower MR values than those subjected to drying. The hysteretic behavior of the mechanical properties in stabilized specimens can be explained by the following: (1) wetting and drying accelerates chemical reactions, (2) soil suction changes within the pores, and (3) hydration and Born repulsion create repelling/attracting. Scanning electron microscope (SEM) micrographs show increased cementation products within specimens subject to drying and wetting–drying cycles. Findings also showed that pavement distresses, namely rutting and AC bottom-up fatigue cracking, changed as moisture content varied. However, the impact of moisture variations was more evident in a thin-HMA pavement section compared to a thick-HMA pavement section.