Enhancing the Mechanical Performance and Volumetric Stability of High-Plasticity Clay Using Recycled Portland Cement and a Hydrophilic Crystalline Additive.

Highly plastic (CH) soils may soften, swell, and undergo considerable deformation when exposed to moisture changes, reducing their mechanical performance and potentially affecting the serviceability of foundations. Although lime is commonly used to stabilize clayey soils, Portland cement was selected to develop a cementitious matrix compatible with a hydrophilic crystalline additive. The additive was incorporated to investigate whether its moisture-activated interaction with the cementitious components could improve strength and reduce volumetric instability.

The CH soil had a liquid limit of 63.2% and a plasticity index of 32.7%. Six conditions were evaluated: undisturbed soil sample (UDS), untreated reconstituted soil (UTS), treated reconstituted soil with recycled Portland cement (TSRC), treated reconstituted soil with recycled cement and additive (TSRCA), treated reconstituted soil with Portland cement (TSC), and treated reconstituted soil with Portland cement and additive (TSCA). Treated mixtures contained either 13% cementitious material or 8% cementitious material plus 5% crystalline additive, by total dry mass. Cylindrical specimens measuring 35 mm in diameter and 95 mm in height were tested in unconfined compression at 7, 14 and 28 days. One-dimensional swelling and consolidation tests were performed following ASTM D4546 and ASTM D2435, respectively, under incremental loading up to 0.153 kg/cm². UTS exhibited an unconfined compressive strength of 1.958 kg/cm^2. At 7 days, TSRC, TSRCA, TSC, and TSCA reached 2.825, 4.028, 23.535 and 20.15 kg/cm², respectively. At 28 days, TSRCA and TSCA increased to 4.466 and 27.542 kg/cm². Relative to UDS, the treated specimens achieved maximum reductions of 72.6% in swelling and 90.2% in vertical deformation.

The results indicate that, under the evaluated preparation and curing conditions, recycled Portland cement and the additive may contribute to improving the mechanical response of CH soils while reducing their volumetric instability. The proposed treatments may support soil-improvement strategies that reduce conventional cement demand and limit moisture-related geotechnical problems.