RECYCLED GYPSUM AND RICE HUSK ASH AS ADDITIVES IN THE STABILIZATION OF EXPANSIVE SOIL

Expansive soils pose great risk to the structural integrity of many overlying structures. Given the impracticality of mechanical means of ground improvement in smaller projects, chemical stabilization is preferred. An economic and sustainable way of improving weak soils can be achieved with waste utilization of discarded materials as enhancing additives. Clay loam from Kauswagan, Lanao del Norte were treated with varied proportions of recycled gypsum and rice husk ash. Evaluation of the effectiveness of the admixtures were done based from criteria and laboratory tests listed by NSCP 2010 Section 303.5 and ASTM D4609. Addition of gypsum as lone additive increases plasticity, while further addition of RHA finally diminishes plasticity. Compaction characteristics at 15% gypsum + 10% RHA had maximum dry density increased by 1.918 kN/m(3) and optimum water content decreased by 26%. While overall decrease in swelling was observed, only specimens with 15% gypsum + 10% RHA were considered non-expansive (EI < 20) by NSCP 2010. Mean compressive strengths of specimen were enhanced with a peak value of 1.128 MPa at 15% gypsum. Considering criteria from ASTM D4609 and NSCP Section 303.5, an admixture combination of gypsum and RHA can be considered effective in improving expansive soils.