Stabilizing sulfate-rich high plasticity clay with moisture activated polymerization

• The mixing method and curing time for a moist-activated polymer are proposed to stabilize sulfate-rich high PI soil.
• The dosage effect on the strength and swelling potential of the stabilized soil is determined.
• The susceptibility of the stabilized sulfate-rich soil in water is assessed.

Cementitious soil stabilizers such as lime and cement are well known to cause swelling and, possibly, reduction in strength when used to stabilize sulfate-rich soil with high plasticity index (PI). This study explores using a moisture activated liquid polymer - a member of Methylene diphenyl diisocyanate (usually addressed as MDI) family, as a substitute of cementitious stabilizers to stabilize sulfate-rich high plasticity soil. The effect of mixing method, curing time, and polymer dosage on the unconfined compressive strength (UCS) and free swelling potential of polymer stabilized high plasticity clay with 2% sulfate (20,000 ppm) was evaluated in this research. In addition, the susceptibility of lime and polymer stabilized sulfate-rich soils in water was compared. It was found that the mixing method has a great impact on the properties of the stabilized soil, i.e., to obtain the maximum strength the soil should first be mixed with water before the polymer is added. Under moist conditions, the UCS increased significantly with curing time until 4 days. With the determined mixing method and curing time, 0, 4, 7, 10, and 13% of polymer were added to the sulfate-rich high plasticity clay to assess the dosage effect on the UCS and swelling potential. The results showed significant increase in UCS and decrease in swelling potential of the polymer stabilized soil with the increase of polymer dosage. The study further indicated that even though lime or polymer stabilized sulfate-rich high plasticity clay samples were subjected to significant strength degradation after soaked in water for 2 days, the polymer stabilized soil had much higher residual strength.