Unconfined compressive strength and free swelling potential of polymer stabilized sulfate bearing soils

Cementitious soil stabilizers such as lime and cement are widely used in the world because they are very effective to reduce the swelling potential of high plasticity index (PI) soils. But if sulfate is present in high PI soils, the calcium in lime or cement will bond with sulfate to form ettringite and thaumasite minerals, both of which result in significant swelling. Such swelling has led to various distresses on structures, such as residential buildings, parking lots, and pavements. This study explores using a liquid polymer as a substitute of cementitious stabilizers to stabilize sulfate rich high PI soil and investigates the improvement on soil strength and reduction on swelling. Unconfined compressive strength (UCS) and free swelling of a high PI soil with 2%- sulfate was studied in this research. The tests were conducted by adding polymer levels of 4, 7, 10, and 13% by weight. 4% lime stabilization was also studied in order to compare the results. In order to examine the adverse effect of ettringite formation, non-sulfate soil was also studied for UCS and free swelling. The study results showed significant increase in UCS of polymer stabilized soil. UCS of 535, 1025, 1510, and 1895 kPa was achieved at polymer additives of 4, 7, 10, and 13% respectively. 4% lime stabilized soil showed UCS of 700 kPa. Furthermore, the soaked UCS of polymer and lime treated soil was also evaluated. 5% polymer stabilized specimens showed soaked strength of 130 kPa, while, 4% lime stabilized non-sulfate and 2%-sulfate soil showed 360 and 120 kPa respectively. Free swelling test was performed for unstabilized, 4% lime stabilized, and 4 & 10% polymer stabilized soil. While unstabilized soil showed 24% swell, 4% lime stabilized soil resulted in 17% swell. However, polymer stabilization resulted in significant decrease of free swell value. 4% and 10% polymer treated soil showed a free swell value of 8%, and 2% respectively.