Curing method and performance evualation for cohesive and cohesionless soils stabilized with liquid polymers
An extensive laboratory testing program was carried out to investigate the optimal mixing and curing method, liquid content, and polymer-water ratio for two different liquid polymer soil stabilizers from the generic family of methylene diphenyl diisocyanate (Polymer M) and styrene acrylic (Polymer S) used on a poorly-graded sand and a sulfate-rich, high-plasticity clay. When the above-mentioned factors were determined, the performance of the treated soils was evaluated under different conditions: 1- short-term performance evaluation in which the treated specimens were tested for Unconfined Compressive Strength (UCS) shortly after their optimal curing; 2- Durability evaluation after a) 24 wet-dry cycles to evaluate the effect of moisture variation, b) 24 freeze-thaw cycles to evaluate the effect of seasonal changes, c) 2,000 hours of accelerated UV exposure to simulate the effect of extensive solar radiation and its consequent role in polymer degradation, d) 8 months of uncontrolled outdoor exposure in harsh climatic conditions to observe the combined effect of moisture variation, precipitation, and UV exposure on the UCS of specimens, e) fatigue response of the specimens under more than 1,000,000 cycles of repetitive loading to simulate the effect of traffic (sand specimens only), and f) Free swelling potential of the treated specimens to observe the efficiency of the polymers in reducing potential vertical rise (i.e. swelling) of the treated specimens (clay specimens only). The results of this study suggested the optimal mixing method, curing environment and polymer dosages are different in each polymer and soil. Sand specimens showed insignificant sensitivity to mixing method, while clay specimens were shown to provide better outcomes when polymer was added after the soil and water were properly mixed. For Polymer M, curing the treated specimens in air followed by water bathing was shown to result the strongest specimens, while heat curing neither played a beneficial or detrimental effect on the overall UCS of the specimens. As to polymer S, air curing or heat curing provided the best outcome, and the specimens showed moisture susceptibility when they were soaked in water. Polymer M showed better durability under freeze-thaw and wet-dry cycles, while Polymer S showcased susceptibility to moisture and temperature variation. Both specimens showed minimal strength loss due to polymer degradation under UV radiation, although Polymer M specimens were darkened in color and Polymer S were slightly lighter after exposure. Both specimens showed excellent performance under the Fatigue test, and showed better performance in reducing the swelling potential of the treated clays compared to lime treatment. Under controlled laboratory environment, the specimens treated with Polymer M and S showed approximately similar UCS, with Polymer S specimens being slightly more ductile.