A state-of-the-art review of polymers used in soil stabilization

This paper provides a review of the research on use of polymers for soil stabilization in pavement and geotechnical engineering. First, the properties impacting the effectiveness of widely used polymer classes, including geopolymers, biopolymers, and synthetic organic polymers are discussed. These include types and ratios of the precursor and activator of geopolymers, molecular weight, particle size, charge, conformation, solubility, viscosity, pH, and moisture behavior of organic polymers. Next, the paper reviews the mechanisms governing stabilization of soils with the various polymer classes. The key mechanisms for organic polymer–clay interactions are electrostatic forces and entropy increase, which contribute differently depending on whether the polymer is cationic, neutral, or anionic. On the other hand, the interactions between polymers and coarse-grained soils composed predominantly of sands are mainly attributed to three types of structural changes: a thin film covering sand particles, the formation of polymer ties connecting noncontacted neighboring particles, and the development of adhesion between particles. The mechanism of geopolymer stabilization is through the formation of a sodium and/or calcium aluminosilicate gel, which bind the surrounding soil particles and harden into a denser, stronger matrix. The engineering properties of the soil types after stabilization using polymers, including strength improvement, permeability reduction, swell and shrinkage inhibition, and durability and stability enhancement are discussed. Finally, the paper highlights the challenges for wider use of polymer stabilization of soils including limited evaluation standards, life-cycle cost considerations, and moisture susceptibility. To this end, some future research direction to promote the widespread use of polymers in soil stabilization are recommended including the need for establishment of standard testing protocols, evaluation of in-situ properties of polymer stabilized soils, resolution of durability issues and further in-depth examination of stabilizing mechanisms.