Mechanical Properties and Mechanism Studies of Stabilization of Siliceous and Calcareous Subgrade Soils with Polyelectrolytes

Abstract

Using polymers in soil stabilization is prevalent over the past decade. The improvements in mechanical properties and the underlying mechanisms have been of high interest among researchers and civil engineers. In this study, two oppositely charged polyelectrolytes, poly(sodium 4-styrene sulfonate) (PSS) and poly(diallyldimethylammonium chloride) (PDADMAC), not used in soil stabilization before, are evaluated as soil stabilizers in terms of the unconfined compressive strength, resilient modulus, and fracture toughness. Three types of soils including two sandy soils and one clay soil are used. Both polymers improved the strength of the soil and the improvement in strength increases with the increasing molecular weight, higher concentrations of solution and the increasing dosages added to the soil. This trend applies to all the three soils studied. In addition to strength improvement, both polymers improved the resilient modulus and the fracture toughness of the soil. PSS is found to be more effective than PDADMAC since PSS-treated specimens showed higher strength than PDADMAC at the same dosage. PSS also works at very low dosages of 0.2% while PDADMAC requires higher dosages to be effective. Morphology changes in the soils after polymer treatment are examined using scanning electron microscopy (SEM). Aggregation of fine soil particles and linkage between adjacent soil particles are observed under the microscope, which result in well-bound soil-polymer matrix, leading to better mechanical properties. Adsorption of PSS and PDADMAC on palygorskite is measured using ultraviolet-visible spectroscopy (UV-Vis) and the adsorption capacity of each polymer on the clay mineral is determined. The surface energies of the polymer powders are determined via Washburn method using the dynamic contact angle measuring device and tensiometer (DCAT). The work of adhesion between the polymers and pure calcite, quartz, and palygorskite is determined. Higher work of adhesion is obtained between PSS and the soil minerals, indicating stronger binding between PSS and the soil than PDADMAC.