Shear strength deterioration of geopolymer stabilized loess under wet-dry cycles: mechanisms and prediction model

Abstract

The loess was stabilized using geopolymer (GP). Triaxial compression tests were conducted on stabilized loess with varied GP contents subjected to wet–dry cycles. The degradation law of the shear strength of the stabilized loess after varied wet–dry cycles was evaluated and an empirical model for predicting the shear strength was proposed. The chemical composition of the hydration products, the microstructure and pore size distribution of stabilized loess were investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM) and mercury intrusion porosimetry (MIP) tests. The degradation mechanisms of GP stabilized loess under wet–dry cycles were discussed based on the experimental results. The experimental results show that compared with untreated soil, the shear strength of stabilized soils is significantly improved with the increasing GP content, i.e. the cohesion and internal friction angle increase by 260% and 43%, respectively. The shear strength of stabilized loess decreases with the increasing ratio of porosity to GP volumetric fraction ( ) in a power function. It indicates that GP stabilization can remarkably improve the durability of loess under wet–dry cycles. The stabilized loess with 10% and 15% GP can maintain over 75% of their original shear strength, but those with 5% GP shows evident deterioration in shear strength after nine wet–dry cycles. The wet–dry cycling has greater impact on the degradation of peak deviatoric stress and cohesion than that of internal friction angle. An empirical model was proposed and validated for predicting the degradation in shear strength of the GP stabilized loess under wet–dry cycles, considering influence of the GP content, confining pressure and the number of wet–dry cycle. The experimental results of XRD, SEM and MIP show that the main hydration products of GP are calcium silicate hydrate (CSH) and calcium aluminosilicate hydrate (CASH), which fill the soil pores and enhance the bonding between soil particles. Due to this reason, a denser microstructure develops and the cohesion of the stabilized loess increases, which consequently improves the shear strength of the GP stabilized loesses. Moreover, the wet–dry cycle results in the expansion of soil pores and the formation of new fissures, which destructs the bonding between soil particles and reduces the shear strength of the stabilized loess.

Keywords

• loess
• geopolymer
• wet–dry cycle
• shear strength deterioration
• stabilizing mechanism
• prediction model