Hydraulic properties of sodium polyacrylate-modified bentonite

Hydraulic properties of sodium polyacrylate-modified bentonite–sand mixtures

Yang, Wei / Zhang, Shaoqiu / Xie, Pan / Xia, Xiaohui / Liu, Xueying

Abstract Sodium polyacrylate (PAA-Na) was selected as a polymer to modify sodium bentonite (NaB) to improve its chemical compatibility, thereby improving the hydraulic properties of polymer-modified bentonite–sand mixtures (PMBS). In this study, scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS) were used to clarify the modification mechanism of polymer-modified bentonite (PMB). The free swell index and hydraulic conductivity tests were conducted to determine the effects of ions, pH, non-prehydration, and wet–dry cycles on the hydraulic properties of PMBS and sodium bentonite–sand mixtures (NaBS). SEM–EDS results confirmed that a cluster of bentonite particles, including micropores, were wrapped by a three-dimensional crosslinked network structure of PAA-Na. Compared with the free swell index (FSI) of NaB (35 mL/2 g), the FSI of PMB increased to 86 mL/2 g in deionized water, and the FSI of PMB was found to be 2–3 times higher than that of NaB in all tested solutions. The results of hydraulic conductivity tests showed that with identical compaction levels, PMBS, with hydraulic conductivities of less than 1 × $ 10^{−8} $ cm/s in all permeant liquids, had lower hydraulic conductivities than that of NaBS. In addition, PMBS exhibited excellent self-healing capacity, with almost all the surface cracks being able to heal after nine wet–dry cycles involving tap water, so that PMBS could always maintain a very low hydraulic conductivity of around 5 × $ 10^{−9} $ cm/s. In contrast, the volume of NaBS shrank by 8.15% after nine wet–dry cycles, leading to an increase of four orders of magnitude in its hydraulic conductivity.