Novel composite polymer-amended bentonite for environmental containment: Hydraulic conductivity, chemical compatibility, enhanced rheology and polymer stability

Engineering Properties of Novel Vertical Cutoff Wall Backfills Composed of Alkali-Activated Slag, Polymer-Amended Bentonite and Sand

“…The MSBS-PAC consisted of MgO, GGBS, sand, and PAC-amended CB. According to previous studies [8,[15][16][17]28], the dry weight of CB in the backfill material was 10% of that of sand, while the dry weight of GGBS and MgO was 5% of that of sand, i.e., dry weight ratio of GGBS to MgO was controlled at 9:1. The PAC was selected as an additive with a dosage of 2% (dry weight ratio of PAC to CB).…”

“…The lightweight reactive magnesia (MgO) was supplied by a chemical plant in Shanghai, China, which was a white powder with a MgO content of 78.5%, activity of 90~100 s, density of 3.56 g/cm 3 , and pH of 10.59. The polyanionic cellulose (PAC) was produced by Hunan Pujie Co., Ltd. (Changsha, Hunan Province, China) [28]. PAC had a particle size of less than 0.15 mm, specific gravity of 1.26, weight average molecular weight of 1,730,000, apparent viscosity of 35 mPa•s, a degree of substitution of 1.4, and a pH of 7.3.…”

“…A hydrophilic polymer such as cross-linked superabsorbent polymer (SAP) as an internal curing material was found to be able to reduce the autogenous shrinkage and change the pore size distribution and mechanical properties of cement-based materials [24,25]. Polyanionic cellulose (PAC), a commonly used industrial hydrogel and linear anionic polymer, can increase the viscosity of bentonite suspensions, which is a water-soluble cellulose ether polymer derivative obtained by the chemical modification of natural cellulose [26][27][28]. Moreover, PAC was found to be a promising additive in improving the chemical compatibility of conventional bentonite and backfill consequently [29].…”

“…Moreover, PAC was found to be a promising additive in improving the chemical compatibility of conventional bentonite and backfill consequently [29]. Du et al [27] and Fu et al [28] have employed PAC (2% dry weight) as an additive for bentonite to reduce the hydraulic conductivity and improve the chemical compatibility of the bentonite filter cake under heavy metal exposure conditions. Shen [29] showed that PAC addition considerably reduces the hydraulic conductivity of SB backfill to tap water and heavy-metal-impacted groundwater.…”

“…Shen [29] showed that PAC addition considerably reduces the hydraulic conductivity of SB backfill to tap water and heavy-metal-impacted groundwater. The reasons are attributed to the pore-filling effect caused by the PAC hydrogel and the "consumption" of multi-valence cations that are aggressive to the thickness of the diffuse double layer (DDL) of montmorillonite mineral in the conventional bentonites [27,28]. Using PAC-amended bentonite to replace conventional bentonite is believed to be effective in tackling this issue.…”