Industrial solid waste based sulfoaluminate materials for pollution cutoff wall: Biochar-driven hydration acceleration, microstructural densification, and life-cycle environmental benefits

Abstract

Rapid pollutant containment in contaminated sites requires cutoff materials with fast setting, early strength, high impermeability, and chemical resistance. This study develops a Sulfur-aluminum-ferric (SAF) binder synthesized from industrial solid wastes and modified with biochar (BC). The potential of this material as a soil-cement pollution cutoff wall was evaluated through strength experiments, microstructure analysis, permeability modeling, pollution cutoff validation, and life cycle assessment (LCA). The material attained a final setting time <1 h and met the 28-day unconfined compressive strength (UCS) requirement specified for cutoff walls as early as 16 h. BC accelerated hydration by promoting calcium silicate hydrate (C-S-H) and ettringite (AFt) formation, refined the pore structure, and improved interfacial transition zones (ITZ), resulting in ∼70 % lower intrinsic permeability. The visualization simulation of absolute permeability showed that the modified material has lower internal absolute permeability, effective porosity, and total flow rate, as well as higher tortuosity, pressure gradient, and more uniform internal pressure field. Sparse streamline distribution implied poor fluid transport capacity. Samples maintained stable performance in an acidic, alkaline, salt, and VOCs containing environments. BC also reduced the leaching concentration of heavy metals from the waste. Pilot-scale experiments confirmed the material's ability to prevent contaminant migration in actual contaminated sites. LCA revealed a 63.9 % reduction in global warming potential, along with significant decreases in ecotoxicity, acidification, and human carcinogenic toxicity relative to Portland cement. The integration of industrial solid waste and BC enhances engineering performance and environmental resilience, providing a potential material for pollution cutoff wall.

Keywords: Biochar modification; Impermeability; Industrial solid waste; Life-cycle assessment; Pollution cutoff wall; Sulfoaluminate cement.