Soil improvement by biomass polyions and compaction: Reinforcement, biodegradation resistance, and retention of heavy metal ions

Biomass-based alternatives to soil improvement by cement in geotechnical applications are increasingly considered owing to their renewability and low carbon footprint. We have elaborated a method of soil improvement by which soil is treated with self-organizing biomass-derived polyions, carboxymethyl cellulose (CMC), and chitosan (CS) and is consequently compacted by rammer. CMC and CS interact electrostatically and self-assemble into interpolyelectrolyte complexes (IPEC) having the morphology of thin films imparting the superior mechanical properties to the soil composite. Curing of soil with CMC and CS at m(CMC+CS)/m(soil) ratios below 1% and compaction improved the unconfined compressive strength (qu) of soil up to 500 kPa in a wet state (ca. 17% moisture content) and 2.5 MPa in a dry state (ca. 0% moisture content). Due to the superior complexing properties of CMC and CS towards transition metal ions, soil treatment with IPEC notably suppressed the leaching of Cu2+, Pd2+, and Cd2+ metal ions from the soil. Despite the intrinsic biodegradability of CMC and CS, their IPEC complexes and soil-IPEC composites showed good resistance toward biodegradation by the cellulase enzyme. Excellent soil reinforcement, suppressed biodegradability, and chemical functionality of biomass-derived IPECs hold promise in utilizing renewable polymers in geotechnical practices of ground improvement addressing the needs of the sustainable use of resources.