Enhanced resistance to desiccation cracking of polymer–bentonite mixtures: an experimental investigation of underlying mechanisms

Polymers have been shown to enhance the resistance of swelling clay soils to desiccation cracking, a critical property in engineering applications, particularly in waste containment facilities. However, the microscopic and macroscopic mechanisms driving this improvement remain poorly understood. Additionally, the influence of different mixing methods on these mechanisms is not well-established. While dry mixing (DM) is more convenient for onsite implementation, wet mixing (WM) offers intercalation between clay and polymer, resulting in potentially more durable stabilization outcomes. In this paper, key properties related to desiccation cracking of a polymer–clay mixture were measured. The mixture was synthesized by amending Na-bentonite with sodium carboxymethyl cellulose (Na-CMC) using DM and WM. Soil water-retention characteristics curves (SWCC), swelling and shrinkage potential, tensile strength, and pore-size distribution by mercury intrusion porosimetry (MIP) were measured for both mixtures and untreated bentonite. Compared to pure bentonite, mixtures were found to have slightly reduced air-entry values, significantly lower swelling and shrinkage potentials, and higher tensile strengths. In all experiments, DM exhibited superior performance compared to WM. MIP analysis of the amended mixtures revealed a more porous structure compared to untreated bentonite.