Crack mitigation and moisture retention in sand-clay mixtures under drought: Effects of biopolymer and fiber reinforcement

Global warming intensifies droughts and extreme heat, accelerating soil cracking and land degradation. Sand-clay mixtures (SCM) exhibit complex drying behavior due to their heterogeneous structure. Thus, sustainable drought mitigation strategies are essential to ensure the stability and performance of SCM in arid environments. This study investigates the effects of biopolymer (BMG) and palm fibers (PFs) on the drought resilience of SCM with different sand contents (15%, 30%, 50%, and 70%). Laboratory tests at 50 °C evaluated evaporation, water retention, and desiccation cracking in SCM treated with varying BMG (0%-0.15%) and PF (0%-0.6%) contents. Microstructural mechanisms were analyzed using scanning electron microscopy (SEM) and nuclear magnetic resonance (NMR). Results show that sand addition enlarges pores, accelerates evaporation, but reduces cracking by up to 91.76% at 70% sand content. BMG fills pores and enhances moisture retention, reducing the crack intensity factor by 99.02% at 0.15% content, although gel hardening increases brittleness. PFs alleviate this brittleness by forming a stress-dissipating network that enhances ductility and increases the air-entry value from 2.14 kPa to 2.42 kPa, thereby improving water retention. The combined use of 0.15% BMG and 0.6% PFs extends the evaporation duration by 37.5%, balancing the brittleness and heterogeneity of individual treatments. Overall, BMG and PFs effectively improve soil water retention, suppress evaporation, and mitigate cracking, offering an eco-friendly and sustainable approach to improve the drought resilience of SCM, with potential applications in soil stabilization, geotechnical infrastructure protection, and land restoration in arid and hot regions.