Thermal–Induced Fracture Mechanics Characteristics of Sand–Bentonite Composites

In hydraulic barriers and waste disposal sites, sand and bentonite mixtures are often used as backfill or liners. This research focuses on the importance of understanding how to safely store radioactive and solid waste long–term. This is the first study in the literature to explore how temperature affects damage in sand–bentonite mixtures using fracture mechanics. The findings revealed that more bentonite increases sensitivity to temperature, reduces cohesion, and increases internal friction. Moreover, results showed that higher temperatures and bentonite content decreased fracture toughness and created significant damage zones at crack tips. Scanning electron microscopy and interactive 3D images showed that shear damage mainly facilitates the sliding and rolling of coarser grains at high temperatures, leading to particle alignment along failure planes. Non–linear numerical analyses with a cohesive zone model revealed that the greatest traction opening and sliding in the cohesive crack occurred at 80 and 25°C for the 30B-70S specimens. The relationships between fracture toughness and common soil mechanical properties at the investigated temperatures were also investigated. The fracture toughness test results showed that increasing temperature and bentonite content reduced the fracture toughness of the 10B-90S samples by 30% at room temperature and by 30% at 80°C.