Temperature-dependent swelling and compressibility behavior of microfiber-reinforced bentonite

Bentonite is widely used as a buffer material in deep geological repositories because its low hydraulic conductivity and swelling pressure help limit advective radionuclide transport. Elevated temperature, however, can cause drying and shrinkage, which may alter swelling behavior and reduce mechanical integrity. Fiber reinforcement has been proposed to mitigate these effects, but the behavior of fiber-reinforced bentonite at elevated temperature remains poorly understood. This study investigates the swelling pressure, compressibility, and consolidation behavior of glass microfiber-reinforced Na-bentonite at 22 °C and 50 °C with fiber contents of 0, 1, and 3 wt%. The fiber sensitivity of swelling pressure decreased by 42% over the 28 K temperature increase, from − 72.9 kPa/wt% at 22 °C to − 42.5 kPa/wt% at 50 °C, even though the overall swelling pressure increased with temperature. To interpret the results, a thermo-Barcelona Basic Model (BBM) framework with a volumetric homogenization fiber composite term was calibrated against the experimental data. The analysis indicates that the reduced fiber sensitivity at elevated temperature is mainly related to a decrease in the apparent fiber–matrix interfacial bond strength, τ b , from 16 to 9 kPa, whereas the bentonite-phase parameters λ(0) and p 0 changed only slightly. These findings suggest that the effectiveness of fiber reinforcement depends not only on fiber properties, but also on the thermal stability of the fiber–clay interface under hydrothermal conditions. Scanning electron microscopy (SEM) observations showed fiber–clay contact and clay coating on fiber surfaces, supporting the proposed interfacial mechanism. Overall, the results suggest that interfacial bond stability should be considered when selecting inorganic fiber reinforcement for engineered barrier materials subjected to coupled thermo-hydro-mechanical conditions.