Elevated temperature effects on swelling pressure of compacted bentonite

Understanding the effects of temperature on hydro-mechanical behaviour of compacted bentonite is important for performance assessments of bentonite- based buffer, backfill and sealing systems in deep geological disposal of high-level radioactive wastes. Motivated by such applications, most past experimental studies were focused on highly compacted and high-quality bentonite. Such degrees of dry densities may not be economically or technically feasible for other emerging applications including as an alternative material to cement in plugging and abandonment of wells. A bespoke high-pressure high-temperature constant rate of strain (CRS) apparatus was developed for the work reported here to conduct a series of tests for evaluating the hydro-mechanical response of pre-saturated compacted bentonite to elevated temperatures. Experiments were performed with bentonite specimens with high impurity contents at a range of dry densities (1.1, 1.4 and 1.7 Mg/m3) and temperatures between 20oC and 80°C. The results show that temperature increase leads to the decrease of swelling pressure for all studied densities. Larger reductions of swelling pressure were observed with increasing dry densities suggesting the possibility of a larger exchange of pore water in the microstructure system of the clay. The transfer of water from micropores to macropores at elevated temperature is shown to be a key controlling process at high density compacted bentonite by which temperature affects the swelling pressure and hydraulic conductivity.