Using the swelling rate calculated from the swelling index test to evaluate the influence of concrete alkali concentration and temperature on bentonite swelling properties

Bentonite is used as a buffer material in the final disposal sites of high-level radioactive waste. Its expansibility is affected by cement-based materials with high pH values; however, existing studies rarely use actual cement-based materials. This study applied the swelling rate of the swelling index test to evaluate the influence of actual concrete alkali concentrations and temperatures on the swelling properties of bentonites. The results showed that when bentonite was placed in the concrete pore solutions with high pH value at 23 and 80°C, the swelling capacity was obviously reduced, whereas the low-pH concrete solution did not reduce the swelling capacity of bentonite. The number of alkali metal ions in the low-pH concrete reacting with the bentonite was 0.8–1.8% of that in the highly alkaline concrete. The temperature rise increased the swelling rate of the bentonite. The required test period of the bentonite swelling index test was short. This method observed an obvious increase in the main swelling stage, which was favorable for judging the influence of concrete alkalinity on bentonite. Thus, the swelling rate calculated from the swelling index test was appropriate for evaluating the influence of actual concrete solutions and temperature on the swelling properties of bentonite.