Effect of High-Temperature History on the Swelling Characteristics and Chemical Composition of Kunigel-V1 Bentonite

Kunigel-V1 (KV1) bentonite samples were cured at 130, 200, and 300°C for 30, 60, 120, 240, 480, 1,000, and 1,500 days to grant them different temperature histories. Swelling strain and swelling pressure tests were conducted to obtain equilibrium swelling strains (εeq) and equilibrium swelling pressures (peq), respectively, to evaluate high-temperature history effects on swelling characteristics. Some specimens after swelling strain and swelling pressure tests were sent to X-ray diffraction (XRD) tests to get basal spacing of montmorillonite (d001). Subsequently, cured KV1 samples underwent methylene blue adsorption (MB), cation exchangeable capacity (CEC), leached cation (LC), and CaCO3 content (CCaCO3) tests. These tests showed the following: (1) temperature history affected εeq and d001 after swelling strain tests, but peq and d001 after swelling pressure tests were not affected; (2) MB and CEC were not affected by temperature history, which suggests that the montmorillonite amount was not affected by temperature history; (3) limited effects were found from temperature history to LCNa+, LCMg2+, and LCK+, while temperature history strongly affected LCCa2+; and 4) CCaCO3 was not affected under 130 and 200°C. However, it was found decreased under 300°C. Finally, temperature history effects on chemical compositions of KV1 were discussed carefully to elucidate temperature history effects on swelling characteristics.