Effects of thermal-saline coupled conditions on swelling properties of bentonite analyzed on the basis of the fractal model

Swelling deformation tests were conducted on bentonite in NaCl, KCl, and CaCl 2 solutions at 25, 50, and 80 ℃. Utilizing a fractal e-p e model, the swelling coefficient K was employed to quantify thermal-saline coupling effects. Results indicated a negative correlation between K and temperature, attributed to increased water molecule kinetic energy restraining crystal layer swelling. While K remained constant in NaCl, it decreased with rising concentration and temperature in KCl and CaCl 2 due to intensified cation exchange. The relative magnitude of K varied by concentration: the sequence was NaCl > KCl> CaCl 2 at 0.1 M, but shifted to NaCl> CaCl 2 > KCl at 1.0 M. This reversal is not a simple “synergy. ” It reflects a shift from Ca 2+ -dominated electrostatic suppression at low concentration to K + -dominated fixation and mineral alteration at high concentration. XRD analysis confirmed mineral stability in NaCl and CaCl 2 ; however, significant montmorillonite dissolution was observed in KCl at 80 ℃ and 1.0 M, leading to a marked reduction in K . The intrinsic cation exchange capacity ( CEC ) is a material property and does not change with ion type; however, the apparent CEC and exchangeable cation composition measured after reaction can change in KCl due to K + fixation and mineral alteration.