Effect of freeze-thaw cycles on the physical and dynamic characteristic of modified Na-bentonite by KCl

The method of electrokinetic ion-exchange–modified bentonite can not only shorten the test period but also improve the efficiency of cation exchange. In this study, the X-ray fluorescence spectroscopy test, freeze-thaw (FT) cycle test, CT scan test, and dynamic triaxial test were performed on bentonite before and after modification. The results showed that cation exchange occurred between the bentonite layers and the free expansion rate was significantly reduced. With the increase in the number of FT cycles, the Na-bentonite samples did not change significantly, while the K-bentonite gradually appeared cracks, and the cracks developed significantly as the number of FT cycles increased. The FT cycles had a significant impact on the dynamic parameters of two bentonites, especially the first two FT cycles. When the strain was constant, the dynamic shear modulus of the two bentonites decreased first and then increased with the increase of the number of FT cycles, and then tended to be stable. The damping ratios of the two bentonites showed the opposite trend: the damping ratio of the Na-bentonite increased first and then decreased with the increase of the FT cycles, and the K-bentonite first decreased, then increased and then stabilized, indicating that the structure of K-bentonite was more stable. By comparison, it was found that the effects of FT cycles on the dynamic parameters of K-bentonite were smaller than those of Na-bentonite.