Effects of calcium carbonate on hydro-mechanical properties of bentonite

To simulate characteristic changes of the bentonite mixing with CaCO 3 crystals that precipitate from groundwater around the high-level radioactive waste repositories, different amounts of CaCO 3 powders were mixed in the bentonite. In this study, four series of bentonite/CaCO 3 mixtures were prepared with different contents of CaCO 3 powders. A series of swelling, compression and direct shear tests were conducted on the bentonite/CaCO 3 samples using deionized water. Terzaghi consolidation theory was adopted to compute the hydraulic conductivity of bentonite/CaCO 3 mixtures. The results demonstrated that the final swelling strain decreased with increasing vertical stress and the content of CaCO 3 powders. The compression index decreased slightly with increasing CaCO 3 content. It was found that as the CaCO 3 content increased, the hydraulic conductivity of bentonite/CaCO 3 mixtures decreased. There was a peak point in the shear strength of unsaturated samples with the differences of the CaCO 3 content. The cohesion of unsaturated samples increased first and then decreased, but saturated samples presented the opposite character. It could be seen from the scanning electron micrograph that the existence of CaCO 3 powders filled pores of bentonite/CaCO 3 mixtures and made the structure denser.