Effects of calcium carbonate on hydro-mechanical properties of bentonite

Abstract

To simulate characteristic changes of the bentonite mixing with CaCO3 crystals that precipitate from groundwater around the high-level radioactive waste repositories, different amounts of CaCO3 powders were mixed in the bentonite. In this study, four series of bentonite/CaCO3 mixtures were prepared with different contents of CaCO3 powders. A series of swelling, compression and direct shear tests were conducted on the bentonite/CaCO3 samples using deionized water. Terzaghi consolidation theory was adopted to compute the hydraulic conductivity of bentonite/CaCO3 mixtures. The results demonstrated that the final swelling strain decreased with increasing vertical stress and the content of CaCO3 powders. The compression index decreased slightly with increasing CaCO3 content. It was found that as the CaCO3 content increased, the hydraulic conductivity of bentonite/CaCO3 mixtures decreased. There was a peak point in the shear strength of unsaturated samples with the differences of the CaCO3 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 CaCO3 powders filled pores of bentonite/CaCO3 mixtures and made the structure denser.