Bentonite and concrete play an important role in the engineered barrier system of the near field nuclear waste repositories. In the construction of repositories a processing of materials to make them compatible may be required. Carbonation of concrete produces a decrease on concrete pH (pH~7 to 9), a sealing of cracks and a decrease of concrete permeability, avoiding the propagation of an alkaline plume towards other components of the barrier. Supercritical carbonation method can be completed in few hours, rendering it interesting as a treatment for reducing the concrete pH and enhancing several properties of cement based materials, such as the immobilization of hazardous wastes.
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