ABSTRACT
Abstract In cement-stabilized wastes that contain high amounts of sulfate, the U phase, a sodiumsubstituted AFm phase, is pointed out. This phase is shown to be responsible for the degradation of the simulated samples. Two types of expansion processes which lead to the degradation have been characterized: 1. secondary formation of the U phase, in samples C3S+C3A+Na2S04. 2. the U phase ~ ettringite transformation through leaching tests on samples C3S+U. The U phase, which is not detected in traditional cements, appeared as deleterious in our studied cement-stabilized wastes. Keywords: Cement-stabilized wastes, sodium sulfate, U phase, ettringite, expansion
1 Introduction
Among wastes produced by nuclear industry, liquids are the most important fraction by volume. Evaporation is widely applied to reduce their apparent volume, and it leads to solutions characterized by high concentrations of different salts. In some cases, the concentration of sodium sulfate may reach 200 to 250 giL. Large quantities of these wastes are solidified in cement matrices. It is necessary to investigate the behavior of this kind of cemented wastes because of the potential waste-binder interactions.
