THE U-PHASE-FORMATION IN CEMENT-BASED SYSTEMS CONTAINING HIGH AMOUNTSOF NA2SO4

Simulated cemented low level wastes containing high amounts of Na2SO4 (10 similar to 15%) were examined with respect to the mineralogy of th e solid phases, chemical composition of the interstitial aqueous phase and immersion behaviour in water. All results reveal the formation of a mineral called U phase, first observed by Dosch and zur Strassen in 1967, and its deleterious effects on the samples immersed in water. I t appears that this phase can form only at very high alkaline concentr ation, not compatible with traditional cement paste. Two possible degr adation mechanisms associated with the U phase are proposed which are to be elucidated in further works.