Magnesium-Phosphate Cement Pastes to Encapsulate Industrial Waste Powders

Although Ordinary Portland Cement (OPC) is the main cement considered in relation to industrial and radioactive waste management (as being the most widely used in the world), several waste types are incompatible with OPC. In particular, magnesium potassium phosphate cements (MKPC) are more suited to some waste types. They are promising durable alternatives to OPC cements, owing to their fast and adjustable setting time and to a high compressive strength on the short term. However, in stoichiometric proportions (Mg/P = 1), MKPC pastes swell significantly. Swelling decreases with increasing (Mg/P), i.e. with increasing content in over-stoichiometric MgO. In the context of hazardous waste management, our idea is to incorporate as much of powdered waste as possible, in replacement to over-stoichiometric MgO. The adequate granulometry and nature of powders, suitable with MKPC, need to be determined. Therefore, in this research, in MKPC pastes, over-stœchiometric MgO is replaced by fillers of varying nature and granulometry (fineness). First results explain the phenomena and phase formation, responsible for MKPC swelling, and how this is avoided when adding adequate powders. The most adapted filler, which removes swelling and allows sufficient spread, is described, as well as the threshold mass ratio of fines/cement (F/C), above which swelling of stœchiometric MKPC cement is eliminated.