Modification of calcium aluminate cement with phosphate for incorporation of strontium chloride

Large quantities of aqueous secondary waste are generated from the processing of contaminated water after the nu-clear accident in Japan. Cementation of these wastes is challenging because their significant radioactivity may cause the radiolysis of water contents in cement, posing a risk of hydrogen gas generation. The application of calcium aluminate cement modified with phosphates (CAP), as an alternative cementing system, is interesting because this system is based on acid-base reaction, and its water content can be reduced by mild heating once the system is mixed. The present study focused in the use of Secar 71, a calcium aluminate cement with a high alumina and low silica compositions, and its effects of on the production of CAP system at elevated temperatures. The modification of Secar 71 with phosphates was successful, and the reduction of water content by about 35% was achieved in the CAP system containing SrCl2 after curing the system at 80°C for 7 days. The micro cracks, typically observed in the CAP system cured at lower temperature, was significantly reduced by curing at 80°C. The obtained results show a potential of Secar 71 to prepare CAP for cementation of aqueous secondary wastes.