Reduction of water content in calcium aluminate cement with/out phosphate modification for alternative cementation technique

Abstract

Cementation of the secondary aqueous wastes from TEPCO Fukushima Daiichi Nuclear Power Plant is challenging due to the significant strontium content and radioactivity, leading to a potential risk of hydrogen gas generation via radiolysis of water content. The present study investigates the reduction of water content in calcium aluminate cement (CAC) with/out phosphate modification by a heat-treatment during the solidification. The reduction of water in the CAC was found restricted by the rapid formation of crystalline hydration phases, whereas the phosphate-modified system allowed the gradual reduction of water, achieving the reduction of 60% water content at 95 °C. Curing at 60–95 °C also eliminated the significant cracks found at 35 °C in the phosphate system. The possible difference in the amorphous products, NaCaPO₄∙nH₂O type at 35 °C and Ca(HPO₄)∙xH₂O type at 60–95 °C, may have contributed to the improvement in the microstructure together with the change in the pore size distribution.