Chemistry and Performance of Blended Cements and Backfills for use in Radioactive Waste Disposal

ABSTRACTThe ability of NaCl and MgSO4 to impair the performance of Portland cement, blended cements containing slag and fly ash and of a permeable backfill have been measured. Performance is determined by decrease in pH, changes in mineralogy and loss of physical coherence. Experiments have been made at 25°, 55° and 85°C and extensively backed up by chemical models of cement performance. NaCl, up to 1.5M, has a comparatively slight impact on performance but MgSO4 rapidly and almost quantitatively reacts, lowering system pH's to < 10, conditioned by mixtures of Mg(OH)2 and magnesium silicates with gypsum.