Time Depndence of pH in a Cementitious Repository

Abstract

ABSTRACTThe pH of a cementitious radioactive waste repository is expected to decrease with time as water leaches out soluble ions or as a result of reactions between repository constituents. These processes have been simulated in the laboratory and the results compared with behaviour anticipated from the known chemistry of cement compounds.The studies indicate that the pH in Portland cements and Blast Furnace Slag cements (BFS) is likely to remain above 10.5 for very long periods of time, of the order of several hundred thousand years for a typical repository. They also show that extensive use of Pulverized Fuel Ash (PFA) leads to uncertainty in long term pH which could be as low as 9 to 10 in some cases.