Sorption and diffusion studies in cementitious grouts

Abstract

Laboratory experiments were conducted to evaluate the contaminant transport properties of cement-based sealing materials for use in vault sealing and fracture grouting within an underground repository for nuclear fuel waste. Diffusion coefficients were measured for tritiated water and 36Cl under simulated saline groundwater conditions for six mixtures of Sulphate Resistant Portland Cement and Silica Fume at two water to cement ratios. Tortuosity factors were calculated from the results of the diffusion tests and retardation factors for 137Cs and 85Sr were estimated from measured distribution coefficient, bulk density, and porosity values. The results of the diffusion experiments show both tritiated water and 36Cl to behave as reactive tracers in cement-based materials. The water to cement ratio was shown to have a significant effect on the retardation capabilities of the grout mixes with reatardation factors increasing as the water to solid ratio was reduced from 0.35 to 0.25. The results also showed the addition of silica fume to have impact on the potential migration rates of both 137Cs and 85Sr, however, under saline conditions, a similar reduction in the effective diffusion coefficients could be achieved through a decrease in the water to cement ratios.