IMPACT OF CURING TEMPERATURE ON THE SATURATED LIQUID PERMEABILITY OF SALTSTONE

This report focuses on the impact of curing temperature on the performance properties of simulated Saltstone mixes. The key performance property of interest is saturated liquid permeability (measured as hydraulic conductivity), an input to the Performance Assessment (PA) modeling for the Saltstone Disposal Facility (SDF). Therefore, the current study was performed to measure the dependence of saturated hydraulic conductivity on curing temperature of Saltstone mixes, to correlate these results with measurements of Young's moduli on the same samples and to compare the Scanning Electron Microscopy (SEM) images of the microstructure at each curing temperature in an effort to associate this significant changes in permeability with changes in microstructure. This work demonstrated that the saturated liquid permeability of Saltstone mixes depends significantly on the curing temperature. As the curing temperature increases, the hydraulic conductivity can increase over three orders of magnitude from roughly 10{sup -9} cm/sec to 10{sup -6} cm/sec over the temperature range of 20 C to 80 C. Although an increased aluminate concentration (at 0.22 M) in the ARP/MCU waste stream improves (decreases) saturated permeability for samples cured at lower temperatures, the permeabilities for samples cured at 60 C to 80 C are the same as the permeabilities measured for an equivalent mix but with lower aluminate concentration. Furthermore, it was demonstrated that the unsaturated flow apparatus (UFA) system can be used to measure hydraulic conductivity of Saltstone samples. The permeability results obtained using the UFA centrifuge system were equivalent within experimental error to the conventional permeameter results (the falling head method) obtained at MACTEC. In particular the UFA technique is best suited for the range of hydraulic conductivities between 10{sup -10} cm/sec to 10{sup -6} cm/sec. Measurements of dynamic Young's moduli (E) for these mixes revealed a correlation between E and hydraulic conductivity. Therefore, it is possible to use E values to estimate the values of hydraulic conductivity. Measurement of Young's modulus is much easier than the measurement of permeability of Saltstone mixes and facilitates the measurement of the time dependence hydraulic conductivity. The results presented in this report show that changes in permeability as a function of curing temperature appear to be related to microstructural changes in the cured Saltstone mixes. Backscattered electron microscopy images revealed significant differences between the samples cured at different temperatures