Influence of curing condition for slag alkaline cement on it's microstructure and permeability of Cr⁶⁺

The influence of curing condition for slag alkaline cement on it's microstructure and the Cr⁶⁺ diffusivity through the pastes was investigated. Sodium silicate and sodium hydroxide have been used as alkaline activators. The slag alkaline cement pastes activated by sodium silicate and sodium hydroxide were cured at 25°C for 28d and at 105, 150 and 200°C for 12h by autoclave treatment. The ordinary portland cement has been used for comparing sample. The total pore volume decreased with increasing curing time and at higher curing temperature in all samples. The ordinary portland cement pastes cured at 25°C for 28d, the volume of pore with radii less than 5 nm had the largest. The slag alkaline cement pastes autoclaved at 105°C for 12h, the volume of pore with radii less than 5 nm had the largest. That volume of pore with radii less than 5 nm for alkaline cement pastes autoclaved at 105°C was larger than that of ordinary portland cement pastes cured at 25°C. The apparent diffusion coefficient of Cr⁶⁺ decreaesd linearly with increasing volume of pores with radii less than 5 nm and was determined by the volume of pores with radii less than 5 nm. The smallest apparent diffusion coefficient of Cr⁶⁺ of 7.0 × 10^-13 cm²/s was obtained for slag alkaline cement pastes autoclaved at 105°C for 12h with addition of sodium silicate as activator.