Next: References Up: Main Previous: Results and Discussion
Chloride diffusion and water permeability in pastes and mortars with different sand contents were investigated using a concentration cell with a limited electrical gradient and a high pressure permeability cell. The coefficients of diffusion were calculated from a modified version of Fick's second law. It can be concluded that:
1. The method yielded the diffusion coefficients in a relatively short period (up to 10 days) with acceptable variability of 4 to 7%.
2. The diffusivity and permeability of both pastes and mortars decrease with increasing degree of hydration, the rate of hydration being different for pastes and mortars.
3. Increasing the w/c ratio reduced the resistance of both pastes and mortars to Cl− diffusion and water flow.
4. For the same degree of hydration, introducing sand particles into the cement paste resulted in higher transport coefficients.
5. A good linear relationship between the coefficient of diffusion and the critical pore radius, as determined by MIP, was observed. A power-law relationship with an exponent of 3.3 was observed in relating permeability to this same critical pore radius.
6. The Katz-Thompson relationship appears to have limited validity for cement-based materials, providing accurate estimates of permeability at w/c=0.5 but significantly overestimating the permeability for the more hydrated w/c=0.4 systems; this suggests that the Katz-Thompson relation may work better for systems with interconnected capillary pore networks, than for systems where the gel pores dominate the transport.