WATER PERMEABILITY AND CHLORIDE-ION DIFFUSION IN PORTLAND-CEMENT MORTARS - RELATIONSHIP TO SAND CONTENT AND CRITICAL PORE DIAMETER

The pore structure of hydrated cement in mortar and concrete is quite different from that of neat cement paste. The porous transition zones formed at the aggregate-paste interfaces affect the pore size distribu tion. The effect of the sand content on the development of pore struct ure, the permeability to water, and the diffusivity of chloride ions w as studied on portland cement mortars. Mortars of two water-to-cement ratios and three sand volume fractions were cast together with pastes and tested at degrees of hydration ranging from 45 to 70%. An electric ally-accelerated concentration cell test was used to determine the coe fficient of chloride ion diffusion while a high pressure permeability cell was employed to assess liquid permeability. The coefficient of ch loride ion diffusion varied linearly with the critical pore radius as determined by mercury intrusion porosimetry while permeability was fou nd to follow a power-law relationship vs. this critical radius. The da ta set provides an opportunity to directly examine the application of the Katz-Thompson relationship to cement-based materials.