Dependence of unsaturated chloride diffusion on the pore structure in cementitious materials.

Conceptual analysis is performed to examine the effects of pore features on the water continuity in unsaturated porous systems. The roles of pore features in relative chloride diffusion coefficient (D rc) of mortar specimens at various degrees of water saturation (S w) were studied based on mercury intrusion porosimetry and resistivity tests. It is found that the role of pore structure in the D rc - S w relationship is a result of its effect on the water continuity. Porosity and tortuosity are not relevant to the D rc - S w relationship. A finer pore size distribution or lower pore connectivity tends to result in a lower D rc. The pore size effect on the D rc is pronounced primarily at high S w , while the D rc is dominated by the pore connectivity at low S w. Cement mortar with a higher water-to-binder ratio shows larger chloride diffusion at high relative humidity levels but smaller chloride diffusion at low relative humidity levels. [ABSTRACT FROM AUTHOR]