The effect of chemical aging on water permeability of white cement mortars in the context of sol-gel science

In the sol-gel science, the influence of chemical aging on the fundamental water permeability remains open regarding to the durability performance of cement-based material. To reveal the pure effect of chemical aging, the water permeability and related micro-structural characteristics are measured on water-saturated mature mortars, whose aging is accelerated through heat treatment under water. It is found that, the chemical aging increases the volumetric porosity and coarsens the pore structure to a notable extent, which enlarge water permeability by 2.6-4.9 times. Based on the pore structure obtained through the low-field proton NMR technique, the water permeability is predicted by the Katz-Thompson theory with satisfactory accuracy, quantitatively confirming the direct effects of chemical aging on water permeability. Physically, because of the polymerization and rearrangement of C-S-H gel, cement mortars undergo substantial changes with enlarging radii for both interlayer and gel pores, slightly decreasing interlayer space but remarkably enlarging gel pore space.