Thermal and hygric properties of Portland cement mortar after high-temperature exposure combined with compressive stress

Thermal conductivity λ, water vapor permeability δ, and liquid moisture diffusivity κ of cement mortar are measured on specimens subjected to four types of pretreatment, namely, unloaded, mechanically loaded to 90% of compressive strength, thermally loaded by subjecting to a temperature of 800 °C for 2 h, and loaded both mechanically and thermally. The values of λ and κ are found to depend very significantly on the loading mode. The maximum differences observed compared to the unloaded samples are almost one order of magnitude for λ and as much as three orders of magnitude for κ. In contrast, the values of δ are found to increase by only about 40% compared to the basic unloaded material. It is proposed that the observed large differences in λ and κ are due to the formation of cracks and the increase of total pore volume, which were shown by visual analysis and mercury porosimetry.