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

Thermal conductivity X, water vapor permeability 8, and liquid moisture diffusivity kappa, 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 degreesC for 2 h, and loaded both mechanically and thermally. The values of lambda and kappa 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 lambda and as much as three orders of magnitude for kappa. In contrast, the values of 8 are found to increase by only about 40% compared to the basic unloaded material. It is proposed that the observed large differences in lambda and kappa are due to the formation of cracks and the increase of total pore volume, which were shown by visual analysis and mercury porosimetry. (C) 2003 Elsevier Science Ltd. All rights reserved.