The effect of compressive stress on thermal and hygric properties of Portland cement mortar in wide temperature and moisture ranges

Basic thermal and hygric parameters of cement mortar — namely, the thermal conductivity, the linear thermal and hygric expansion coefficients, moisture diffusivity, and water vapor permeability — are determined in dependence on the applied mechanical load inducing compressive stress in the samples ranging from 0% to 90% of compressive strength. The measurements are performed in wide temperature and moisture ranges, from 20°C to 1000°C and from the dry state to the saturation water content. The measured results show that both thermal and hygric parameters of cement mortar are affected only by compressive stress of 90% of the compressive strength of the material and higher, in a significant way. Scanning electron microscope images and porosimetric measurements reveal that the most probable reason for the observed differences in thermal and hygric parameters is the appearance of cracks with a typical width of 1–2 μm.