Estimation of poromechanical and thermal conductivity properties of unsaturated isotropically microcracked cement pastes

This study focuses on the estimation of mechanical, hydromechanical and thermal conduction parameters of isotropic microcracked hydrated cement pastes in unsaturated conditions. The prediction of these parameters is obtained as a function of saturation degree and isotropic microcrack density parameter by applying an explicit effective medium approximation scheme on the basis of a simple microstructure description of the material. This latter is supposed to be composed of a homogeneous matrix in which are distributed ellipsoidal particles and penny-shaped inclusions representing pores and microcracks, respectively. These two types of inclusions are assumed to be of well-separated sizes so that a two-step homogenization procedure is employed. The effects of the pore shape and both open and close microcracks on the considered physical properties are investigated in partially saturated conditions by adopting a simplified desaturation-resaturation scenario. It is shown that the saturation degree repercussions on these properties increase when the pores have an oblate shape with low aspect ratio. Moreover, while Biot coefficient and thermal conductivity are significantly affected by saturation degree, undrained mechanical parameters appear to be only moderately modified by this factor. Besides, as expected microcracks induce important changes in all properties. The effects of the adsorbed water layers covering the surface of desaturated pores on the Biot coefficient are investigated by making use of the disjoining pressure concept, and results show only a moderate influence for very small pores. Copyright (C) 2010 John Wiley & Sons, Ltd.