IDD prediction model of thermal conductivity of wet cement mortar with mixed defects of cavities and cracks

Cement mortar is prone to product defects after pouring, curing, and loading, which will significantly change its thermal conductivity. Thermal conductivity of mortar varies with the change of internal moisture in different humidity environment. The defects in cement mortar were divided into two basic types of cavities and cracks. Assuming that water and air with different volume fractions only exist in the defects, there were equivalent to homogeneous medium inclusions using serial method, and then randomly embedded into the dry mortar matrix. Based on the Interaction Direct Deduction (IDD) estimation method, the prediction model of equivalent thermal conductivity of cement mortar with different saturation degrees when cavities and cracks exist alone or simultaneously was established. The influence function of crack random distribution was put forward to improve the prediction accuracy. The rationality of the prediction model was verified by comparison with the numerical simulation results, and many discussions were proposed. The results show that when the saturation degree is constant, the thermal conductivity of mortar gradually decreases with the increasing of defect content and the content ratio of cavities to total defects. When the defect content is constant, the thermal conductivity tends to increase with the increasing of saturation degree, but when the saturation degree is small, the influence of saturation degree is smaller than that of defects. When the saturation degree reaches a certain value, it’s the influence become greater than that of defect content. The predicted model proposed has a clear physical basis and simple form, which is convenient for engineering application. It can provide theoretical support for the study of equivalent thermal conductivity of cement-based materials with certain damage, and can also provide reference for the study of thermal conductivity of composites materials with linear shaped inclusions and spherical inclusions.