HEAT AND MOISTURE TRANSFER IN CONCRETE SLABS

To predict the moisture distribution in concrete slabs as functions of time, the dependence on the relevant material characteristics must be considered. The phenomena relevant for moisture, pressure, and temperature distribution are coupled. A diffusion theory with a linear or a nonlinear coefficient of diffusivity is not adequate for the description of the drying behavior of hardening concrete. A general mathematical description for the system has to be based upon a non-equilibrium, irreversible flow of heat and moisture. The distribution of pore size may be considered to be the most important parameter affecting moisture transfer in a porous medium. Based upon mass and energy transfer processes and on the liquid-vapor equilibria, a set of governing differential equations is developed for simultaneous heat and mass transfer during the pendular state of drying. Numerical examples, using the theory developed, are illustrated for natural drying of concrete slabs. They show that during the pendular state of drying, both diffusion and evaporation-condensation mechanisms are the governing processes in drying. © 1979.