A drying and thermoelastic model for fast microwave heating of concrete

The use of high power microwaves to perform explosive spalling of surface concrete is a promising technique with applications in the area of concrete facilities decommissioning. The mechanism that creates explosive spalling is an interactive process of the thermal stress from high temperature gradients and the pore pressure generated from the water vaporization. In order to better predict the total stress distribution, the temperature has to be calculated by including the effect of water vaporization and water transport through a porous medium. In this paper, a one dimensional model solving the heat and diffusion equation for liquid and vapor phase with COMSOL finite element software is presented. The modelling of the drying process is based on the Spatial Reaction Engineering Approach (SREA developed by X.D. Chen). This paper discusses the influence of the relative energy activation parameter and effective diffusion coefficients on the temperature, water content and pore pressure in the case of fast microwave heating of concrete. This model is then used for a 3-D geometry with a sealed insulated concrete block and a conical antenna to compute the thermal stress, pore pressure and total stress.