Mass transport through concrete walls subjected to high temperature and gas pressure

The aim of this study is the modelling of mass transport phenomena through a concrete wall, when a gas (dry air plus water vapour) at high temperature and pressure is applied to one face of the wall. The temperature of the heated wall was increased from 20 to 141°C, while the other wall was exposed to ambient conditions. A uni-dimensional numerical analysis was performed, by using the thermohydromechanic model (THM) included in the Code_Aster for the description of non-saturated porous media. Two fluid phases were considered in the material: a liquid phase (water) and a gas phase (dry air plus vapour). The vapour-to-liquid phase change was introduced as well. Owing to the progressive saturation of the wall, the porosity, the shape of the sorption isotherm and the permeability greatly influenced the results. The numerical results are compared with experimental investigation. The tests concerned three concrete cylindrical specimens, which represented core samples extracted from a concrete wall. During the tests, the specimens were subjected to the same boundary conditions found in the wall (front end-section exposed to the autoclave and back end-section exposed to ambient temperature, and the lateral surface sealed and insulated to eliminate lateral hygral and thermal flux). Three different cementitious composites were tested (two concretes with different permeability for the first and second specimens, and one with highly porous mortar for the very permeable ‘flaw’ created in the third specimen). The numerical results were in good agreement with the tests in terms of phenomenological evolution and flow rate through the concrete, and confirmed the necessity of having reliable data on the thermal–hydromechanical properties of the material, to guarantee the validity of the results.