Coupled heat and moisture transport in concrete at elevated temperatures - Effects of capillary pressure and adsorbed water

The importance of capillary pressure and adsorbed water in the behavior of heat and moisture transport in concrete exposed to high temperatures is explored by incorporating their behavior explicitly into a computational model. The inclusion of these two phenomena is realized with a formulation of a modified model, which represents an extension to the significant work of Tenchev et al. Comparative studies were carried out, using a benchmark problem, and it was determined that while the Tenchev formulation underestimated the capacity for fluid transport in the concrete, resulting in an overprediction of pore pressures ( which may affect the prediction of mechanical damage and spalling), the inclusion of capillary pressure had little effect on the results. More important was the accurate representation of the free water flux, which has a significant effect on the prediction of vapor content and subsequently pore pressure. It was furthermore found that, while the adsorbed water flux may be minimal when concrete is exposed to high temperature, its presence has a significant effect on the fluid transport behavior and the prediction of pore pressures.