Moisture and Heat Flow in Concrete Walls Exposed to Fire

Time-dependent distributions for temperature and moisture content in a concrete wall subjected to fire are determined by a model of heat and mass transfer in porous media. Free-water flow, bound-water diffusion, gas-phase flow, water-vapor diffusion, and thermal energy are accounted for in the model. The governing transient differential equations are discretized by a control-volume formulation reported by Patankar in (1980), and solved in time using a fully implicit scheme. Two different fire exposure curves (namely, standard curve according to ASTM E-119 and a more realistic curve reported by Ellingwood in 1991) are employed in the analysis. The assessment of two simplified models, in which all pore water is assumed to evaporate at 100°C, is performed by comparing their predictions to the full analysis. For temperature and saturation, the time developments predicted by the two simplified models and by the full analysis present similar trends; however, the simplified models seem to be appropriate only for very preliminary fire safety analyses, since they tend to underestimate temperatures.