Heat and mass transfer in heated concrete: evaluation and validation of five numerical models

Modeling concrete at elevated temperatures is essential to understanding the behavior of structural elements during fire, particularly with respect to spalling. To accurately predict temperatures and pore pressures, models must be validated against experimental data. However, most models in the literature focus on replicating experimental outcomes and often rely on input parameters sourced from the literature or determined by empirical tuning. To explore this further, a study of five models was conducted as part of the activities of the RILEM Technical Committee 256-SPF. On the theoretical side, state-of-the-art formulations are reviewed and similarities and differences between implementations are discussed. Using input parameters from various test reports, simulations of temperatures and pore pressures were performed and compared with test results for two types of concrete. While all of the models gave satisfactory results, they did so only when permeability values were applied that were significantly lower than those obtained from the standard tests. Since this trend was consistent across all models, it suggests that the permeability of concrete under heating conditions differs from that measured in standard material tests. As noted by some researchers, gas permeability in concrete is altered by the presence of water, probably due to swelling and rehydration. Identifying an accurate permeability value for these conditions remains an open research challenge.