Temperature Distribution in Early-Age Concrete Slabs Subjected to a Fire

This paper presents an investigation on the effect of real fire conditions on samples of early-age composite floor slabs, with profiled steel decking. When fires occur while a building is still under construction, composite slabs containing early-age concrete (less than 28 days) can be exposed to temperatures exceeding 900 °C. This can compromise the resistance of the composite slabs both immediately after the fire and after the subsequent curing period. Consequently, it is necessary for forensic engineers to understand the behaviour of the slabs under these fire conditions, and how heating will affect their resistance. This is especially important because decisions on whether to repair or replace the heated slabs are ultimately the responsibility of the engineer. To study the behaviour of the heated composite slab, samples were prepared and subjected to real fire conditions at 3 and 7 days following their concrete pour. The temperature distribution in the slab section was measured during the fire and cooling phases. The results were then compared against a two-dimensional finite-element model which had been validated against experimental data from previous studies. The model had close agreement with the experimental results for mature concrete in a standard fire. However, the comparison between the model and the experimental data from early-age concrete revealed discrepancies, suggesting that the ranges in parameters for modelling provided in the literature are not necessarily reliable for early-age concrete in real fire conditions.