Bending Strength of Composite Slabs Exposed to Fire at an Early Age

When fires occur during the construction of a building, concrete structural elements can be exposed to high temperatures while the concrete is still of early age (less than 28 days for normal concrete). This can compromise their resistance, due to a deterioration of mechanical properties. A review of the state of art revealed that, although numerous studies have been conducted on the residual strength of cured concrete subjected to high temperatures, there is a gap in the study of the residual strength of concrete slabs which were subjected to high temperatures from a compartment fire at an early age. The purpose of this study was therefore to evaluate the residual capacity in bending of concrete slabs that were subjected to fire when the concrete was only 3 and 7 days old. Consequently, data from actual fire tests were used to better understand the loss of bending strength. A theoretical model was developed to validate the residual bending resistance of composite slabs after exposure to fire. The experimental and theoretical results show that slabs subjected to a compartment fire at a young age have a reduced maximum bending capacity (at maturity, 28 days) in the order of 25–30% compared to the capacity of non-heated slabs.