COMPRESSIVE STRENGTH OF RAPID SULFOALUMINATE CEMENT CONCRETE EXPOSED TO ELEVATED TEMPERATURES

The compressive strength, modulus and stress-strain behaviour of rapid-hardening sulfoaluminate cement concrete were evaluated as functions of the temperature increase. The compressive strength decreased from 51.3 to 31.1 MPa (around a 39 % reduction) as the temperature increased from 20 degrees C to 300 degrees C while the specimens burst at 400 degrees C before being removed from the furnace. A significant change in the stress-strain behaviour was noticed with an increasing temperature. For the control specimens (20 degrees C), linear elastic behaviour was followed by plastic defamation before reaching the peak stress prior to failure, but for higher temperatures, the modulus of elasticity was up to 85 % lower and was characterised by a gradually decreasing slope until failure. The micro-structural changes detected by SEM, DTG/TG and XRD were consistent with this pattern. The degree of cracking at the interfacial transition zone and crack-width growth detected by SEM followed a clear trend with the increasing temperature. The transformation of the primary hydration products (e.g., ettringite and AI(OH) 3 ) as detected by XRD and DTG/TG provides a useful explanation of the strength reduction with the increasing temperature up to 300 degrees C. The vapour pressure evolvement within the specimens at elevated temperatures correlates well with the reduced strength and modulus of elasticity, with a very intense effect at 400 degrees C.