Compressive strength of rapid sulfoaluminate cement concrete exposed to elevated temperatures

Abstract

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 °C to 300 °C while the specimens burst at 400 °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 °C), linear elastic behaviour was followed by plastic deformation 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 Al(OH)3) as detected by XRD and DTG/TG provides a useful explanation of the strength reduction with the increasing temperature up to 300 °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 °C.