Enhancing the residual performance of concrete using calcium aluminate cement composites

Fire events severely affect reinforced concrete members, with spalling owing to fire being a critical challenge that can be minimised but not eliminated. Ordinary Portland cement (OPC), the most common concrete binder, performs poorly at elevated temperatures. With the aim of improving fire resistance, the potential of calcium aluminate cement (CAC) combined with various fibres was investigated in this study. To this end, 16 concrete mixes were prepared, replacing OPC with different percentages of CAC and using polypropylene fibres (PPF), steel fibres (SF) and hybrid fibres (PPF and SF) as reinforcement. Specimens were subjected to elevated temperatures (200–800°C) and cooled in either ambient air or by controlled water quenching. The colour change, crack widths, mass loss and non-destructive test results (rebound hammer and ultrasonic pulse velocity) were monitored. The residual compressive strength of the specimens was evaluated after destructive testing, and selected samples were also analysed using X-ray diffraction to understand the microstructure and chemical changes in concrete owing to high-temperature exposure. Although the CAC mixes exhibited slightly lower initial strength than the OPC mixes, they demonstrated superior strength retention (by about 30%) and spalling resistance at high temperatures, particularly with the combined effect of fibres and the managed cooling strategies. This study underlines the promising synergy of CAC and fibres for significantly improving the performance of concrete after exposure to elevated temperature.