Degradation of Transport Properties in Self-Compacting Concrete Under Thermal Stress

Self-compacting concrete (SCC) has emerged as a material that enhances workability and exhibits mechanical performance comparable to conventional concrete. This aspect of SCC may help restore strength and durability, the critical parameters for effective rehabilitation and reusability, after a structure is exposed to fire. However, beyond mechanical strength, SCC must also meet durability requirements, particularly regarding its transport properties. The presented study investigates the impact of elevated temperatures on the transport properties of SCC. The study examines the changes in transport properties, such as water sorptivity, air permeability, and chloride migration, before and after exposure to high temperatures (300°C, 500°C, 800°C) for variable exposure time (60 min. and 120 min.) and cooling techniques (ambient air cooling and water spraying). In addition, the mechanical properties of SCC, such as compressive strength and mass loss, were evaluated. The results indicate significant degradation in transport properties as compared to compressive strength. Degradation in the transport properties started at 300°C. Among all transport properties, the air permeability showed the highest sensitivity, and maximum degradation occurred at this temperature. Although mechanical properties also declined, their deterioration was less pronounced than that of the transport properties; a significant degradation occurred after 300°C. Notably, extending the exposure duration from 60 to 120 minutes had a relatively minor impact, whereas the use of water quenching as a cooling method further intensified the degradation, likely due to the effects of thermal shock over normal cooling. Scanning electron microscopy (SEM) analysis was also conducted to check the microstructure of the SCC after fire exposure.