Influence of post-fire recuring regimes on the properties of self-compacting concrete with heavyweight aggregate

Fire safety is essential in construction, as accidental fires subject concrete structures to high temperatures that result in significant damage. This study examines the development of self-compacting concrete (SCC) characteristics with barite heavyweight aggregate (20-100% substitution of natural coarse aggregate) after being exposed to 600 °C, followed by several post-fire re-curing methods (water, CO₂, water-glass, and air). The property evolution was examined for cracking, density loss, residual compressive strength, and ultrasonic behavior, verified by FTIR, MIP, and SEM-EDX tests. The exposure to 600 °C resulted in widespread microcracking, significant mass loss, and decreased strength, besides the severity increasing with higher barite concentrations due to the brittleness and thermal sensitivity of heavyweight aggregate. Post-fire curing demonstrated specific recovery mechanisms: water curing promoted rehydration and achieved partial strength recovery of approximately 75% of pre-fire values; CO₂ curing improved densification via carbonation but resulted in increased brittleness; water-glass curing partially filled cracks but decreased long-term stability; and air curing caused additional drying shrinkage and further deterioration. The results highlight the interrelated chemical and microstructural changes that influence the post-fire development of SCC characteristics, revealing that water and CO₂ re-curing are the most effective methods for performance restoration.