A comprehensive study on post-fire curing of recycled aggregate concrete

The performance of recycled aggregate concrete after being post-fire cured was investigated. For this aim, three concrete mixes with 0, 50 %, and 100 % replacement percentages of coarse natural aggregate with coarse recycled aggregate were made. The temperature increased from room temperature with a speed of 10 °C /min, and the specimens were exposed to 400°C and 800°C. For comparison, some specimens were water re-cured, and some were tested without post-fire curing. Mechanical and durability tests, X-ray diffraction (XRD), and Scanning electron microscopy (SEM) were conducted. The results showed that after exposure to 400°C, the residual compressive and tensile strength of specimens containing recycled aggregate is improved. However, after exposure to 800°C, all properties of the specimens degraded significantly. After re-curing specimens exposed to 400°C, the properties of all specimens degraded, and as the replacement of natural with recycled aggregates increased, the specimens suffered a greater loss in mechanical properties. This was attributed to the low recovery potential as the main constituent of the cement matrix, calcium silicate hydrate, was still intact. After being exposed to 800°C and undergoing post-fire curing, specimens containing recycled aggregates showed greater recovery of their properties compared to normal concrete. This phenomenon was attributed to the dehydration of calcium silicate hydrates and cracking, which indicates a significant potential for the recovery of properties upon post-fire curing. The key factors were found to be cracks and dehydrated particles.