Strength and durability recovery of fire-damaged concrete after post-fire-curing

The effect of post-fire-curing on the strength and durability recovery of f ire-damaged concrete was investigated. Twenty normal- (NSC) and high-streng th concrete (HSC) mixes incorporating different pozzolans. were prepared an d exposed to elevated temperatures till 800 degreesC. After natural cooling , the specimens were subjected to post-fire-curing in water and in a contro lled environment for a total duration of 56 days. Unstressed compressive st rength, rapid chloride diffusion, and mercury intrusion porosimetry (MIP) t ests were conducted to examine the changes in the macro- and microstructure of the concrete. The test results indicated that the post-fire-curing resu lts in substantial strength and durability recovery and its extent depend u pon the types of concrete, exposure temperature, method, and duration of re curing. In one case, the recovered strength was 93% of the original unfired strength. Scanning electron microscopy (SEM) investigations indicated that the recovery was due to a number of rehydration processes that regenerate the calcium-silicate-hydrate (C-S-H). The new rehydration products were sma ller in size than the original hydration products and filled the internal c racks, honey combs, and capillaries created during the fire. The surface cr ack widths were also reduced during the recuring process, and in most cases , they were found within the maximum limits specified by the American Concr ete Institute (ACI) building code. (C) 2001 Elsevier Science Ltd. All right s reserved.