Damage Mechanisms and Repairability of High Strength Concrete Exposed to Elevated Temperatures

Concrete has a good reputation for fire resistance because it has a low thermal conductivity and is non-combustible. However, concrete loses strength when exposed to elevated temperatures as a result of damage to the pore structure and chemical degradation. Strength and durability of concrete are lost when exposed to temperatures as low as 100 å¢å»C, even if it appears to be in-tact. Invasive repair techniques are often necessary to improve the durability and strength of the concrete due to limited information regarding high strength concrete under current guidelines. Rehydration is a promising alternative repair method, which can improve the microstructure of the concrete by hydrating previously unhydrated clinker in the fire damaged concrete. In addition, rehydration can save time and money, as well as minimize space lost, making it a financially attractive repair option. However, few studies have investigated the effectiveness of rehydration for the repair of high strength concrete, and relationships between the repair and damage mechanisms in high strength concrete are sparse. This work is intended to further the understanding of the behavior of concrete exposed to elevated temperatures, and the ability to repair that concrete, through the implementation of a comprehensive study. Using a multi-scale approach, the mechanisms by which concrete is damaged when exposed to elevated temperatures, and repaired using recuring, were established. Typical mix design variables were investigated to determine their influence on the extent of heat induced damage and viability of repair of the concrete. Based on this study, correlations were developed to estimate engineering properties of damaged and recured concrete, which can be used in the evaluation of the structure after a fire. Furthermore, recommendations regarding mix designs for future construction were provided to minimize the damage that would occur in concrete structures exposed to elevated temperatures.