High-Temperature Residual Strength and Microstructure in Air-Entrained High-Strength Concrete

Use of high-strength concrete (HSC) in built infrastructure allows efficient structural systems with higher strength and durability. However, HSC being sensitive to high temperatures results in reduced residual strength after fire exposure, which impairs post-fire structural serviceability. This lower performance of HSC results from its characteristic dense microstructure that prohibits dissipation of pore pressure at high temperatures. Under fire conditions, similar to sublimation (melting) of polypropylene fibers in HSC, air entrainment can reduce microstructural damage by allowing dissipation of vapor pressure. In this study, residual mechanical and physical properties of air-entrained HSC (AEH) were investigated after exposure to high temperatures up to 800 degrees C (1472 degrees F). Residual mechanical properties comprised of compressive and splitting tensile strength, stress-strain response, elastic modulus, and changes in physical properties consisted of mass loss, cracking behavior, and microstructural changes. Results show that AEH retains better residual mechanical properties after exposure to high temperatures; however, a higher air content proved less beneficial.