Residual Flexural Capacity Prediction in Heat-Affected Concrete Members through Ground Penetrating Radar and Thermal Imaging

Abstract Extreme fire and related heat exposure that is attributable to natural or man-made events may cause significant damage to concrete members, with associated strength reduction. Rapid and effective on-site post-fire assessment is essential in estimating the associated damage and loss of load carrying capacity, leading to decisions on rehabilitation or replacement. Current knowledge on this subject considers a single nondestructive evaluation (NDE) technique and only qualitative estimations of the damage or destructive methods such as coring. This study fills this critical knowledge gap through the experimental utilization of ground penetrating radar (GPR) and thermography techniques on laboratory heat-affected concrete beam samples. Parameters such as concrete strength, heat level and duration, and presence of fireproofing, steel, and fiber reinforced polymer rebars were considered through experimental design. The thermal imaging method was found to be successful in a qualitative way as supplementary to the more reliable GPR approach. Predictive quantitative models with high reliability relating the parameters to the expected GPR output amplitude and residual flexural capacity of beam samples were developed. User-friendly and rapid in-situ post-fire NDEs of concrete flexural members were proposed based on the availability of information on the considered parameters from as-built plans or actual observations.