Concrete Damage and Spalling Monitoring in Fire Tests via Ultrasonic Pulse-Echo and Ground-Penetrating Radar

Spalling in concrete during fire still needs to be fully understood, since the complex interaction of different aspects, such as pore pressure, thermal and load-induced stresses, as well as material physico-mechanical damage and heating rate, makes difficult the comprehension of the mechanisms behind this phenomenon. Within this context, monitoring the progress of spalling and moisture migration during heating is a challenging task, being most of the available techniques hardly suitable for the implementation in the test furnace. Among the Real-Time survey techniques, promising results were obtained from Ultrasonic Pulse-Echo (UPE) and Ground-Penetrating Radar (GPR), both based on the evaluation of the echo delay and attenuation of the waves reflected by the specimen side exposed to fire. UPE and GPR were implemented in the case of fire tests performed on concrete slabs subjected to heating at the bottom face, and the results are discussed in the present paper.