Experimental Methods for Spalling Monitoring During and After a Fire

Monitoring the progress of spalling and moisture front in concrete elements subjected to heating is a challenging task, since most of the available techniques can be hardly implemented in the test furnace. This is a critical issue, because the measurement of temperature and pressure can be not sufficient to define the conditions for spalling if depth and area involved, as well as occurrence time are not known. Generally speaking, monitoring can be performed by means of Real-Time or Post-Event survey. As concerns the former approach, promising results are expected to come from ultrasonic Pulse-Echo and Ground-Penetrating Radar methods, both based on the measurement of the time delay of (ultrasonic and electromagnetic, respectively) echoes reflected by the specimen side exposed to fire. Other methods for Real-Time monitoring can be Digital Image Processing of pictures taken during heating, and Acoustic Emission. As regards spalling survey after fire, laser profilometry, optical size measurement and weighing of the collected splinters can be co-ordinately used to depict some statistical trends of the fracture process due to fire. These methods (except Acoustic Emission) have been – or will be – 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.