Evaluating residual properties of thermally damaged concrete

Detailed observations are presented on the evaluation of the residual properties of high strength concrete specimens after exposure to high temperatures. The variables considered were fiber reinforcement consisting of steel or polypropylene microfibers and two different specimen sizes. Both heat treated and undamaged (no heat treatment) specimens were tested by conducting three-point bending experiments at ambient conditions approximately one month after exposure to the high temperature. Residual strength and post-peak response were monitored using a closed-loop load frame, and the damage zone was observed with optical and acoustic techniques. Electronic speckle interferometry provided high resolution measurements of the displacement field due to the development of fracture. The size and shape of the localized damage zone were identified through the acoustic emission due to pre-peak microcracking, one of the significant factors influencing the strength of quasi-brittle materials.