Behavior and retrofit of heat-damaged reinforced concrete beams containing micro-silica and polypropylene

Heat-damaged reinforced concrete members can continue their service after proper retrofit. In this investigation, the performance of heat-damaged RC beams retrofitted by different methods such as the use of FRP and steel plates has been experimentally investigated. Eleven reinforced concrete beams, including beams containing micro-silica (MS) and polypropylene fibers (PPF), have been made. Two control specimens are tested at ambient temperature, and two similar beams are subjected to a temperature of 600 °C for an hour. To examine the strength, stiffness, and final displacement of the beams, four-point flexural test is carried out on the specimens. Then, seven other beams are heated and after cooling, they are retrofitted by different methods including CFRP sheet, steel plate jacket, and a combination of steel plate and FRP sheet. Four-point flexural test on the retrofitted beams is performed. The results of the non-retrofitted specimens showed that the beams made with micro-silica and PPFs had less strength reduction. The beam retrofitted with steel jackets is found to have the highest strength. In all specimens, the retrofit methods were able to compensate for the lost strength. However, FRP retrofit methods were not successful in restoring the initial stiffnesses. The failure mode of the beams after heating is changed from flexural to shear failure mode and even the retrofit methods were not able to compensate for this phenomenon.