Influence of FRP Repair on the Axial Behavior of Fire Damaged Concrete

The exposure of concrete to elevated temperatures detrimentally affects its mechanical properties and thus, efficient repair materials and schemes would be needed to regain these properties. This study reports the results of an experimental work on the influence of fiber reinforced polymer (FRP) repair on the axial stress–strain behavior of concrete cylinders exposed to fire. Within the scope of the study, twelve plain concrete cylinders with dimensions of 150×300 mm were cast. While three of the cylinders were kept in ambient conditions, nine of them were exposed to ISO-834 standard fire for 60 minutes. After natural cooling, i) three of the fire exposed specimens were kept without repair, ii) three of them were repaired by jacketing with two layers of carbon FRP sheets and iii) other three of specimens were jacketed with four layers of FRP sheets. Then, all of the specimens were tested under uniaxial compression. The test results indicated that exposure to elevated temperatures leads to a reduction in compressive strength and modulus of elasticity but an increase in the axial strain corresponding to peak stress for the heated plain specimens. When confined with FRP jackets, the compressive strength and deformation capacity of these fire damaged specimens enhanced remarkably. On the other hand, the repair technique was found to be ineffective on reinstating the axial stiffness of the specimens which was reduced after fire exposure. Furthermore, the prediction performance of a unique model available in the literature that has been proposed for predicting the axial stressstrain behavior of fire damaged FRP confined circular columns was investigated. It was seen that the model did not exhibit a reasonable performance for the specimens tested in this study.