Influence of CFRP Confinement on Bond Behavior of Steel Bars Embedded in Concrete Exposed to Elevated Temperatures

This study is presented in two parts. The first part reports the results of an experimental study where the axial capacity of fire-damaged specimens repaired by expansive cement concrete and CFRP wrap were investigated. Specimens were subjected to axial compressive loading and their resulting stress-strain curves were recorded. The cross section for some of the specimens were changed from square to circle shape. To modify the shape, expansive cement concrete has been utilized to fill the gap between the circular and the square cross sections. The test results indicated that heating the specimens up to 500°C caused a severe decline in compressive strength and the elastic modulus of concrete. Two layers of CFRP wrap around the concrete not only compensated the drop in compressive strength but furthermore it increased the strength beyond that of unheated specimen. After heating the square specimens, that were first subjected to shape modification and then wrapped by CFRP sheet, experienced increase in the strength and the elastic modulus. Therefore, the stiffness and the compression strength of fire-damaged square concrete specimens could be compensated fully by the use of shape modification and the CFRP wrapping of the cross section. The second part of the thesis has comprehensively studied the effectiveness of strengthening with CFRP wrapping for maintenance of bond behavior between bar and heat-damaged concrete. The effects of temperature (room temperature as reference, 200°C, 400°C, 600°C and 800°C), concrete cover (25 mm and 35 mm), concrete compressive strength (30 MPa and 40 MPa) and CFRP sheets have been investigated by performing bond test. The results show that strengthening with CFRP can effectively increase the bond strength of samples subjected to high temperature and also can change the failure mode from brittle to a more ductile one. Moreover, the mechanical properties decreased as the temperature increased, especially after 400°C, so that at 800°C, the compressive strength reduces to around 80%. It was observed that exposure to heat reduced the concrete-bar bond strength particularly for samples with thicker cover and higher compressive strength. But confinement with CFRP improved the bond strength significantly and this was particularly true for samples exposed to high temperature. The effectiveness of wrapped were more significant for samples with low compressive strength and thin concrete cover.