Experimental Study On Effect Of Fire Extinguishing Method On Bond Behavior Between Concrete And CFRP Sheets

Concrete structures are frequently exposed to fire risk that causes deterioration in concrete materials’ mechanical properties;therefore,the concrete stiffness decreased and prone to collapse.Several rehabilitation/strengthening techniques have been used in recent years to prevent the failure of a concrete member that was exposed to fire.Among all strengthening methods,the most commonly used technique for repairing concrete members exposed to intense fire is to use carbon fiber reinforced polymer(CFRP)sheets.However,bond behavior between heat-damaged concrete and CFRP sheet has got less attention in previous studies.Therefore,this study was conducted to investigate the bond behavior between heat-damaged concrete and CFRP sheet through a double pull-out test.The experimental program consists of thirty-nine specimens,including three control specimens(un-burned)and thirty-six specimens burned at three different temperature degrees 200°C,400°C,and 600°C,with various times of exposure(i.e.,one and two hours).Two extinguishing methods were considered,air method and immersion method.The results show that as the temperature was raised,the bond strength increased until it reached 400°C,then which it significantly decreased at 600°C.Besides,bond strength was affected by the extinguishing methods;the water-cooling process showed a decrease in bond strength.The heat exposure period had a major impact on bond strength,with longer exposure times resulting in higher bond strength.This could be attributed to the epoxy penetrating the cracks that had appeared on the concrete surface.Moreover,an analytical study was performed to develop an analytical equation that predicts the bond strength between CFRP sheets and fire-damaged concrete.The proposed equation was developed using regression analysis and considers the effects of the extinguishing process,temperature degrees,and exposure times.Comparing the proposed equation’s results to those of the experimental equation demonstrates the proposed equation’s validity in predicting bond strength.Moreover,an analytical analysis was conducted in order to create an analytical equation that predicts the bond strength of CFRP sheets to firedamaged concrete.The proposed equation was created by regression analysis and takes into account the results of the extinguishing mechanism,temperature degrees,and exposure times.when the proposed equation’s effects are compared to those of the experimental equation,the proposed equation’s validity in estimating bond strength is shown.