Behavior Of Concrete To Concrete Interface Under Direct Tensile Static And Fatigue Loading

The concrete to concrete interface bond strength is very important to ensure the overall performance of concrete composite members.The main factor in the performance of concrete repairs is the good bond strength between new concrete(overlay)and old concrete(substrate).An experimental study conducted on twenty-one concrete specimens to investigate the behavior of concrete to concrete interface under direct tensile static and fatigue tests.Several parameters were investigated.These parameters include: using different types of fibers such as steel fiber(SF),polypropylene fiber(PPF)and steel with polypropylene fibers,three types of surface roughness techniques which were surface partially chipped(D),brushing surface(B),hand brush and grooving surface(BG),and mechanical grooving surface(MG),three different compressive strength with a value of 40 MPa,50MPa,and 60 MPa,and three interfacial bond angle of 45°,60°,and 90°.Digital Image Correlation(DIC)technique was used to monitor and track the strain distribution and surface displacement of each test specimen.The experimental results indicated that the contribution of fibers on the bond strength of concrete to concrete is significant and mainly depends on the types of fiber being used.Therefore,three types of failure were observed in this study and these failures are bond failure,interface failure with partially substrate failure and overlaid failure.The failure mode of concrete specimens reinforced with fibers was better than those of plain concrete.Therefore,the bond strength of specimens reinforced with fibers was significantly improved compared to those of the plain concrete.The chiseling specimen(D)recorded the highest value of tensile bond strength compared to other surface roughness techniques.The use of different compressive strength has a slight effect on bond strength.The effect of interfacial surface angle on the tensile bond strength can be clearly observed;in the 45° angle,the tensile bond strength was the highest followed by that with an angle of 60°,while the specimen with an angle of 90° failed even before starting the test,which reflects the importance of the interfacial bond angle in increasing the tensile bond strength.Furthermore,experimental results show that the specimens reinforced with fibers have better withstand fatigue life and bond strength compared to the plain concrete specimen due to the fiber bridging effect.Two fatigue life equations were proposed based on the collected database to determine the maximum stress level of plain concrete and steel fiber concrete.These proposed equations were compared with other equations proposed by other researchers and provided more reasonable and accurate results than the results obtained from researcher equation.