Experimental Study On Durability Of UHPC-NC Interface

Due to the vast territory and harsh natural environments,concrete structures will be damaged and destroyed to some extent.The safety and service life of damaged concrete structures can be effectively improved by means of reinforcement.Ultra-high performance concrete(UHPC)is known for its high strength,high toughness and durability,which makes UHPC be seen as a promising repairing material for normal concrete(NC).The research on the bonding performance of UHPC-NC is mainly focused on the conventional environment,and the research on the durability of UHPC-NC in harsh environment is relatively few.The bonding performance of UHPC-NC in harsh environment is one of the key factors affecting the reliability of UHPC in concrete reinforcement and repair engineering.Based on the above,the durability of UHPC-NC specimens in severe environment,including freeze-thaw cycles,dry-wet cycles,salt immersion and low temperature environment were studied in this paper.Through splitting tensile tests,the interfacial performance of UHPC-NC specimens under freeze-thaw cycles,dry-wet cycles and salt immersion were obtained.The results show that with the increase of the interface roughness,the resistance of the interface to freeze-thaw cycles increases but the resistance to chlorination decreases.The freeze-thaw cycling resistance of UHPC-NC is affected by NC strength and interface roughness.Based on this,a formula for calculating the tensile bonding strength of UHPC-NC is proposed.The shear properties of UHPC-NC were studied by two different interfacial shear strength tests.The UHPC-NC push-out test results indicate that relative displacement of bond strength increases and the bonding stiffness decreases with the increase of environmental test duration.According to the bond-slip curves obtained,the interface bond-slip model was established.The results of double shear test show that the low temperature resistance of interface agent itself is the key to restrict the bonding performance of UHPC-NC specimens.Compare the different test methods.The splitting tensile test is convenient and has good discreteness,but it is insensitive to interface roughness.The push-out test has good discreteness.But there is a lack of standard in push-out test.And thanks to the tiny thickness of UHPC,the construction of the specimens is difficult.The construction of double shear test is convenient,but the quality of specimen is hard to guarantee,which result in large discreteness.