Experimental Study On The Performance ECC-concrete Interface Adhesion And Resistance To(Salt) Freez-thaw

The engineered cementitious composites(ECC)has the advantages of multi-crack cracking and strain hardening,and much higher tensile strain comparing with that of ordinary concrete.The toughness and crack-control of the reinforced-concrete structure can improve by using ECC as a repair and reinforcement material,which can also effectively solve the problems of early cracking and poor ductility of concrete.For reinforced structures,the interface property between ECC and concrete is a weak area that deserves attention.At present,there are still many problems to solve in the research on the interface property between ECC and concrete in some alpine harsh environments.Therefore,this paper conducts experimental research on the bonding performance of the interface between ECC and concrete in erdinary and freeze-thaw environment.The main researches are as follows:(1)The resistance to(salt)freezing and the mechanical properties of PE-ECC,JPVA-ECC and CPVA-ECC after(salt)freeze-thaw cycles were studied.With the increase of the number of freeze-thaw cycles,the surface damage degree of the three ECCs increased,the dynamic elastic modulus decreased,the compressive strength decreased,and the ultimate elongation first increased and then decreased.After 300 water freeze-thaw cycles,the elastic modulus are all higher than 60%of their initial values,the mass increases,and the erosion damage and performance decline of salt freezing are much higher than those of the water freezing.The freeze-thaw resistance(salt)and mechanical properties of PE-ECC after freeze-thaw are better than those of JPVA-ECC and CPVA-ECC,the elongation rate after water freezing and salt freezing is basically above 8%and 3%,respectively.(2)The shear performance of the interface between ECC and concrete were studied through single shear tests on different factors,including ECC pouring process(post-cast ECC,prefabricated ECC),interface treatment,concrete compressive strength grade,ECC fiber type,and(salt)freeze-thaw cycles.The shear failure mode,bond-slip curve and shear strength of the interface between ECC and concrete in different influencing factors were obtained.The pouring process of ECC has basically no effect on the interface bonding performance,but the interface treatment method and the freeze-thaw cycle have a greater impact on the interface bonding performance.The high-pressure punching interface treatment method is more suitable for reinforced concrete structures,which can still maintain good interfacial bonding under the action.(3)The shear and flexural properties are studied through composite beam flexural tests on different factors,including the pouring process of ECC(post-casting ECC,prefabricated ECC),interface treatment method,concrete compressive strength grade,ECC fiber type,ECC layer thickness and ECC layer reinforcement parts(bottom,two sides,U-shaped)and(salt)freeze-thaw cycles.Some performance indexes are obtained,including the failure mode,load-deflection curve,load-strain curve and flexural strength of composite beams.Compared with ordinary concrete beams,the flexural strength and deflection of the composite beam improve greatly,the failure mode has been changed,and the cracks of concrete have been effectively controlled."U-shaped" composite beams are beneficial to protect the internal concrete and improve the(salt)freezing resistance of the composite beam.