Experimental Study On Evolution Law Of Epoxy Mortar-concrete Interface Performance In Cold Region

China is rich in water resources,and there are a large number of water conservancy projects under construction and completed.However,due to the influence of the natural environment,service conditions and operation characteristics of the hydraulic concrete structure,there are many problems such as damage and destruction after a certain period of service.In order to realize the better operation and give full play to its service benefit,it is very necessary to reinforcement and repair it at the initial stage of damage.Because of its high strength,good toughness,excellent durability and corrosion resistance,low temperature epoxy mortar can be used in hydraulic concrete structure repair engineering.In the process of repairing concrete in cold area,the interface between epoxy mortar and concrete belongs to the weak area of repairing structure.Therefore,this paper used universal testing machine to carry out compression test and flexural test on epoxy mortar solidified at low temperature and undergo freeze-thaw cycle,and studied the mechanical properties and frost resistance durability of epoxy mortar solidified at low temperature.Through shear strength test and splitting tensile test,the influence of curing temperature,water content of substrate concrete and interface roughness on the interface bond strength of epoxy mortar-substrate concrete composite specimen was studied,and the failure mode of interface was analyzed.Through rapid freeze-thaw test,the influence of water content and curing temperature on the interface frost resistance durability was studied.At the same time,analyzed the interface microstructure,and the effects of water content and curing temperature on the interface microstructure with the scanning electron microscope.The conclusions are as follows:(1)The epoxy mortar had good frost resistance and durability.After 300 freeze-thaw cycles,the mass and relative dynamic modulus of elasticity had no obvious change.The flexural strength decreased by 29.63%,and the compressive strength only decreased by 9.32%.(2)The epoxy mortar had good early strength performance,and the compressive strength could reach 91.62% of the 28 d compressive strength after curing at room temperature(20℃)for 7d.With the decreased of curing temperature,the compressive strength decreased.The compressive strength could reach 104.9 MPa after curing at 20℃ for 7d,and only 3.0 MPa after curing at-20℃.(3)With the substrate concrete water content increased,the splitting tensile strength and shear strength of the interface gradually decreased,and the failure mode of the interface gradually changed from the cohesive failure mode of the substrate concrete to the mixed failure mode.With the increased of substrate concrete interface roughness,the splitting tensile strength and shear strength first increased and then decreased,and the optimal bonding roughness was2.75 mm.With the decreased of curing temperature,the interfacial splitting tensile strength and shear strength of composite specimens decreased gradually.(4)With the freeze-thaw cycles increased,the interfacial shear strength of composite specimens decreased gradually.The substrate concrete water content higher,the more serious the damage of interface deterioration caused by freeze-thaw cycles.Under the condition of saturated water content(3.89%),the shear strength of interface decreased by 60% after 200freeze-thaw cycles.Due to the phenomenon of "freeze-thaw detachment",there were mainly occur the interface failure mode.(5)Through micro analysis,it was found that the lower the curing temperature is,the more internal pores and cracks are,the wider the interface crack is,and the worse the bonding effect is.The interfacial moisture would lead to the destruction of the molecular structure of epoxy resin,resulting in adverse deformation,porous structure and bond strength reduction.In this paper,the mechanical test and theoretical analysis were used to study the mechanical properties of epoxy mortar-concrete interface in low temperature environment.The research results were of great significance for the application of low temperature epoxy mortar in the repair of hydraulic concrete structure in cold areas,and provide reference for the design and repair of structure.