Study On The Interfacial Performance Between Composite Reinforcement Layer And Concrete & The Flexural Behavior Of RC Beams Strengthened With PCM-FRP Grid

China is a large country of reinforced concrete(RC)structures widely used in towns,transportation,and national defense.With the increase in the using time of these structures,the transformation of the use function,and the impact of natural disasters such as earthquakes and typhoons,it is necessary to strengthen them.Fiber Reinforced Polymer(FRP)has been widely favored since its inception.Due to its light weight,high strength and other characteristics,FRP materials have been gradually applied in the field of reinforcement.However,with the aging of adhesive epoxy resin and poor shear resistance in actual reinforcement,the performance of FRP utilization rate is low,so that the damaged structure is far from the expected reinforcement effect,and FRP material is wasted at last.Polymer cement mortar(PCM)spraying technology uses modified cement mortar as a binder to replace epoxy resin,and takes FRP profiles(such as FRP mesh)as a reinforcement material.This kind of reinforcement makes FRP and concrete as a whole,to improve some of the shortcomings of epoxy resin,being a new type of reinforcement that has only appeared in recent years.Therefore,this paper aims to clarify the feasibility of the PCM-FRP grid reinforcement method,explore the effect of PCM-FRP grid reinforcement on reinforced concrete structure,study the mechanical behavior of interface between PCM-FRP mesh and concrete,and research the flexural behavior of reinforced concrete beams.The main works have been taken as follows:1)Sorting out the 15 single-shear adhesive performance tests,which is about PCM-FRP grid reinforced concrete test block,carried out by the research group.From the perspective of the amount of grid unit reinforcement,analyzing the interface failure form of the specimen and the vertical strain of the grid.The peel failure energy of each specimen was calculated by using the bond slip curve and the formula was summarized.The research results show that:the interface damage degree of the single-shear specimen is positively related to the unit reinforcement,and the proposed formula for peeling failure energy can accurately calculate the interface peeling failure energy corresponding to the unit reinforcement of FRP grid;2)Five concrete beams strengthened with PCM-FRP grids were proposed.Focusing on the influence of the flexural performance about the number of grid layers and the amount of grid unit reinforcement.The unit reinforcement of FRP grid is controlled by the cross-sectional area,the number of layers and the grid spacing.The results show that the FRP mesh has obvious effect on the flexural strengthening.The specimens with low unit reinforcement have smaller bearing capacity,and the failure is mid-span grid fracture.On the contrary,the specimens with high unit reinforcement have higher bearing capacity,and the failure is the peeling of the interface layer between concrete and composite layer.3)The finite element software ABAQUS was used to model and analyze 5 beams in the flexural performance test.Using a cohesive model of bond slip at the interface between the composite layer and the concrete.The load-deflection curve,the mid-span strain curve and the component stress cloud diagram were extracted and compared.and the evolution process of interface damage was shown.The research results show that the established finite element model can effectively fit the cracking condition of concrete,and the fitting degree on the stressstrain condition of each component in the bending process is also high.The interface failure is occcurred in the shear span,along the vertical grid direction to the position of the support,and eventually the damage in shear span and support develop at the same time leading to interface failure;Summarizing the shortcomings of the existing calculation model about the bending capacity in FRP flexural reinforced concrete beams.Based on the adhesion performance test,flexural performance test and finite element simulation,an improved calculation model for the bending capacity about reinforced concrete beams strengthened with FRP grid is proposed,and compared with other scholars’ related tests.The research results show that the existing calculation model has a poor fitting degree to the specimens with peeling failure.The improved calculation model can effectively pre-test the stripping failure or breaking failure of the test piece.Comparison and verification with related experiments show that the improved calculation model established has higher accuracy and applicability,and can effectively predict the bearing capacity of FRP grid flexural reinforced concrete beams.