Research Of Structural Reinforcement And Repair With Magnesium Phosphate Cement Application

Magnesia-phosphate cement(MPC)is a kind of inorganic cementitious material which is completely different from traditional Portland cement.MPC is of excellent performance,such as high strength,rapid hardening,strong cohesiveness,and good mechanical stability.MPC can harden at low temperature and develop strength under negative temperature.MPC has good density and acid&alkali corrosion resistance.Based on these advantages,this kind of material has been applied to the rapid repair of highway,bridge and airstrip.However,the research of MPC focuses on material preparation and performance,and there are few research on its application to repair and reinforcement of structure.In order to solve the insufficient capacity of high temperature resistance and aging resistance of organic adhesive in repairing and reinforcing concrete structure,on the basis of the existing results of this research group,the inorganic cementitious material MPC was used to replace the organic adhesive in this paper,as a binder,the composition optimization design,physical and mechanical properties optimization and durability of MPC were studied,and the application effect of MPC in repairing and reinforcing structure was researched systematically.The main results are as follows:1.Composition design and performance optimization of MPC(1)Based on the study of the basic mechanical properties of MPC,such as tensile,compressive,flexural and tensile properties,MPC was shown to have high early strength.The addition of fly ash had a decreasing effect on flexural,tensile and splitting strength.Salt solution immersion and dry wet cycle conditions will affect strength and mass loss rate of MPC.The mass loss rate of quartz sand sample was the largest,while the loss rate of fly ash was the smallest.The main reason was that the incorporation of fly ash made the proportion of less harmful holes and harmless pores increased,the number of internal micro-cracks were relatively small.However,the incorporation of quartz sand made the number of less harmful holes and harmless pores decreased.There were many holes in the specimen,and the structure was loose.(2)The traditional toughness evaluation method ASTM-C1018 was improved,and the load-strain curve was used to assume the cracking point,which solved the problem that the traditional method was difficult to determine the cracking point by the load-displacement curve.The method of comprehensive evaluation of bending performance was established,and it was applied to the evaluation of the bending performance of MPC.It was found that the flexural properties of the samples without fly ash and sand were better.(3)In order to improve the comprehensive performance of MPC,the possibility of modification of MPC was studied by using hot material Graphene oxide(GO).The results showed that GO modification reduced the compressive strength of MPC.With the increase of GO content,the flexural strength,axial tensile strength and fracture toughness of MPC increased first and then decreased.When the content of GO was 0.035%,the flexural toughness and fracture toughness of MPC were increased by 24% and 12% respectively.Microstructure analysis showed that with the increase of GO content,the total porosity of MPC firstly decreased and then increased.The addition of appropriate amount of GO would fill the tiny pores of MPC,when the GO content was too much,not only improving the viscosity of MPC,but also the introduction of more bubbles,thereby reducing the strength and toughness of MPC.2.Study on the bonding ability of CFRP and concrete with MPC(1)The tensile bond strength test of CFRP and MPC with different ratio of MPC was carried out.The results showed that MPC with no fly ash had the same bond strength with organic adhesive.(2)A variety of test methods were used to study the capability of MPC bonded cement concrete,then the cement mortar and concrete specimens were bonded with MPC and the mechanical properties of them was tested.The results showed that MPC bonding specimen had better repair effect under the condition of splitting tensile and bending resistance,and could reach the performance of the original specimen.Under the condition of axial tension and shearing,the repairing effect couldn’t reach the level of the original specimen.The bending tests of MPC specimens were carried out through top thin layer thickening repair and docking repair.The results showed that MPC had good adhesion and 2 fracture models were proposed.Microscopic analysis showed that MPC could penetrate into the concrete matrix.The adhesion between hydration product Mg KPO4·6H2O and matrix made MPC have good bonding performance,in addition,the new hydration product at the interface made the bonding strengthen.3.Study on MPC bonded CFRP confined concrete column(1)The concrete cubes and columns were reinforced with CFRP bonded MPC and EP(organic adhesive),and the compressive strength and axial compressive performance were compared.The influence of number of CFRP layers and bonding reinforcement method on the performance of confining concrete specimens was presented.The strength model and finite element simulation method of MPC bonded CFRP confined concrete column were established.The results showed that MPC and EP had the same bonding effect,and the effective binding coefficient was increased by using MPC bonded CFRP compared with EP.(2)The innovative integrated technology of rust resistance and reinforcement was proposed.Using CFRP as reinforcing material and anode,using MPC as binder to replace organic adhesive without conductivity and permeability,the integrated technology of rust resistance and reinforcement was proposed firstly,which had dual function with electrochemical extraction of Cl-and FRP reinforcement.This technology made the extraction rate of Cl-ion exceed 70%,at the same time,made the ultimate compressive strength and displacement of concrete columns more than doubled.4.Study on MPC bonded CFRP strengthened concrete beam and reinforced concrete beam(1)The short concrete beams were reinforced with CFRP bonded MPC and EP,and the interface failure modes,flexural strength and load-strain law were compared and studied.The flexural performance of short reinforced concrete beams were evaluated by bending evaluation method in this paper.The influence of number of CFRP layers,concrete strength grade,adhesive type on the variation rule of bending load-strain curve was proposed.A better method of reinforcement was put forward,which provided the basis for the design of structural members.(2)The reinforced concrete beams were strengthened with CFRP bonded MPC and EP,and the failure mode,bearing capacity,load-deflection curves,the strain of CFRP and reinforcement were studied and compared.The results showed that the performance of MPC bonded CFRP was superior on reinforcing concrete beams.The simulation analysis method of strengthing reinforced concrete beam was established.The finite element analysis results were in good agreement with the experimental results and could predict the limit state and damage process.The reinforcement calculation was carried out by bending theory,and the results showed that the theory and design method of Degin Code for Strengthening Concrete Structure(GB50367-2006)were applicable to the design of the normal section bearing capacity of reinforced concrete beams strengthened with MPC bonded CFRP.