Experimental Study On Axial Compression Performance Of Reinforced Concrete Columns Strengthened With Magnesium Phosphate Cement And Carbon Fiber Clot

With the expansion of existing construction scale,the excessive energy consumption and excessive carbon dioxide emission in the construction industry will become a problem that must be solved in the national development.Therefore,the focus of construction from new building to the maintenance and transformation of the existing building will be called the important trend of the development of the construction industry in the future.In the past30 years,external fiber reinforced polymer(FRP)reinforcement method has been widely applied to reinforce concrete structures.However,the high temperature resistance of epoxy resin adhesive used in FRP strengthening method brings hidden dangers to FRP strengthening technology and limits its application range.In view of this,it is of great significance to replace epoxy resin with inorganic adhesive in FRP strengthening technology to make up for its high temperature resistance defect.Magnesium phosphate cement(MPC)is a new type of green inorganic adhesive,which can replace epoxy resin and has great potential to improve the high temperature resistance of FRP reinforced concrete technology.At present,the application of magnesium phosphate cement in reinforcement of concrete structure is lacking.In this thesis,the axial compression properties of magnesium phosphate cement reinforced plain concrete cylinder and reinforced concrete cylinder with carbon fiber cloth are studied systematically by means of experimental research and theoretical analysis.The main research contents are as follows:Firstly,the axial compression tests of 21 carbon fiber cloth reinforced concrete cylinders were made,and the effects of two parameters,the type of adhesive and the number of carbon fiber cloth layers,on the axial compression properties of the columns were studied.The test results show that:(1)Compared with unrestrained concrete specimens,the strength of magnesium phosphate based C-FRi P reinforced specimens is increased by 1.69 to 2.50 times and the ultimate strain is increased by 1.83 to 3.50 times.Compared with the FRP reinforced specimens on epoxy resin,the strength and ultimate strain of the magnesium phosphate based C-FRi P reinforced specimens are about 95% and 60% of the FRP reinforced specimens,respectively,under the same fabric dosage.(2)The strain efficiency factor of magnesium phosphate based C-FRi P system is 0.33,which is much lower than that of FRP system like most FRCM systems.(3)The DIC test results showed that the Von Mises strain evolution of FRi P-constrained specimens was similar to that of FRP-constrained specimens,and the strain distribution was more uniform with the increase of constraint stiffness.It is proved that the stress distribution in thicker FRP sheath is more uniform,and the failure mode of FRi P bound specimens is more similar to that of FRP bound specimens.Then,the axial compressive properties of 7 carbon fiber sheets reinforced large reinforced concrete columns were tested,and the effects of strip spacing and adhesive types on the axial compressive properties of the columns were studied.The ultimate bearing capacity and ultimate strain of the FRP and FRi P columns were compared under the same constraints.The test results show that the bearing capacity of unconfined concrete columns is increased by 28.6%,43.9% and 47.1%,respectively.Compared with FRP columns,the bearing capacity is 102.7%,97.8% and 97.3% of the bearing capacity of FRP columns under the same conditions,respectively.The results show that the bearing capacity of FRi P and FRP columns is similar,and both of them have a good strengthening effect on unconstrained columns.The axial limit strain of FRi P confined columns is only 66.2%,68.4% and 77% of the axial limit strain of FRP confined columns under the same conditions,which indicates that the ductility improvement effect of MPC series specimens is lower than that of EP series specimens.Finally,six existing classical models of FRP and FRCM confined concrete are evaluated,and the semi-empirical models of ultimate strength and strain of confined concrete in magnesium phosphate based C-FRi P system are obtained by fitting the experimental data based on the theories or important parameters proposed in the existing models.According to the existing research theories of FRP strip-constrained concrete and FRP constrained reinforced concrete,a calculation model of the bearing capacity of reinforced concrete columns constrained by C-FRi P system based on magnesium phosphate is established based on experimental data.