Experimental Study On Concrete Beams Reinforced With Magnesium Phosphate Cement Modified And Bonded With Carbon Fiber Cloth

Strengthening concrete structure with CFRP is a common method for structural reinforcement,which is widely used in the reinforcement and reconstruction of engineering structures.Researchers at home and abroad have carried out many studies on strengthening concrete structure with CFRP,and the research results confirm that the reinforcement method has obvious reinforcement effect and broad application prospect.However,most of the structural adhesives used at present are epoxy resin adhesives with easy aging and poor resistance to high temperature,and there are few studies on the use of inorganic cementitious materials to paste CFRP.In order to prepare inorganic cementitious materials suitable for pasting CFRP,magnesium phosphate cement was modified in this thesis.Firstly,the influence of the content of self-made composite modifier（SCM）（0%～5%）on the properties of magnesium phosphate cement was studied,including working properties,mechanical properties and hydration heat release rate.Combined with XRD and SEM,the mechanism explanation of the change law was put forward,Then,the effects of Mg O/KH₂PO₄molar ratio（5～8）,water-binder ratio（0.20～0.26）and retarder（PCM）content（0.9%～1.8%）on its fluidity,setting time and mechanical strength were studied,and the influence law was revealed by SEM;After that,three reinforced concrete beams B0,B1 and B2 were designed and poured.B0 was not reinforced.B1 used magnesium phosphate cement to paste CFRP for flexural reinforcement,B2 used epoxy resin adhesive to paste CFRP for flexural reinforcement,and adopted three-point loading.The reinforcement effect of magnesium phosphate cement bonded CFRP was studied by comparing the failure process,bearing capacity,mid span deformation and mid span concrete strain of the test beam.The main conclusions of this thesis are as follows:（1）The higher the content of SCM,the longer the setting time of MPC slurry,and the longest setting time is 76.5min;After adding an appropriate amount of SCM,MPC no longer has strength shrinkage;When the content of SCM is less than 2%,the compressive strength of MPC increases with the increase of SCM content.When the content exceeds 2%,the compressive strength gradually decreases,and the maximum compressive strength is 82.1MPa;The reason why SCM inhibits MPC frost may be that SCM improves the stability of KH₂PO₄solution.（2）The hardening time and fluidity of MPC paste decrease with the increase of M/P,while the compressive strength decreases;With the increase of water-binder ratio,the hardening time and fluidity of MPC slurry increase,and its flexural and compressive strength decrease;Similar to the water-binder ratio,the hardening time and fluidity of MPC slurry increase and its strength decreases with the increase of PCM content.（3）Compared with the unreinforced beam,the test beam strengthened with MPC has more cracks,develops more slowly,and the bearing capacity is increased by 23.1%.After reinforcement,the flexural stiffness is improved,the mid span deflection is smaller,and the reinforcement effect with MPC is obvious,but it is slightly worse than that with epoxy resin adhesive at normal temperature.