Experimental Study On Interfacial Bond Behavior Of MPC-NSM-GFRP Reinforcement System With Curing Age And Admixture

The NSM-FRP reinforcement technology is a concrete structure reinforcement method flourished in recent years.In the NSM-FRP reinforcement system,epoxy resin is commonly used as a binder.Though it has high bond strength,yet it still has many problems,such as high price,poor high temperature resistance,easy degradation,low temperature curing and so on.Magnesium phosphate cement?MPC?is a new type of inorganic cementitious material,which has advantages of low price,good high temperature resistance,good durability and fast curing at low temperature.In view of this,this paper selected magnesium phosphate cement as a new type of binder,and researched the bonding behavior between GFRP rods and concrete interface under the action of epoxy resin binder using single shear pull-out test.The main research contents are as follows:Firstly,the optimum mix ratio of MPC was investigated through the basic mix ratio tests.The testing results indicate that the setting time of MPC extends with the increase of borax dosage,while the compressive strength decreases;the MPC's setting time is shorten with the increase of MgO/KH₂PO₄?M/P??molar ratio?,while the compressive strength increases;the MPC's setting time is shorten with the increase of fly ash content in a certain increment,while the compressive strength increases.Finally the best mix ratio was obtained through large experiment results coMParing analysis.On this basis,the effects of curing age on the bonding interface properties of NSM-GFRP system for the binder of MPC and epoxy resin were studied by experiment.The testing results indicate that despite the bond strength of MPC is lower than that of epoxy resin under the same age condition,the damage of the MPC test pieces all occurs in the concrete layer,which can be strengthened,and the bond strength increases with the extension of age.Finally,the effect of two kinds of admixtures of silica fume and calcium carbonate whisker on NSM-GFRP system bonding behavior modification under MPC binder was studied in order to solve the problem of the decrease of bond strength caused by the prolonged retardation time of MPC binder.The testing results indicate that the bond strength of the MPC test pieces increase and the bonding properties of magnesium cement improve by mixing with a certain amount of silica fume??6%?or a certain amount of calcium carbonate whiskers??0.6%?in the MPC matrix.But there is no obvious effect on the adhesion of MPC binder by mixing with silica fume and calcium carbonate whiskers?doped with 6%silica fume+0.6whiskers?.The bonding properties of the MPC binder decrease when mixing with high proportion of calcium carbonate crystal?incorporating 6%silica fume+0.9 whiskers?.