Study On Magnesium Phosphate Cement Of Concrete Vertical Fa(?)ade Repair Agent And Engineering Application

The protection layers of concrete structures such as facade,wall,roof,and the pier and the bottom of the bridge,are generally damaged,of which the repairing is a huge challenge.On the one hand,the repairing place is vertical facade or the bottom surface,not the flat surface.Due to the special nature of such repair position,it make the repairing material flow to the lower location under its own gravity,which requires repairing material is fast setting and hardening,no liquidity and high bond strength etc.;On the other hand,the broken body of the housing wall and the bottom surface of bridge caused great threat to life and property of residents and pedestrians,especially in the street of the buildings and in the roads of the city bridge and other places.Without considering pedestrians,vehicle safety and traffic jams,silicate cement mortar is usually used to repair,so at least one month cycle is needed,and winter construction period is longer.Magnesium phosphate cement based material is a new type of air hardening cement material.It has many characteristics,such as rapid hydration,hardening,high early strength,high bonding strength,high volume stability,wear resistance,fire resistance and frost resistance,which is over traditional Portland cement.Therefore,this paper innovatively develops magnesium phosphate cement based concrete vertical facade repair agent,which is specially designed for the facade and bottom surface of buildings and structures.After actual engineering inspection,the repair effect is good.Through the cement mortar dry shrinkage test,we study the different Magnesium Oxide activity,fineness,water cement ratio,magnesium phosphorus ratio and fly ash content on magnesium phosphate cement concrete facade repair agent(hereinafter referred to as the MPC facade repair agent)shrinking effect.The results show that the higher MgO activity,without milling,magnesium phosphorus ratio of 4:1,30%fly ash,0.18 water binder ratio of MPC repairing agent,of which the shrinkage control is better.By changing the repairing concrete strength grade,the water content of bonding interface,interface treatment and maintaining conditions,we study on the adhesion of MPC vertical facade repair agent and the matrix concrete.The results show that the higher level of matrix strength,tensile bond strength of the interface is higher.In the natural maintaining conditions,tensile bond strength of the interface is at least 2.4MPa,which meet the construction repair requirements;MPC repair agent has a good adhesion physically and chemically because of the van Edward force and mechanical bite force,and cooperation effect.Through the cement mortar dry shrinkage test,freeze-thaw cycle test,plate cracking test,we study different ratio of polypropylene fiber on dry shrinkage resistance,frost resistance and crack resistance of the MPC repair agent.The results show that the proper addition of polypropylene fibers can improve the shrinkage resistance the MPC repair agent.1.1kg/m3 polypropylene fibers can improve relative dynamic elastic modulus and mass loss index of MPC facade repair fiber agent.As the fiber content increases,the Acr of MPC facade repair agent gradually decreased,and ? is higher.Finally,in order to testify the application effect of laboratory research,we apply MPC repair agent to Shenyang Construction University and the Shenyang Baishan bridge.After 24 months and 12 months,the bottom of the bridge has not damaged any more,and the wall facade of the dormitory has not been damaged any more.In summary,MPC repair agent has good durability,which is a kind of quick repairing material for broad application prospects.