Bonding Properties And Mechanism Study Of Fiber Reinforced Magnesium-potassium Phosphate Cement Mortar

With the development of the structure reinforcement industry,higher requirements have been proposed for the performance of reinforcing materials.Magnesium-potassium Phosphate Cement(MKPC)is a new kind of environmentally friendly cementitious material,which also has the characteristics of chemically bonded ceramics.It has become one of the research hotpots in structure reinforcement area in recent years due to its advantages of quick setting,early strength,good volume stability and high bonding strength.The key to success or failure of reinforcement project is the bonding properties of reinforcing materials.By taking the bonding properties of fiber reinforced magnesium-potassium phosphate cement mortar(FMPM)as the research object,firstly,the basic mix proportion of FMPM was determined based on a series of basic performance tests.Secondly,the improvement effects of single or duplicate mixes of fly ash and silica fume on the optimized performances(fluidity,compressive strength,flexural strength,bond strength,water resistance,elastic modulus)of FMPM were studied,and a mix proportion of FMPM with optimum overall performance was obtained.Thirdly,the bonding performance between FMPM and the strengthened concrete was studied.Finally,by the pore structure analysis test,XRD and SEM microstructure test,a mechanism analysis has been conducted to explain the macroscopic properties of FMPM.The main conclusions are drawn as follows:1.With the decrease of P/M(the quality ratio of KH2PO4 to MgO)from 1/2 to 1/5,the fluidity,bond strength,compressive strength and flexural strength of FMPM increase at first and then drop.When P/M is 1/3,the amount of cement hydration products(MgKPO4 · 6H2O)reaches the peak,therefore the bond properties of FMPM are the best.2.With the increase of silica fume content from 0%to 20%,the improvement of the combination property of FMPM increases at first and then drops when silica fume(SF)is added alone into paste.When the mass ratio of SF is 10%,the combination property of FMPM is the best,with the bond strength of FMPM 36%higher than that without SF.The SF creates hydration reaction with magnesium-potassium phosphate cement,and the hydration product MgSiO3 makes hydration structure compact.The SF also has physical filling effect in FMPM.Moreover,the particles of SF cover densely on the surface of MgO,which can delay the setting time of FMPM to pour the mortar more close-grained.So the SF increases the bond strength between FMPM and old concrete significantly.3.With the increase of fly ash content from 0%to 20%,the combination property of FMPM decreases when fly ash(FA)is added alone into paste.The FA has physical filling effect in FMPM.Because the carbon granules in the FA has a absorption to monopotassium phosphate,the SF has a signficant impact on the performance of FMPM in early days,but the impact decreases as time goes on,and the strength of FMPM is lower than that without FA at last.When the mass ratio of FA is 5%,the bond strength is only 1%lower than that without FA,but the bond strength of FMPM decreases obviously with the increase of the amount of admixture of FA.4.When double mixed with SF and FA,the impact on the bond properties of FMPM falls in between that with SF added alone and that with FA added alone.However,the pore structure of FMPM becomes compact because the distribution of grain size is reasonable.The contribution of SF to the microstructure is increasing the ratio of harmless hole,and the contribution of FA to the microstructure is increasing the ratio of less harmful hole on the basis of the fact that both of SF and FA can reduce the harmful hole of FMPM.5.The bond strength between FMPM and strengthened concrete is better than that of ordinary Portland cement.FMPM is excellent when it works together with old concrete,and it has significant strengthening effects.