Study On Modification Method And Properties Of Magnesium Phosphate Cement-based Repair Material

With China’s economic development,the market demand for repair and maintenance of existing construction facilities is increasing.As a new type of green low-carbon cement,magnesium phosphate cement has the characteristics of high early strength and rapid setting.It is well used in low-temperature construction and road emergency repair projects.In this paper,the modification method and bonding properties of potassium magnesium phosphate cement-based materials were studied.Firstly,the effect of raw materials on the properties of MPC was studied.Pre-reacted MgO was prepared by the reaction of MgO with pretreatment agent.The effects of pre-reacted MgO and the fineness of KH₂PO₄ on the properties of MPC were studied.The results indicated that both pre-reacted MgO can prolong the setting time of MPC,and the compressive strength of MPC with 6%H₃BO₃ pre-reacted MgO was the highest.The mechanical properties of MPC made of powder KH₂PO₄ were better than those of granular KH₂PO₄.The compressive strength of MPC prepared by 6%H₃BO₃.pre-reacted MgO and powdered KH₂PO₄ was 64.8Mpa in 28 days,about 60%higher than that of the blank group.Secondly,the bonding properties between MPC and different substrate materials were studied by adjusting the water binder ratio and magnesium phosphorus ratio of MPC.It was found that the bonding between MPC paste and red brick and ordinary portland cement mortar mainly depends on the chemical bonding between interfaces.The bonding between MPC paste with 0.20 water binder ratio and 2:1 magnesium phosphorus ratio and the two materials was the best.The 14d tensile bonding strength was 1.82MPa and 2.38MPa respectively.The holding force of MPC mortar on rebar decreased with the decrease of MPC water binder ratio and magnesium phosphorus ratio,sine the holding force of MPC mortar on rebar depended not only on the chemical combination between materials,but also on the shrinkage stress caused by the volume shrinkage of MPC mortar.Finally,by adjusting the composition of MPC,the effects of cellulose ether,waterborne epoxy resin and silica fume on the setting time,fluidity,adhesion,compressive strength and wear resistance of MPC were studied.The results indicated that the addition of cellulose ether and waterborne epoxy resin can significantly improve the bonding performance,compressive strength and wear resistance of MPC.The 28d compressive strength of 0.7%cellulose ether and waterborne epoxy resin MPC was 73.3MPa and 71.9MPa respectively.The reason was that the incorporation of cellulose ether can form a network structure in MPC,which increases the overall mechanical properties of the material.The addition of waterborne epoxy resin can promote the growth of hydration products make Mg KPO₄·6H₂O particles larger.The addition of silica fume basically does not participate in MPC hydration reaction.The addition of silica fume within 6%could improve the setting time and flow performance of MPC to a certain extent without affecting the 28d compressive strength.However,when the content of silica fume exceeded 6%,it was easy to aggregate in the slurry,which significantly reduced the bonding performance,compressive strength and wear resistance of the material.