Development Of Magnesium Phosphate Cement Mortar For Rapid Repair Of Wall Cracks

Magnesium phosphate cement(MPC)is a new type of cementitious material,which has the advantages of fast hardening early strength,high bonding strength,dry shrinkage,and setting hardening at low temperature.It is widely used in rapid repair of highway bridges.The repair of cracks in buildings is affected by complex construction conditions.The performance requirements of the repair materials in terms of setting,hardening and durability are high,and the existing materials cannot meet the repair requirements.The further application of magnesium phosphate cement to repairing cracks in the house is of great significance for expanding the application of MPC cement and developing house repair technology.The paper focuses on the following four aspects of research work on the development of rapid repair of MPC applied to wall cracks:(1)According to the relevant provisions in the design specification of concrete structure reinforcement,the flexural strength,bonding strength and water resistance of magnesium phosphate cement mortar are modified.The test results show that: optimizing the ratio of phosphate component to magnesium oxide can improve the flexural strength and bonding strength of magnesium phosphate cement mortar;after incorporating micro silica fume,using magnesium phosphate cement hydration heat can induce the excitation of dioxide Silicon participates in the reaction,significantly improving the water resistance of MPC cement mortar.The prepared MPC cement mortar has good mechanical properties,controllable set hardening time,higher bonding strength and excellent water resistance,which can meet the performance requirements of rapid wall repair.(2)Using X-ray diffraction and scanning electron microscopy and other experimental methods,the mechanism of the setting and hardening of magnesium phosphate cement was analyzed and discussed.Through X-ray diffraction analysis,it was found that the main hydration product of MPC cement without microsilica fume was struvite,and after mixing with microsilica fume,a new cementing material(magnesium silicate)was generated.SEM results show that when M / P is 3,the formation and arrangement of crystals are relatively dense.After adding fly ash,the spherical crystals of fly ash,struvite and magnesium oxide crystals combine to form a relatively dense whole.The twist-like crystals generated after the addition of micro-silica fume connect the crystals to each other to improve the mechanical properties of MPC mortar.(3)The performance of MPC mortar is discussed.The research results show that MPC mortar is neutral,with good volume stability and strong corrosion resistance,and can be applied to repair cracks in walls.Use MPC cement mortar to repair the broken concrete test block and red brick test block to evaluate the repair effect of MPC cement mortar on the wall material.The mechanical properties of the repaired concrete and red brick test blocks are improved to a certain extent compared with the samples before fracture,indicating that MPC mortar has excellent bonding strength to the red brick and concrete materials.The test results of MPC mortar with water for repairing leaked concrete samples show that MPC mortar can be used to quickly repair wall leakage,which solves the long-term technical problems of water repair for leaks.(4)Using ABAQUS simulation software,the wall model was established,and the stress and displacement states of the crack-free wall,crack-unrepaired wall and crack-repaired wall under temperature load were compared and analyzed.The finite element calculation results show that MPC cement mortar can effectively reduce the stress concentration at the cracks of the wall,and has a good work synergy with the concrete wall.