Study On Sulfate Resistance Of Modified Potassium Magnesium Phosphate Cement Mortar

Magnesium Phosphate cement（MPC）is a new type of cementing material with fast hardening and early strength,which plays an important role in the field of repair materials.However,since the raw material of magnesium phosphate cement is NH₄H₂PO₄,it often releases unpleasant gases,which will not only affect the equipment,but also be unfavorable to environmental protection.Therefore,many scholars have found that KH₂PO₄ can replace NH₄H₂PO₄ to prepare potassium magnesium phosphate cement（MKPC）to overcome the defects.The hydration mechanism and hydration products of potassium magnesium phosphate cement are similar to those of magnesium phosphate cement.The hydration product is the same kind of MgNH₄PO₄·6H₂O.Therefore,it has the same material properties as magnesium phosphate cement,and even more advantages.With the increasing demand for potassium magnesium phosphate cement,the research of potassium magnesium phosphate cement has become more and more simple.This paper mainly studies the modification of potassium magnesium phosphate cement mortar and the durability of the modified mortar.By adding nickel slag,steel slag and fly ash into potassium magnesium phosphate cement,the influence of the mineral admixture on strength,hydration heat and deformation of cement mortar is studied.It provides the basis for the modification of potassium magnesium phosphate cement mortar.The mechanism of salt erosion of modified potassium magnesium phosphate cement mortar under dry and wet cycle,freeze-thaw cycle and electric pulse was studied.The effect of mineral admixture on salt resistance of potassium magnesium phosphate cement mortar was also investigated.The results show that the shrinkage deformation and flexural compressive strength of MKPC slurry are improved obviously when the content of nickel slag powder is 10%,and the optimum content of steel slag and fly ash is 5%.The degree of early hydration of MgKPO₄·6H₂O,the main hydration product,was obviously increased after the addition of appropriate amount of admixture,and the crystal morphology and size of the main hydration product,MgKPO₄ 6H₂O,were obviously increased,which made the structure of MKPC hardened body more compact.Potassium magnesium phosphate cement mortar containing 5%nickel slag shows good salt resistance under dry and wet cycle,freeze-thaw cycle and electric pulse.It is concluded that the physical and mechanical properties and salt corrosion resistance of potassium magnesium phosphate cement mortar can be effectively improved when the content of nickel slag is between 5%¹0%.In addition,the balance system of soaking and drying of MKPC mortar specimens was designed,and the mass loss and deformation of potassium magnesium phosphate cement mortar under dry and wet cycling conditions were studied.It is proved that the mass loss is mainly caused by the hydrolysis loss of MKP formed in the hardened MKPC mortar and the exfoliation of the specimen surface.