Study On Acid Resistance Of Modified Magnesium Phosphate Cement

Magnesium Phosphate Cement(MPC)is a new type of cementitious material with advantages of high early strength,strong adhesion,good abrasion resistance and small shrinkage.It is widely used in roads,bridges,airport runways,as well as military repairs and harsh environmental repairs.As a rapid repair material,magnesium phosphate cement has a wide variety of application environments,such as the repair of plant and sewage plant walls and pipelines in an acidic environment,and the acidic environment imposes requirements on the application of magnesium phosphate water.Therefore,the study of magnesium phosphate cement has been conducted.Acid resistance is of great significance.This article first studied the effect of raw materials and mix ratio on the setting and hardening properties of magnesium phosphate cement,and then improved the resistance of magnesium phosphate cement to sulfuric acid,hydrochloric acid,and nitric acid by adding fly ash and changing the mix ratio,using a combination of macroscopic and microscopic methods.The coagulation time,mechanical properties,hydration heat release law,hydration products and micro-morphology of magnesium phosphate cement mortar were tested.The acid corrosion resistance of modified magnesium phosphate cement was studied.The main conclusions are as follows:The effects of MgO sintering temperature,phosphate type,borax and fly ash content on the setting and hardening properties of magnesium phosphate cement were studied.The hydration and exothermic properties of MPC cement under different acid environments were also studied.The results show that the use of MgO with a reburning temperature of 1800 ℃ to produce magnesium phosphate cement can effectively prolong the setting time.The setting time of magnesium phosphate cement prolonged with the increase of borax content,but the mechanical strength of magnesium phosphate cement decreased with the increase of borax content.The use of K2HPO4 magnesium phosphate cement can effectively extend the setting time,but the mechanical strength will decline.When the content of fly ash is more than 40%,the setting time of magnesium phosphate cement will be prolonged.The addition of fly ash can effectively reduce the hydration heat release rate of MPC while reducing the total amount of hydration heat release,Water environment,HCl solution environment can increase the total hydration of MPC heat.The effects of fly ash and magnesium/phosphate ratio on the mechanical properties and corrosion resistance of magnesium phosphate cement were studied under natural conservation and acid solution conservation of magnesium phosphate cement.The results showed that magnesium phosphate cement with 4:1 magnesium and phosphorus ratio had the highest flexural strength under natural conservation.The compressive strength of magnesium phosphate cement with 6:1 magnesium and phosphorus ratio was the highest.Under the condition of acid solution curing,the corrosion resistance coefficient of 6:1 magnesium phosphate cement is the largest.Under natural conservation,the compressive and flexural strength of magnesium phosphate cement with 45%fly ash content is the highest,while the content of fly ash has the same influence on the corrosion resistance of magnesium phosphate cement under acid solution maintenance condition.At the acid solution curing conditions,the corrosion resistance coefficient of magnesium phosphate cement with 15%fly ash content is the largest.Under the conservation of acid solution,the compressive and flexural strength and the corrosion resistance coefficient of magnesium phosphate cement mortar with pH = 1 were the lowest when the ratio of magnesium to phosphorus was 5:1 and the content of fly ash was 35%.The effects of different concentrations and types of acid solution environment on hydration products and microscopic morphology of magnesium phosphate cement were studied.The result of XRD results showed that no new hydration products were formed in the MPC cured in the acid solution,and the production of the main hydration product KMgPO4 6H2O decreased as the concentration of the acid solution increased,compared to the HNO3 solution and the H2SO4 solution.The production of MPC hydration product KMgPO4 6H20 in the pH 1 HCl solution is the least.The addition of fly ash will increase the production of MPC hydration product KMgPO4 6H2O.The SEM results showed that the acid solution could dissolve or precipitate KMgPO4 · 6H2O,a hydration product of MPC,resulting in more pores in MPC.The MPC with fly ash incorporates a more intensive micro-morphology and the fly ash effectively fills the pores,indicating that fly ash can improve the acid corrosion resistance of MPC.