Preparation Of Magnesium Phosphate Cement And Its High Temperature Performance Study

Magnesium phosphate cement is a magnesium cementitious material,compared to ordinary silicate cement,has the advantages of high early strength,fast hardening,corrosion resistance,dry shrinkage,strong bond with old concrete,etc.,can be applied to the rapid repair of roads and bridges,military engineering rescue strong construction,curing heavy metal ions and other fields.When magnesium phosphate cement is applied in these fields,all have high requirements for temperature stability,and need to maintain a better structure and performance in the event of fire or in the face of high temperature,and cannot be defective to the point of unusable under high temperature,so it is important to study the high temperature resistance of magnesium phosphate cement.In this thesis,magnesium phosphate cements were firstly prepared by changing the magnesium-phosphorus mass ratio and phosphate type,and the basic properties of magnesium phosphate cements were studied,and the effects of magnesiumphosphorus mass ratio on setting time,flow rate,and mechanical properties at different ages of ammonium magnesium phosphate cement and potassium magnesium phosphate cement were analyzed.The physical phase composition and content and microstructure of the specimens were characterized by XRD,SEM,TG-DSC and other testing equipment systems.Then the high temperature performance of magnesium phosphate cement was studied by changing the magnesium-phosphorus mass ratio and phosphate type to hold the cement from 200℃ to 1200℃,and the effect of magnesium-phosphorus mass ratio on the apparent morphology,mass loss,volume stability and strength loss of ammonium magnesium phosphate cement and potassium magnesium phosphate cement after high temperature was analyzed,and the ratio with the best performance after high temperature was selected.Finally,silica fume was used as external admixture to study the effect of silica fume on the performance of magnesium phosphate cement,and the effect of silica fume on the apparent morphology,mass loss,volume stability and strength loss of magnesium ammonium phosphate cement and magnesium potassium phosphate cement after high temperature was analyzed.The main research and findings of this thesis are as follows.(1)As the mass ratio of MgO to phosphate increases,the contact area between MgO and phosphate increases during the reaction,so the setting time and flow rate of ammonium magnesium phosphate cement and potassium magnesium phosphate cement are gradually reduced.(2)When the mass ratio of magnesium and phosphorus is low,due to the lack of water involved in the reaction affects the generation of guano stone in the strength phase,so the content of guano stone in the specimen increases with the increase of the mass ratio of magnesium and phosphorus shows a trend of increasing first and then decreasing.(3)When the holding temperature exceeded 1000℃,the magnesium ammonium phosphate specimens with Mg: P mass ratio of 5:1 and 6:1 could maintain the overall structural stability and reduce the mass loss,but the Mg: P mass ratio did not significantly affect the structural stability and mass loss of MKPC specimens.(4)With the increase of magnesium phosphorus mass ratio,the residual compressive strength of magnesium ammonium phosphate cement and potassium magnesium phosphate cement after holding at different temperatures was gradually enhanced.The highest residual strength of ammonium magnesium phosphate cement after high temperature is 6:1,and the highest residual strength of potassium magnesium phosphate cement after high temperature is 5:1.(5)The addition of silica fume reduced the room temperature compressive strength of magnesium phosphate cement and increased the residual strength after holding at different temperatures.Silica fume improved the compressive strength of magnesium phosphate cement between 200℃ and 600℃ through filling effect;from800℃,silica fume improved its high temperature performance by promoting the generation of magnesium olivine,and the generation of magnesium olivine increased with the increase of temperature,and the dense structure formed by volume shrinkage at high temperature and magnesium olivine together improved the compressive strength of magnesium phosphate cement.