Research And Application Of Double Liquids Injection Method To Prepare Magnesium Phosphate Cement And Its Repair Materials

Magnesium Phosphate Cement（Magnesium Phosphate Cement,MPC）is an inorganic gelled material consisting of dead burned magnesia and ammonium dihydrogen phosphate.It is prepared in accordance with a certain proportion.After mixing with water,an acid-base neutralization reaction will occur to form a chemical bond,and the bond will synthesize magnesium ammonium phosphate（Mg NH₄PO₄·6H₂O）,which is the main source of strength.It has a broad prospect in repairing expressway,airport runway and military industry.However,the fluidity and permeability of cement-type grouting materials are poor,and some materials have very strict requirements on curing time,temperature and humidity,which makes it difficult to inject the tiny pores of the structure layer,and it is easy to cause secondary pulping,which will cause the second falling off.In the case of road repair,the laying time is short and the environment will not affect the repair materials.Therefore,it is important to search for a kind of adhesive strength,fluidity and permeability that can not only solidify quickly but also have high bond strength.This thesis studied the preparation of magnesium phosphate cement by double liquids injection method,and explored the influence of the addition of different admixtures and the properties of magnesium oxide on the properties,micro-morphology and pore diameter distribution of magnesium phosphate cement.In addition,through the modification of MPC and formulate magnesium phosphate cement mortar mix proportion design,compared with the national standard,test its meet the performance requirement.The main research results are as follows:（1）In the MPC prepared by double-liquid grouting method,the effect of adding naphthalene water-reducing agent（PNS）to liquid A is not obvious,while the addition of PNS with different contents to liquid B has a certain effect on the fluidity of the slurry,which has a good water reducing effect.By using orthogonal experiment found that adding 0.3%in liquid A of PNS,add 0.8%of PNS in liquid B,the best effect,the final setting time reached 34 min,28d strength of 32.5 MPa.With the continuous increase of PCE,the strength and water resistance of the matrix show a trend of first increasing and then decreasing.The maximum fluidity can reach 245mm,and the maximum strength of 1h under natural curing can reach 31.7MPa,and the maximum strength of 28d is 108.5 MPa.The strength retention rate decreased by about 40%from 7 to 210 days after immersion.（2）Different calcination methods and different magnesium oxide content have certain influence on MPC performance.The fluidity of MPC increases with the increase of magnesium oxide content,and the setting time increases with the increase of average grain size of magnesium oxide.And the average grain size of magnesium oxide preparation of MPC has reached the highest intensity,the greater the average grain size of magnesium hydroxide was prepared by the MPC and mechanical properties of the best,step calcination method is used to produce,magnesium oxide content in about 92%of the dead burned magnesia the average grain size of the largest,reached 129.45 nm,the fluidity of the MPC for preparation of 220 mm,final setting time at 38 min,7 d strength in 65.0 MPa,reached the highest.And the addition of silica fume the grain size of different magnesium oxide the compressive strength of MPC is prepared first increased and then decreased,and silica fume on the MPC kinds of hydration products and no more,improves the porosity of the MPC,increased the density.According to the national standards,MPC mortar mix ratio was determined by combining literature retrieval and experiment.The flexural strength of the MPC mortar for 3 h and 3 d is 3.3 MPa and 6.7 MPa respectively.Moreover,the flexural strength of the simulated MPC repair sample at 3 h interface is 5.3 MPa,that is,it conforms to the standard JC/T 2537-2019,which meets the standard and provides technical support for the application of magnesium phosphate cement repair mortar in engineering.