Effect Of Modified Magnesium Oxysulfide Cement On Thermal Performance Factor Study

Ordinary magnesium sulfate cement is a kind of magnesite cement.It is a three-component cementation system of MgO-MgSO4-H2O composed of active MgO powder and a certain concentration of MgSO4 solution.It has been known and studied for a long time in our country.Compared with ordinary cement,ordinary magnesium sulfate cement has many good properties,such as insensitive to high temperature,good water resistance,light weight,etc.,but at the same time,it also has some disadvantages,such as low strength,incomplete hydration,etc.,which limits the use of ordinary magnesium sulfate cement in some fields.The main purpose of this experiment is to explore the heat change,quality change,phase change,micro morphology change and later strength change rule in the process of heating under the premise of improving the strength of ordinary magnesium sulfate cement,in order to develop the possibility of its service in high temperature enviro nment and high temperature resistance.In the experiment,a new type of modified magnesium oxysulfide cement was developed on the basis of ordinary magnesium sulfate cement by adding modifier to improve the strength.The effect of the type and amount of modifier on the strength of ordinary magnesium sulfate cement at different ages was studied.Secondly,in order to explore the influencing factors of the mechanical and thermal properties of the modified magnesium oxysulfide cement,the dynamic calculation of the thermal decomposition reaction of the modified magnesium oxysulfide cement was carried out according to the thermodynamic data,and the graded activation energy of the reaction was obtained,which proved the heat-resistant and fire-resistant performance of the modified magnesium oxysulfide cement material,and clarified the decomposition reaction process after heating.At the same time,it was found that the modified magnesium oxysulfide cement material The strength of the magnesium oxychloride cement decreased rapidly after heating.The 517 phases were decomposed into anhydrous basic MgSO4 before 400℃,and decomposed to MgSO4 and MgO at 800℃.The decomposition of MgSO4 at 1000℃ or above resulted in the formation of MgO with higher activity and reacted with water to form Mg(OH)2 gel phase,which made the material lose strength and could not guarantee normal use under long-term conditions.In order to improve the heat-resistant limit and high-temperature strength of modified magnesium oxysulfide cement,the composite modifier and admixture were studied.Five kinds of calcination temperature and different holding time were determined.The modified magnesium oxysulfide cement was heated to 200℃,400℃,600℃,800℃,1000℃ at 10℃/min respectively,and kept for 2 h,4 h,6 h,8 h,12 h and 24 h.The results were analyzed by SEM(By means of SEM,XRD and TG-DSC,the microstructure,mineral composition and the amount of 5Mg(OH)2·MgSO4·7H2O(517 phase)in MgSO4 cement under different calcination systems were analyzed.The experimental results showed that the addition of composite modifier was beneficial to the formation of 517 phase in MgSO4 cement Semi quantitative analysis shows that 517 phase is the most and the peak strength is high,which indicates that 517 crystal is well developed.By introducing composite additives,fly ash or silica fume into Magnesium oxysulfide cement,the strength of Magnesium oxysulfide cement after heating can be improved to a certain extent,which provides a theoretical basis for the application of Magnesium oxysulfide cement in the field of high temperature.Among them,the sample with 1.3%composite admixture has the highest strength after firing at 500℃,reaching 45.3 Mpa,which is 55.8%higher than that of the clean slurry.The sample with 20%silica fume shows the phenomenon of shrinkage and expansion after heating.The strength after firing at 500℃ reaches 38.5 Mpa,which is 35%higher than that of the clean slurry.