Modification And Application Of Magnesium Oxysulfate Cement

Magnesium oxysulfate cementitious Material has the advantages of light weight,fast setting time,high early strength,good volume stability,fire resistance,thermal insulation,heat insulation,anti-carbonation and no rust on steel.Compared with magnesium oxychloride cement,there are few researches on magnesium oxysulfate cement,due to the disadvantages of low strength and poor water resistance of traditional magnesium oxysulfate cement,which restrict its research and application in civil engineering.In this study,using the additive technology to the traditional magnesium oxysulfate cement on modification,with high strength,good water resistance and good carbonization resistance of the composite modified magnesium oxysulfate cement.The cement was investigated of the mechanical properties,water resistance,phase composition and the application in the civil engineering technology.First,under the conditions of magnesium oxysulfate cementitious material at room temperature,the ratio of the basic test,the compressive strength of the test to find out the solid-liquid ratio,Baume and Sulfuric acid,fly ash dosage range;Secondly,orthogonal design test was conducted to study the optimal ratio of sulfur,magnesium oxide binder and the order of compressive strength of each component.Then,based on the optimal ratio,the influence of composite admixture on the setting time,compressive strength and water resistance of the magnesium oxysulfate cement was studied.XRD and SEM were used to further analyze the new composite modified magnesium oxysulfate cement in phase and micromorphology.Finally,the composite modified magnesium oxysulfate cement for the preparation of lightweight cementitious wall panels,its preparation process and the basic performance.The basic ratio effect of raw materials on the compressive strength was studied.The results show that the difference of the basic ratio has a great influence on the compressive strength and setting time.When the ratio is unreasonable,the setting time is longer,the compressive strength is lower and the test specimen is cracked.Through single factor test and orthogonal optimization test,the solid-liquid ratio of 1.2,Baume and Sulfuric acid 30Be °,fly ash content of 30%,citric acid 1.25%is the best reference ratio,and setting time to meet the ordinary silicate setting time requirements.The effects of composite modifiers on the compressive strength,setting time and water resistance of magnesium oxysulfate cement were studied.The results showed that different additives were different effects.Citric acid was used as modifier to improve the strength of magnesium oxysulfate cement and oxalic acid as modifier to shorten the setting time of magnesium oxysulfate cement.Then a single modifier is compounded.According to the oretical research and experimental results,the total content of the composite acid is 2%,and the oxalic acid and citric acid are modified by 1:3(mass ratio),the compressive strength of 28d cement reaches about 72.5 MPa,which is more than twice as much as that of unmodified magnesium oxysulfate cement and 1.5 times of single modified magnesium oxysulfate cement.The setting time is normal to meet ordinary silicon,no pan-frost phenomenon and the softening coefficient of more than 0.95,XRD and SEM analysis showed that a new phase was formed in the composite modified magnesium oxysulfate cement,which mainly consisted of 5Mg(OH)2·MgSO4·7H2O(5·1·7).The formation of a new phase is one of the main reasons for the compressive strength improvement and water resistance of magnesium sulfate cement.The preparation process and basic properties of lightweight partition board were studied.The results show that the composite modified magnesium oxysulfate cement as the binder,EPS polystyrene particles as the filler,glass fiber mesh as a reinforcing material,adding animal protein foaming agent for foaming,after the ingredients mixed,prepared into bulk density 416kg/m3 lightweight partition wall plate,Its performance indicators and test analysis to meet the GB/T23451-2009 "lightweight partition wall construction" requirements.