Research On Modification And Composite Technology Of Magnesium Oxysulfate Cement

Magnesium oxysulfate cement is the gas hardness cementitious material,which is formed by hydration reaction from light-burned magnesia powder,magnesium sulfate and water.It has excellent properties such as light weight,low alkalinity,strong adhesion and fire resistance,which has been widely used in decorative materials,mobile board houses,fire door panels,lightweight insulating wall panels,transportation facilities and other fields.However,the application and development of magnesium oxysulfate cement in civil engineering have been limited by their low mechanical strength and poor water resistance.In order to improve its deficiency,the modification and composite of magnesium oxysulfate cement materials have been studied in this paper.The mechanical strength,water resistance and volume stability as the main indicators were used to explore the effect of different raw material ratios on the properties of magnesium oxysulfate cement in these experiments.The explored ranges ofα-Mg O/Mg SO₄ molar ratio and water to binder ratio are fixed at 8:1-11:1 and 0.47-0.50.Increasing the ratio of raw materials appropriately is conducive to the improvement of the performance of magnesium oxysulfate cement.When the molar ratio ofα-Mg O/Mg SO₄and the ratio of water to binder are 10:1 and 0.49,the performance of magnesium oxysulfate cement is the best.The flexural strength and compressive strength are respectively 6.76 MPa and 31.65 MPa,and the softening coefficient is 0.41.In this research,sodium gluconate,tartaric acid and citric acid are used as additives to modify magnesium oxysulfate cement.All three additives can significantly improve the mechanical strength and water resistance of magnesium oxysulfate cement.The order of modification effect is citric acid>tartaric acid>sodium gluconat.The flexural strength and compressive strength of the modified magnesium oxysulfate cement can be increased to22.1 MPa and 90.9 MPa respectively.And the softening coefficient is 0.91.The mineral admixture fly ash and silica fume give full play to the filling of micro-aggregates,which can improve the mechanical strength of magnesium oxysulfate cement materials and reduce the volume shrinkage rate,but they cannot effectively improve the water resistance.The effect of silica fume on magnesium oxysulfate cement is better than that of fly ash.When the addition of silica fume is 5%,flexural strength and compressive strength of magnesium oxysulfate cement are increased to 13.1 MPa and 55.18 MPa respectively.The experiment also studied the effect of composite additive on the properties of magnesium oxysulfate cement.Through orthogonal experiment,the optimal mixing ratio is determined as follows:15%fly ash,10%silica fume,0.5%citric acid and 1%tartaric acid.With this mixture ratio,the flexural strength and compressive strength are respectively27.9 MPa and 75.5 MPa respectively,and the softening coefficient reaches 0.86.With the evaluation indexes of thermal conductivity,density and mechanical strength,the effect of different addition amounts of silica aerogel particles on the properties of magnesium oxysulfate cement materials are discussed.The thermal conductivity,density and mechanical strength of magnesium oxysulfate cement gradually decrease with the increasing of the aerogel.When the addition of aerogel is 10%,the thermal conductivity is0.26 W/（m·K）,the density is 1290 kg/m³,the flexural strength and compressive strength are 6.95 MPa and 12.43 MPa,respectively.