| Magnesium oxysulfate cement is composed of active magnesium oxide and magnesium sulfate solution MgO-MgSO4-H2O temately cementation material,with light weight,fast setting,high temperature resistance,energy saving and environmental protection characteristics.However,due to the poor water resistance of magnesium oxysulfate cement,it is not widely used in road,civil engineering and other industries,so it is particularly important to improve the performance of magnesium oxysulfate cement.In addition,as a coastal country,China has a coastline of 18000 kilometers.The development of marine engineering is very important for the future development of our country.The ocean is rich in sulfate,chloride ion,magnesium ion and so on,which can erode cement concrete and corrode steel bar.Therefore,it is very important to study the ion erosion resistance of modified magnesium oxysulfate cement while improving the water resistance of magnesium oxysuflate cement.In order to improve the performance of magnesium oxysulfate cement,the basic raw material ratio test was carried out first,and the best comprehensive raw material ratio was selected MgO:MgSO4:H2O=10:1:20.The effects of D-type malic acid on setting time and pH,mechanical properties of magnesium oxysulfate cement were analyzed by adding D-type malic acid modified magnesium oxysulfate cement.The changes of hydration heat release,phase composition,microstructure and pore size distribution of D-type malic acid modified magnesium oxysulfate cement were analyzed by means of hydration heat and XRD,FTIR,SEM,MIP detection equipment.the mechanism of incorporation of D type malic acid modified magnesium oxysulfate cement was systematically analyzed.D-type malic acid can improve the performance of magnesium oxysulfate cement and the optimal content is 0.5(wt.%).After adding 0.5(wt.%)D type malic acid,the compressive strength of magnesium oxysulfate cement increased from 62.4 MPa to 94.2 MPa,and the flexural strength increased from 6.0 to 12.5 MPa;forming a new hydration product 5·1·7 phase,and its dense structure reduced the porosity of magnesium oxysulfate cement.In order to test the water resistance and erosion resistance of magnesium oxysulfate cement,it was immersed in distilled water,sodium sulfate,sodium chloride and sodium hydroxide solution,respectively,the influence of ions on the properties of magnesium oxysulfate cement was analyzed.Experimental results show that magnesium oxysulfate cement has excellent water resistance and sulfate resistance.When soaking distilled water and 3%sodium sulfate solution for 28 d,the softening coefficient is 0.87 and 0.96;Poor resistance of magnesium oxysulfate cement to chloride corrosion,after soaking in 10%sodium chloride solution for 28 d,the compressive strength of magnesium oxysulfate cement decreased to 34.5 MPa;the compressive strength of magnesium oxysulfate cement remains stable when immersed in sodium hydroxide solution of pH(7～11),while when the pH of immersion solution is(12～14),the compressive strength decreases and the softening coefficient is 0.7,0.33,and 0.15,respectively. |
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