Preperation And Modification Of The Foamed Magnesium Oxysulfate Cementitious Material

Foamed magnesium oxysulfate cement is a lightweight material based on magnesium oxysulfate cement.It has the characteristics of heat preservation,fire retardant and weak corrosion of steel bars.However,its shortcomings poor mechanics and water resistance limit its use.In this paper,reinforced modification,hydrophobic and compound modificationare are studied,preparing lightweight,high-strength and water-resistant foamed magnesium oxysulfate cement.Dry density,compressive strength,softening coefficient,and pore structure as indicators,the inorganic acid salt(sodium dihydrogen phosphate)and organic acid(malic acid,malonic acid,and gluconic acid)were investigated for foamed magnesium oxysulfate cement.The results show that when the amount of sodium dihydrogen phosphate is 0.9 wt%,the maximum compressive strength and softening coefficient reach 3.7582 MPa and 0.81.When the addition amounts of malic acid and malonic acid are 0.9 wt% and 0.6 wt%,the maximum compressive strength is 4.013 MPa and 3.662 MPa,and the softening coefficients are 0.85 and 0.631.The above modifiers can optimize the cell structure.The addition of gluconic acid will increase bubble breaking and connected porosity.Although it will increase mechanical and water resistance,it is not suitable for the system.Organic acids promote the growth of517 crystal phase in the form of screw dislocation.The combined modification of sodium dihydrogen phosphate and malic acid is better than the single modification,the optimal combination is 1.2,sodium dihydrogen phosphate: malic acid is 2: 1.Dry density,pore structure,and water absorption were used to investigate the effects of sodium stearate,bisethylene stearate,and potassium methyl silicate on the foamed magnesium oxysulfate cement.The results show that: both sodium stearate and diethylene stearamide contain long carbon chains and the system has good compatibility,which can optimize the cell structure.The water absorption rate decreases greatly with the increase of the amount of hydrophobic agent added,when the amount of sodium stearate added was 2.1 wt%,the rate of decrease in water absorption was 67.69%.The addition of potassium methylsilicate will loosen the cell structure,increase the dry density and will not greatly reduce the water absorption rate.The hydration products of the samples added with the above hydration products did not change,and the compressive strength and softening coefficient could not be increased.Sodium stearate was selected as the quantification,and the effects of different amount of reinforcing agents on the dry density,compressive strength and softening coefficient,pore structure and water absorption of foamed magnesium oxysulfate cement were investigated.The results show that the composite modifier can greatly increase the compressive strength and softening coefficient,reduce the water absorption,and the performance is better than that of the single-doped modifier.The aspect ratio of the 517 crystal phase is reduced and the structure is more dense,hydrated product is hydrophobic.