Preparation And Properties Of New Magnesium Cement

To improve and enhance the performance of magnesium oxysulfate cement, this paper has introduced the design of orthogonal tests and mixture experiments so as to do systematic reasearch on strength properties, volume stability, water resistance, acid and alkali resistance of magnesium oxysulfate cement mixed with citric acid and other admixtures. The pore structure of magnesium oxysulfate cement has been studied through the tests of absorptivity value. And the microstructure structure, phase composition, morphology of magnesium oxysulfate cement have been investigated by using X-ray diffraction analysis, scanning electron microscopy and EDS analysis. The reasons of different factors on properties of magnesium oxysulfate cement have been discussed from the aspect of composition and structure respectively.The results showed that citric acid could properly improve the properties of magnesium oxysulfate cement such as strength, water resistance, acid and alkali resistance and volume stability. The properties of magnesium oxysulfate cement could be adjusted by changing the citric acid content, the ratio of MgO/MgSO4and H2O/MgSO4. The optimal mixing proportion was as follows:MgO/MgSO4=1.7, H2O/MgSO4=1, citric acid content=1.3%. The28d compressive strength and flexural strength of this kind of magnesium oxysulfate cement could be up to60.7MPa and12.5MPa respectively. By using the mixed design method, the best mixing proportion of admixtures was made as follows:citric acid65.8%, sucrose17.8%, and boric acid16.4%. The strength and durability of Magnesium oxysulfate cement could be further improved by mixing with modified additives.The tests of absorptivity value showed that the porosity of small capillary pore increased, while average size of capillary pore became smaller, and the cement stone structure could be more dense by using citric acid and other admixtures, thus improving the properties of magnesium oxysulfate cement. We knew from XRD that magnesium oxysulfate cement would generate a new phase composition which was pin rod of crystal by incorporating citric acid and other admixtures through SEM. The new phase has changed the composition and structure, and thus improved the properties of the magnesium oxysulfate cement.The paper has systematically analyzed the effects of MgO/MgSO4, H2O/MgSO4and citric acid on properties of magnesium oxysulfate cement, and revealed the corresponding mechanisms, which are conducive to the further research and application of magnesium oxysulfate cement.