| Magnesium oxysulfate cementitious material has good performance with light weight, good volume stability, flexural strength, fire-resistance.Although the compressive strength of magnesium oxysulfate cementitious material lower than magnesium oxychloride cementitious materials, in its water resistance, environmental protection and without corrosion to steel, active suppression pantothenic frost etc. Magnesium oxysulfate cementitious material has its own unique special in the production of decoration materials have an advantage.In consequence,it is necessary to improve the performance of magnesium oxysulfate cementitious material.First of all, we try an experiemt of basic ratio of magnesium oxysulfate cementitious material at room temperature and found out the good molar ratio of MgO: MgSO4?7H2O, then we mixed with 19 kinds different types of additives based on the benchmark ratio and screened some additives can improve obviously the strength of magnesium oxysulfate cementitious material-citric acid, sodium citrate and sucrose.Optimized admixture content of additives by orthogonal design.In order to reduce micro-cracks and improve the water resistance of magnesium oxysulfate cementitious material,we performed the experiment of inorganic packings.The experimental results indicated that silica fume, fly ash filler not only increase the strength of magnesium oxysulfate cementitious material,but also improve the water resistance of magnesium oxysulfate cementitious material.The paper also discussed the temperature, humidity, age, magnesium oxide fine sulfur oxide and other factors on the impact of magnesium oxysulfate cementitious material strength, these results indicated that controlling the temperature in 20 ~ 25℃and grelative humidity at 60% can increase the strength of magnesium oxysulfate cementitious material. The 7d compressive strength of magnesium oxysulfate cementitious material accessed to 44.5MPa. This article also confirmed that the complex admixture of magnesium oxysulfate cementitious material at room temperature formed a new double salt phase by XRD, DTA, TG test methods.We observed the morphology of complex salt by SEM and found that complex salt is a small needle crystals,this small needle crystals made the complex salt forming good density, and improved the water resistance of magnesium oxysulfate cementitious material.The article also examined simply the hydration mechanism of magnesium oxysulfate cementitious material from the standpoint of thermodynamics and kinetics ,and made a useful exploration for increasing the use of magnesium oxysulfate cementitious material. |
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