Influence of MgO/MgCl₂ molar ratio on phase stability of magnesium oxychloride cement

Abstract

Formation, solution and phase change of hydration products in MgO-MgCl₂-H₂O system was studied with thermodynamics method, and resistance to water immersion and phase change of magnesium oxychloride cement with different MgO/MgCl₂ molar ratio was experimented. The results show that pH value of immersion solution of cement paste has a remarkable influence on phase stability of hydration products. A higher pH value leads to a lower solubility and a better phase stability of hydration products. When the solution pH value is higher than 10.37, the precipitation of much Mg(OH)₂ crystal induces a worse phase stability of hydration products. With the increasing MgO/MgCl₂ molar ratio (lower than 6), the more amount of MgO in the hydration products enhances the alkalinity of solution and the phase stability is improved. However, when the MgO/MgCl₂ molar ratio is higher than 6 and the excessive MgO exsits in the hydration products, the cement paste may be damaged by the excessive crystallization stress of a great deal of Mg(OH)₂ formation.

Keywords

magnesium oxychloride cement / molar ratio / phase stability / hydration reaction

References

[1] Cui C., Ma B., Cui K., Suen W. Study on Hydration Mechanism and Kinetics of Magnesium Oxychloride Cements[J]. Journal of Wuhan University of Technology, 1994, 16(2): 37-41.

[2] Zhang C., Deng D. Research on the Water-resistance of Magnesium Oxychloride Cement I: the Stability of the Reaction Products of Magnesium Oxychloride Cement in Water[J]. Journal of Wuhan University of Technology, 1994, 9(3): 51

[3] Zhang C., Deng D. The Formation Mechanism of the Hydrate Phases in Magnesium Oxychloride Cement[J]. Cement and Concrete Research, 1999, 29: 1 365

[4] Ji B., Xia S. Dissolution Behavior of Oxychlorides in Water[J]. Chinese Journal of Applied Chemistry, 1995, 12(3): 43-47.

[5] Zhang C., Deng D. Research on the Water Resistance of Magnesium Oxychlride Cement and its Improvement[J]. J Chin Ceram Soc, 1995, 23(6): 673-679.

[6] Sorell C A, Armstrong C R. Reactions and Equilibria in Magnesium Oxychloride Cements[J]. J Am Ceram Sa, 1976, 59

[7] Zhang Zhenyu, Dai Changlu, Zhang Quanchang, et al. Research on Formation Mechanism of as 5-phase and as 3-phase[J]. Chinese Science (B), 1991, (1): 82–89

[8] Matkovic B., Popvic S., Rogic V., . Reaction Products in Magnesium Oxychloride Cement Pastes System MgO-MgCl₂-H₂O[J]. J Am Ceram Soc, 1977, 60(11–12): 504-507.