Simulation of the properties of MgO-MgfCl{sub 2}-H{sub 2}O system by thermodynamic method

Journal Article · Sun Feb 15 00:00:00 EST 2015 · Cement and Concrete Research

DOI:https://doi.org/10.1016/J.CEMCONRES.2014.11.006· OSTI ID:22475484

Zhou, Zhong; Chen, Huisu ^[1]; Li, Zongjin ^[2]; Li, Huajian ^[3]

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1. Jiangsu Key Laboratory of Construction Materials, School of Materials Science and Engineering, Southeast University, Nanjing 211189 (China)
2. Department of Civil and Environmental Engineering, Hong Kong University of Science and Technology, Clear Water Bay, Kowloon (Hong Kong)
3. Railway Engineering Institute, China Academy of Railway Science, Beijing 100081 (China)

Magnesium oxychloride cement (MOC) has been investigated by many researchers who have studied its hydration products and properties. Previous works mainly concentrated on experimental studies. This study uses a thermodynamic approach to understand the formation conditions of two major hydration products of MOC, Mg{sub 3}(OH){sub 5}Cl · 4H{sub 2}O (phase 5) and Mg{sub 2}(OH){sub 3}Cl · 4H{sub 2}O (phase 3) at room temperature. The hydration reaction equilibrium of MOC phases has been predicted by using the geochemistry speciation code PHREEQC together with the extended ‘Pitzer.dat’ database. The results show that the formation of the hydration products are controlled by MgCl{sub 2} concentration, activity of H{sub 2}O and pH values of the system. The equilibrium of solid phase diagram, the solubility of different hydration phases are consistent with those results obtained from experimental studies, which validates the thermodynamic model. The phase diagram provides qualitative insights on the synthesis of pure phase 3 and phase 5. For MgO-MgCl{sub 2}-H{sub 2}O system, the minimum MgCl{sub 2} concentration for phase 5 and phase 3 to form are 1.47 mol · kg{sup −} {sup 1} and 2.25 mol · kg{sup −} {sup 1}, respectively. Increasing water volume can result in the transformation from phase 5 and phase 3 to brucite. Additionally, the stability analysis suggests that phase 5 prefers to formation at a higher condition of the a{sub Mg}2 +, pH and a{sub H2O} as compared to the phase 3. Phosphate can significantly influence the hydration products composition of MOC during hydration but no new phosphate appears. - Highlights: • A thermodynamic database was established for magnesium oxychloride cement system on the basis of Pitzer.dat. • Thermodynamic behaviors of magnesium oxychloride cement hydration was modeled. • Calculated phase diagram of magnesium oxychloride cement was plotted.

• OSTI ID: 22475484
• Journal Information: Cement and Concrete Research, Vol. 68; Other Information: Copyright (c) 2014 Elsevier Science B.V., Amsterdam, The Netherlands, All rights reserved.; Country of input: International Atomic Energy Agency (IAEA); ISSN 0008-8846
• Country of Publication: United States
• Language: English

Related Subjects

75 CONDENSED MATTER PHYSICS
SUPERCONDUCTIVITY AND SUPERFLUIDITY
CEMENTS
COMPUTERIZED SIMULATION
CONCENTRATION RATIO
GEOCHEMISTRY
HYDRATION
MAGNESIUM
MAGNESIUM CHLORIDES
MAGNESIUM OXIDES
MOLYBDENUM CARBIDES
OXYCHLORIDES
P CODES
PH VALUE
PHASE DIAGRAMS
PHOSPHATES
SOLIDS
SOLUBILITY
SYNTHESIS
TEMPERATURE RANGE 0273-0400 K