Effect of free CaO content on the phase composition of magnesium oxychloride cement

IF 13.1 1区工程技术 Q1 CONSTRUCTION & BUILDING TECHNOLOGY Cement & concrete composites Pub Date : 2025-03-01 Epub Date: 2024-12-22 DOI:10.1016/j.cemconcomp.2024.105906

Yu Cui, Zanqun Liu, Ju Huang, Wei Zhang, Yi Wang, Jiahui Zhu, Dehua Deng

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Abstract

The free CaO (FC) in light-burnt MgO due to the impurity of magnesite ores cannot be avoided, and causes the declination of properties of magnesium oxychloride cement (MOC). In order to clearly explain the declination mechanism of MOC properties due to FC, the effect of FC contents on the formation of phase compositions and the compressive strength of MOC pastes were studied in detail. The findings revealed that the addition of FC sharply increased the pH value of MOC pastes, and changed the final compositions of the hardened MOC pastes. Specifically, FC contents more than 4 % could cause the formation of phase 5 by the phase 3 transformation at MgO/MgCl₂/H₂O molar ratio of 3:1:11, and FC contents more than 2 % could lead to the formation of phase Mg(OH)₂ by phase 5 transformation at MgO/MgCl₂/H₂O molar ratio of 5:1:13. Consequently, the transformation of phase compositions caused the remarkable declination of compressive strength of MOC pastes. The content of FC should be given attention in the MgO/MgCl₂/H₂O molar ratio, and the permissible contents of FC should be limited to less than 4 % and 2 % relevant to the MgO/MgCl₂/H₂O molar ratios at 3:1:11 and 5:1:13, respectively.

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游离CaO含量对氯氧镁水泥相组成的影响

轻烧MgO中的游离CaO （FC）由于氧化镁矿石的杂质而无法避免，导致氯化氧镁水泥（MOC）性能下降。为了更清楚地解释FC对MOC性能的影响机理，详细研究了FC含量对MOC膏体相组成形成和抗压强度的影响。结果表明，FC的加入使MOC膏体的pH值急剧升高，并改变了MOC硬化膏体的最终组成。其中，当FC含量大于4%时，MgO/MgCl2/H2O摩尔比为3:1:11时，可以通过3相转化形成5相；当FC含量大于2%时，MgO/MgCl2/H2O摩尔比为5:1:13时，可以通过5相转化形成Mg(OH)2相。因此，相组成的变化导致MOC膏体抗压强度的显著下降。在MgO/MgCl2/H2O摩尔比中应注意FC的含量，在MgO/MgCl2/H2O摩尔比为3:1:11和5:1:13时，FC的允许含量应限制在4%和2%以下。

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来源期刊

Cement & concrete composites 工程技术-材料科学：复合

CiteScore

18.70

自引率

11.40%

发文量

459

审稿时长

65 days

期刊介绍： Cement & concrete composites focuses on advancements in cement-concrete composite technology and the production, use, and performance of cement-based construction materials. It covers a wide range of materials, including fiber-reinforced composites, polymer composites, ferrocement, and those incorporating special aggregates or waste materials. Major themes include microstructure, material properties, testing, durability, mechanics, modeling, design, fabrication, and practical applications. The journal welcomes papers on structural behavior, field studies, repair and maintenance, serviceability, and sustainability. It aims to enhance understanding, provide a platform for unconventional materials, promote low-cost energy-saving materials, and bridge the gap between materials science, engineering, and construction. Special issues on emerging topics are also published to encourage collaboration between materials scientists, engineers, designers, and fabricators.