Abstract
Damaged structures on coral islands have been spalling and cracking due to the dual corrosion of tides and waves. To ensure easy access to aggregate materials, magnesium potassium phosphate cement (MKPC) and coral sand (CS) are mixed to repair damaged structures on coral islands. However, CS is significantly different from land-sourced sand in mineral composition, particle morphology, and strength. This has a substantial impact on the hydration characteristics and macroscopic properties of MKPC mortar. Therefore, in this study we investigated the compressive strength, interfacial mechanical properties, and corrosion resistance of MKPC CS mortar. Changes in the morphology, microstructure, and relative contents of hydration products were revealed by scanning electron microscope-energy dispersive spectrometer (SEM-EDS) and X-ray diffraction (XRD). The results indicated that the compressive strength increased linearly with the interfacial micro-hardness, and then stabilized after long-term immersion in pure water and Na2SO4 solution, showing excellent corrosion resistance. Compared with MKPC river sand (RS) mortar, the hydration products of CS mortar were an intermediate product 6KPO2·8H2O with a relative content of 3.9% at 1 h and 4.1% at 12 h. The hydration product MgKPO4·6H2O increased rapidly after 7-d curing, with an increased growth rate of 1100%. Our results showed that CS promoted the nucleation and formation of hydration products of MKPC, resulting in better crystallinity, tighter overlapping, and a denser interfacial transition zone. The results of this study provide technical support for applying MKPC mortar as a rapid repair material for damaged structures on coral islands.
概要
目 的
在珊瑚岛礁上, 构筑物因为潮汐和风浪的双重侵蚀作用而损伤严重. 为确保修补有效和取材便利, 人们采用磷酸钾镁水泥和珊瑚砂配制成砂浆对珊瑚岛礁构筑物进行修补. 本文旨在探讨珊瑚砂对磷酸钾镁水泥砂浆的宏细观力学特性、 抗侵蚀性及水化行为的影响规律, 为磷酸钾镁水泥作为快速修补材料在珊瑚岛礁损伤构筑物中应用提供理论基础和技术支撑.
创新点
1. 揭示珊瑚砂对磷酸钾镁水泥砂浆宏细观力学特性和抗侵蚀性能的影响规律; 2. 采用定量分析的方法阐明珊瑚砂对磷酸钾镁水泥水化产物相组成和相对含量的影响规律.
方 法
1. 利用抗压强度测试和显微硬度测试手段分析不同养护龄期下关键因素掺量对磷酸钾镁水泥-珊瑚砂浆宏细观力学特性的影响; 2. 将磷酸钾镁水泥砂浆暴露于Na2SO4溶液中, 分析其在长期浸泡条件下抗压强度的劣化机制及抗盐溶液侵蚀的行为规律; 3. 利用扫描电子显微镜-能谱仪, 揭示不同养护龄期下水化产物相形貌及微结构特征, 结合X射线衍射, 利用绝热法定量分析水化产物相相对含量随养护龄期的变化规律.
结 论
1. 与磷酸钾镁水泥-河砂浆相比, 磷酸钾镁水泥-珊瑚砂浆体的界面显微硬度值更高, 且其界面过渡区平均显微硬度值与抗压强度呈明显的线性关系. 2. 磷酸钾镁水泥-珊瑚砂浆在清水和Na2SO4溶液长期浸泡下的抗压强度保持稳定, 表现出较好的抗Na2SO4溶液侵蚀能力. 3. 珊瑚砂可以在水化初期 (1~12 h) 改善浆体内溶液环境, 抑制KH2PO4的溶解, 并生成絮状络合物6KPO2·8H2O; 在 7~28 d 阶段, 6KPO2·8H2O逐渐溶解并参与反应, 保障MgKPO4·6H2O有足够的时间结晶成核, 使得晶体相互搭接, 形成了致密的板状结构, 进而保障了磷酸钾镁水泥-珊瑚砂浆优异的力学性能和抗侵蚀能力.
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Acknowledgments
This work is supported by the Key Technologies R&D Program of Guangxi Zhuang Autonomous Region (No. GUIKE AB22080073) and the Open Research Program of State Key Laboratory of Geomechanics and Geotechnical Engineering (No. SKLGME021026), China.
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Hao LIU designed the research. Hao LIU and Huamei YANG processed the data. Hao LIU and Houzhen WEI wrote the first draft of the manuscript. Jining YU and Rongtao YAN helped to organize the manuscript. Qingshan MENG and Houzhen WEI revised and edited the final version.
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Hao LIU, Huamei YANG, Houzhen WEI, Jining YU, Qingshan MENG, and Rongtao YAN declare that they have no conflict of interest.
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Effect of coral sand on the mechanical properties and hydration mechanism of magnesium potassium phosphate cement mortar
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Liu, H., Yang, H., Wei, H. et al. Effect of coral sand on the mechanical properties and hydration mechanism of magnesium potassium phosphate cement mortar. J. Zhejiang Univ. Sci. A 25, 116–129 (2024). https://doi.org/10.1631/jzus.A2200389
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DOI: https://doi.org/10.1631/jzus.A2200389
Key words
- Magnesium potassium phosphate cement (MKPC)
- Coral sand (CS)
- Mechanical properties
- Corrosion resistance
- Hydration mechanism