水化硅酸镁体系对氯氧镁水泥基材料耐水性的影响及机理研究

Magnesium oxychloride cement has many advantages like quick hardening, high strength, fire resistance, energy saving and waste consuming. But it is limited to be applied in many areas because of its disadvantages such as halogenation, efflorescence and poor water resistance. To improve these properties, this project will modify the magnesium oxychloride cement by magnesium silicate hydrate system. The activity of the raw materials and the effectiveness of the hydration accordingly will be determined. The composition of the hydration products and the relationships among them will be investigated. Modified magnesium oxychloride cement will be prepared and its basic property will be tested. The variation of the hydration product under different ratio of ingredient and curing time will be studied to determine the factor of the stability of the cement system. The MgO-MgCl2-SiO2-H2O quaternary equilibrium system will be established. Based on the dissolution characteristics and phase transmission equilibrium, the water resistance property of the hydration products with different microstructures will be clarified, and the mechanisms of improving the water resistance of magnesium oxychloride cement modified by magnesium silicate hydrate system will be investigated. Results of this project will provide valuable reference and experiment data for industrial production of modified magnesium oxychloride cement based materials, and lay the foundations for the practical application of magnesium oxychloride cement based materials with modification by magnesium silicate hydrate system.

气硬性氯氧镁水泥具有快硬、高强、耐火、节能、利废等优点，但因返卤、泛霜、翘曲和耐水性差等缺点使其应用领域严重受限。为了改善这些不足，本课题拟利用水硬性的水化硅酸镁体系对其进行改性。测定原材料中不同活性氧化镁和氧化硅含量条件下改性氯氧镁水泥体系的水化有效程度，水化产物之间的作用关系，制备系列水化硅酸镁改性氯氧镁水泥并测试其基本性质。同时研究不同配比条件下水化产物随养护龄期的变化规律以及体系安定性的影响因素，确定MgO-MgCl2-SiO2-H2O四元体系的平衡关系；探明水化硅酸镁体系对于氯氧镁水泥基材料耐水性的影响及作用机理。结合水化产物在不同水环境下的溶蚀特性及相转化平衡，明晰不同配比条件下不同微观特性水化产物的耐水特性，研究水化硅酸镁体系提高氯氧镁水泥基材料耐水性的作用机理。项目成果将为工业生产改性氯氧镁水泥提供相关数据及理论依据，同时为水化硅酸镁改性氯氧镁水泥基材料的实际应用奠定基础。

氯氧镁水泥（Magnesium Oxychloride Cement，MOC）具有快硬、高强、质轻、耐磨等优势，但遇水发生分解，导致强度严重下降，限制了其广泛应用。水化硅酸镁（Magenisium Silicate Hydrate，M-S-H）水泥微观结构致密，为水硬性胶凝材料。本研究将二者进行复合，通过硅灰（Silica fume, SF）对MOC进行改性，目的在于在水环境下，使SF能够和MgO与水反应生成M-S-H，填补MOC孔隙降低水化产物分解，提升MOC浸水强度。.研究先通过加入化学合成M-S-H凝胶的方式验证M-S-H凝胶对MOC体系影响作用。结果表明，28d养护龄期时，掺入M-S-H凝胶可以将MOC的软化系数由0.4提高至0.7以上。TEM下可以明显看出，合成M-S-H凝胶将MOC水化产物进行捆绑包覆，从而使水化产物在水中保持整体结构增强其浸水强度。.随后通过加入SF并寻找最优配比。引入外加剂六偏磷酸钠（SHMP）后，通过设计正交实验并采用多元回归方式对对因变量（软化系数）与自变量（SF、外加剂SHMP）进行数学建模分析。结果表明，SF掺量1 wt.%，SHMP掺量2 wt.%时软化系数最高，其28d耐水系数可达到1.03。多元回归模型可以通过数学角度对MOC耐水性的影响因素进行评判，结果表明SHMP对MOC耐水性改善效果较为明显，并且SF与SHMP对MOC耐水性的提高有协同作用。.同时采用多种手段对SF改性MOC的水化产物进行测试。结果表明：XRD对凝胶相与晶体相共存时不能进行良好表征，凝胶相容易被晶体相的峰所掩盖；TG/DSC，FT-IR及TEM结果均表明没有M-S-H凝胶相生成；压汞法测试孔隙率表明，孔隙率与软化系数呈现较为明显的负相关关系，较小掺量的SF（<2 wt.%）对MOC孔隙率的改性作用更佳；通过SEM/EDS观察水化产物的微观形貌，表明说明SF的加入不仅有物理填充孔隙作用，还可以改变MOC的形貌的作用。SF的加入将部分水化产物的针棒状形貌改变为凝胶状，提高水泥致密性，从而增强MOC抗水性能。