ISSN 0862-5468 (Print), ISSN 1804-5847 (online) 

Ceramics-Silikáty 64, (1) 75 - 83 (2020)

Qing Huang 1,2,3, Ying Li 1,2, Jing Wen 1, 2, Weixin Zheng 1,2, 3, Chenggong Chang 1, 2, Jinmei Dong 1, 2, Danchun A 1,2, 3, Xueying Xiao 1, 2, Yuan Zhou 1 , 2
1 Key Laboratory of Comprehensive and Highly Efficient Utilization of Salt Lake Resources, Qinghai Institute of Salt Lakes, Chinese Academy of Sciences, No. 18, Xinning Road, Xining 810008, P.R. China
2 Key Laboratory of Salt Lake Resources Chemistry of Qinghai Province, No. 18, Xinning, Xining 810008, P.R. China
3 University of Chinese Academy of Sciences, No. 19, Yuquan Road, Beijing 100049, P.R. China

Keywords: Magnesium oxychloride cement, Water resistance, Ethyl silicate, Micro structure

In this paper, fly ash (FS), phosphoric acid (H₃PO₄), ferrous sulfate (FeSO₄·7H₂O) and ethyl silicate (TEOS) were incorporated to devote effort for the further improvement of the water resistance of magnesium oxychloride cement (MOC). The strength retention coefficient was tested to evaluate the water resistance of the MOC, in which the addition of FS + H₃PO₄ + FeSO₄·7H₂O + TEOS resulted in a remarkable improvement. The characterisation of the hydration products before and after the water immersion was carried out using X-ray diffraction (XRD), a thermogravimetric (TG) analysis, Fourier-transformed infrared spectroscopy (FTIR) and a scanning electron microscope (SEM). Through the XRD, TG and FTIR analysis, the results showed that the addition of FS + H₃PO₄ + FeSO₄·7H₂O + TEOS resulted in the generation of the amorphous phase during the water immersion. This amorphous gel was identified as a mixture of a magnesium-chloride-silicate-hydrate gel (M-Cl-S-H gel) and an insoluble magnesium-chloride-hydrate gel (M-Cl-H gel) by Energy Dispersive Spectrometer (EDS). The generation of the insoluble M-Cl-S-H gel and M-Cl-H gel and the densification of the microstructure contributed to the valuable and long-term improvement of the water resistance in the MOC. Then the transformation of the morphology might be due to the interaction performance and superposed effect of FS, H₃PO₄, FeSO₄·7H₂O and TEOS.

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doi: 10.13168/cs.2019.0051
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