Effect of pulverized fuel ash and CO{sub 2} curing on the water resistance of magnesium oxychloride cement (MOC)

Journal Article · Sat Jul 15 00:00:00 EDT 2017 · Cement and Concrete Research

DOI:https://doi.org/10.1016/J.CEMCONRES.2017.03.005· OSTI ID:22697117

He, Pingping; Tsang, Daniel C.W.

This paper presents a study on the use of pulverized fuel ash (PFA) to improve the water resistance of magnesium oxychloride cement (MOC). Strength retention coefficients and volume stability were tested to evaluate the water resistance of MOC, in which the addition of PFA resulted in a remarkable improvement. The characterization of hydration products before and after water immersion was carried out using quantitative X-ray diffraction (QXRD), thermogravimetric (TG), Fourier-transformed infrared spectroscopy (FTIR) and scanning electron microscope (SEM). With the Q-XRD analysis, it was shown that the addition of PFA could result in the great increase of the amount of amorphous phase during air curing. This amorphous gel was identified as a mixture of magnesium-chloride-silicate-hydrate gel (M-Cl-S-H gel) and magnesium-chloride-hydrate gel (M-Cl-H gel) by elemental mapping scanning. It suggested that PFA could not only react with MOC to form M-Cl-S-H gel, but also change the morphology of magnesium oxychloride. The generation of insoluble M-Cl-S-H gel and M-Cl-H gel and densification of the microstructure contributed to the improvement of the water resistance of MOC. The MOC mortar expanded during air curing due to the hydration of excess MgO. Water immersion led to more expansion of MOC mortar as a result of the continuously hydration of excess MgO and the formation of Mg(OH){sub 2}. Adding PFA could increase the expansion of MOC mortar during air curing, which may because the amorphous gel could remain more water and benefit to the hydration of MgO. While, the addition of PFA could decrease the expansion of cement mortar during water immersion perhaps due to the reduction of the content of excess MgO and the insoluble amorphous-gel-layer that protect the MgO from hydration. Moreover, CO{sub 2} curing could further improve the performance of the PFA-blended MOC due to the formation of a higher content of amorphous gel.

• OSTI ID: 22697117
• Journal Information: Cement and Concrete Research, Vol. 97; Other Information: Copyright (c) 2017 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

36 MATERIALS SCIENCE
AMORPHOUS STATE
CARBON DIOXIDE
CEMENTS
FLY ASH
FOURIER TRANSFORM SPECTROMETERS
FOURIER TRANSFORMATION
GELS
HYDRATES
HYDRATION
INFRARED SPECTRA
MAGNESIUM OXIDES
MIXTURES
MOLYBDENUM CARBIDES
OXYCHLORIDES
PULVERIZED FUELS
SCANNING ELECTRON MICROSCOPY
SILICATES
THERMAL GRAVIMETRIC ANALYSIS
WATER
X RADIATION
X-RAY DIFFRACTION