Effect of pulverized fuel ash and CO2 curing on the water resistance of magnesium oxychloride cement (MOC)

Abstract 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) 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 2 curing could further improve the performance of the PFA-blended MOC due to the formation of a higher content of amorphous gel.

[1]  Zongjin Li,et al.  The influence of FeSO4 and KH2PO4 on the performance of magnesium oxychloride cement , 2016 .

[2]  Zonghui Li,et al.  Recent Development of Magnesium-Based Cements - Magnesium Phosphate Cement and Magnesium Oxychloride Cement , 2010 .

[3]  F. Glasser,et al.  Synthesis and characterisation of magnesium silicate hydrate gels , 2005 .

[4]  Min Deng,et al.  Effects of MgO-based expansive additive on compensating the shrinkage of cement paste under non-wet curing conditions , 2012 .

[5]  Zongjin Li,et al.  Influences of fly ash on magnesium oxychloride mortar , 2009 .

[6]  Guozhong Li,et al.  Experimental study on urban refuse/magnesium oxychloride cement compound floor tile , 2003 .

[7]  Zongjin Li,et al.  Light-weight wood–magnesium oxychloride cement composite building products made by extrusion , 2012 .

[8]  D. Deng,et al.  THE MECHANISM FOR SOLUBLE PHOSPHATES TO IMPROVE THE WATER RESISTANCE OF MAGNESIUM OXYCHLORIDE CEMENT , 2003 .

[9]  C. Cheeseman,et al.  Development of low pH cement systems forming magnesium silicate hydrate (M-S-H) , 2011 .

[10]  R. Mathur,et al.  Magnesium oxychloride cement concrete , 2007 .

[11]  Chi Sun Poon,et al.  Experimental study on CO2 curing for enhancement of recycled aggregate properties , 2014 .

[12]  Caijun Shi,et al.  Effect of pre-conditioning on CO2 curing of lightweight concrete blocks mixtures , 2012 .

[13]  K. G. Mayhan,et al.  The role of magnesium oxychloride as a fire-resistive material , 1974 .

[14]  J. Kerienė,et al.  Structural, physical and mechanical properties of modified wood–magnesia composite , 2007 .

[15]  Ángel Palomo,et al.  Composition and Microstructure of Alkali Activated Fly Ash Binder: Effect of the Activator , 2005 .

[16]  Waleed H. Khushefati,et al.  Effects of nano and micro size of CaO and MgO, nano-clay and expanded perlite aggregate on the autogenous shrinkage of mortar , 2015 .

[17]  Ángel Palomo,et al.  Alkali-activated fly ashes: A cement for the future , 1999 .

[18]  S. Chatterji,et al.  Mechanism of expansion of concrete due to the presence of dead-burnt CaO and MgO , 1995 .

[19]  E. Sebastian,et al.  Forced and natural carbonation of lime-based mortars with and without additives: Mineralogical and textural changes , 2005 .

[20]  Patrick Dangla,et al.  Impact of accelerated carbonation on OPC cement paste blended with fly ash , 2015 .

[21]  P. Maravelaki-Kalaitzaki,et al.  Sorel's cement mortars: Decay susceptibility and effect on Pentelic marble , 1999 .

[22]  S. Xia,et al.  Studies on the basic compounds of magnesia cement: the thermal behaviour of magnesium oxychlorides , 1991 .

[23]  C. R. Armstrong,et al.  Reactions and Equi ibria in Magnesium Oxych oride Cements , 1976 .

[24]  Haifeng Lu,et al.  Design of additives for water-resistant magnesium oxychloride cement using pattern recognition , 1994 .

[25]  R. L. Berger,et al.  Acceleration of Hydration of Calcium Silicates by Carbon Dioxide Treatment , 1972 .

[26]  Chi Sun Poon,et al.  CO2 curing for improving the properties of concrete blocks containing recycled aggregates , 2013 .

[27]  J. M. Tura,et al.  Cracks in Sorel's cement polishing bricks as a result of magnesium oxychloride carbonatation , 1996 .

[28]  C. Poon,et al.  Materials characteristics affecting CO2 curing of concrete blocks containing recycled aggregates , 2016 .

[29]  C. Cheeseman,et al.  Formation of magnesium silicate hydrate (M-S-H) cement pastes using sodium hexametaphosphate , 2014 .

[30]  Chungkong Chau,et al.  Influence of molar ratios on properties of magnesium oxychloride cement , 2007 .

[31]  Zongjin Li,et al.  Microstructures of magnesium oxychloride , 2008 .

[32]  Jiang Yunsong.  Study of the new type of light magnesium cement foamed material , 2001 .

[33]  Guozhong Li,et al.  The influence of compound additive on magnesium oxychloride cement/urban refuse floor tile , 2008 .