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Effect of Active Magnesia on the Properties of Cementitious Binders

Published online by Cambridge University Press:  10 December 2012

Jing Zhu ,
Nan Ye ,
Jianwen Liu ,
Yalin Li  and
Jiakuan Yang
Jing Zhu
Affiliation:
School of Environmental Science and Engineering, Huazhong University of Science & Technology, Wuhan 430074, China
Nan Ye
Affiliation:
School of Environmental Science and Engineering, Huazhong University of Science & Technology, Wuhan 430074, China
Jianwen Liu
Affiliation:
School of Environmental Science and Engineering, Huazhong University of Science & Technology, Wuhan 430074, China
Yalin Li
Affiliation:
School of Environmental Science and Engineering, Huazhong University of Science & Technology, Wuhan 430074, China
Jiakuan Yang
Affiliation:
School of Environmental Science and Engineering, Huazhong University of Science & Technology, Wuhan 430074, China
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Abstract

Reactive magnesium oxide (magnesia, MgO) was produced by calcining magnesite at comparatively low temperature, less than 800 ℃C. The reactive MgO and fly ash were used as additives to cementitious binder. The reactive MgO-ordinary Portland cement-fly ash is referred to as MgO-OPC-FA cement in further. The hydration expansion effect of active magnesia on the properties of cementitious binder in different mixing ratio was investigated. It is known that the “dead burnt” MgO reacts with water very slowly, which causes the expansion after the solidification of cement. Therefore, the MgO content in ordinary cement is commonly restricted to less than 5%. Effects of reactive MgO on the expansion properties of the cementitious binders were studied. Hydrated products of reactive MgO cements were investigated by X-ray diffraction (XRD) and Scanning electron microscope (SEM) analysis. The MgO-OPC-FA cement was sound, although the content of reactive MgO in cement was about 8 wt. %. Reactive MgO was hydrated at early age in 24 hours, thus causing rapid expansion. Mg(OH)2appeared on initial stage of cement hydration for active magnesia. The hydration rate of active magnesia was not equal to that of the dead burnt magnesia. The hydration of reactive MgO has a negative effect on the mechanical properties of reactive MgO-ordinary Portland cement-fly ash system, in spite of the inhibitive effect of the expansion of MgO hydration produced by fly ash. Our results shed light on the potential utilization of reactive MgO in the manufacturing of cementitious binders.

Keywords

compositeadditivesmicrostructure
Type
Articles
Information
MRS Online Proceedings Library (OPL) , Volume 1488: Symposium 7B – Concrete with Smart Additives and Supplementary Cementitious Materials , 2012 , imrc12-1488-7b-056
Copyright
Copyright © Materials Research Society 2012 

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References

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