Scholarly record

FLY ASH AS AN ALTERNATIVE SILICA SOURCE IN MAGNESIUM SILICATE HYDRATE CEMENT

Martina Zaleska, Milena Pavlikova, Adam Pivak, Zbysek Pavlik, Ondrej Jankovsky

Abstract

In an effort to develop binders with a reduced environmental impact, magnesium silicate hydrate (MSH) cement has recently attracted considerable attention. This binder belongs to the family of magnesium-based cements; however, unlike magnesium sulphate and magnesium oxychloride cements, it is classified as a hydraulic cement. It forms through the reaction of reactive magnesium oxide with silica sources in the presence of water, producing magnesium silicate hydrate (MSH) gel. Caustic-calcined magnesite, typically produced at lower calcination temperatures than Portland cement clinker, is commonly used as the MgO source. This study explores the potential of fly ash (FA) as a partial substitute for amorphous silica (AS) in MSH cement systems. Amorphous coagulated silica was used as the primary silica source, while FA from a thermal power plant was investigated as an alternative source of reactive silica to further reduce the carbon footprint of the binder system. The raw materials were first comprehensively characterised in terms of their chemical and physical properties. MSH-based samples were subsequently prepared with FA incorporated at dosages of 5, 10 and 20 wt.%, corresponding to the replacement of 10, 20 and 40 wt.% of amorphous silica, respectively. The hardened samples were evaluated in terms of their basic structural and mechanical properties. The partial substitution of AS with FA had little effect on porosity, except for the mixture with the highest replacement level (20 wt.%). However, the incorporation of FA led to a reduction in mechanical performance, particularly at this highest replacement level. These findings contribute to a better understanding of the behaviour and potential of this type of binder system.

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