Development of magnesium silicate hydrate (M-S-H) cements from a low-purity magnesium oxide source

The performance of a low-purity magnesium oxide (magnesia) source for the synthesis of magnesium silicate hydrate (M-S-H) cements was evaluated. Magnesia-rich precursors were produced from a raw magnesite containing significant levels of impurities (e.g. silicon dioxide, aluminium oxide and ferric oxide), which was ground and calcined at different temperatures (600, 650 and 700°C). The alternative precursors were initially characterised by their physical, chemical, mineralogical and hydration properties. Cement pastes were then prepared using the calcined magnesite samples and commercial silica fume and evaluated in terms of mechanical performance (after 3, 7, 28 and 56 days of curing) and microstructure (after 7 and 56 days of curing). The pastes produced with the most reactive samples (calcined at 650°C and 700°C) exhibited compressive strength equivalent to or higher than that of the control mixture (prepared using high-purity commercial magnesia with the same mix proportions). Microstructural characterisation further revealed structural similarities among the M-S-H phases formed in all samples after 56 days of curing. These findings demonstrate the feasibility of using low-value magnesia-rich precursors to produce M-S-H binders through appropriate grinding and/or calcination strategies. Moreover, this study encourages further research on the valorisation of magnesia-rich industrial wastes for the development of more eco-efficient cement-based composites.