Phase Evolution of MgO-Nesquehonite Cements

Abstract

Magnesium-based cements, which combine MgO and nesquehonite (MgCO₃·3H₂O), are promising low-carbon binders which sequester CO₂ and gain strength through the formation of hydrous carbonate-containing brucite (HCB). This study analyses the evolution of solid and liquid phases in MgO-nesquehonite suspensions (0 to 60% nesquehonite by mass, w/s = 10) over a year using XRD, TGA, FTIR, Raman spectroscopy and liquid analysis (pH, ionic composition), and compares them with previously studied paste systems (w/s = 1.25). The results show that HCB is the main hydrate after 28 days, while artinite forms in addition in blends with more than 30% nesquehonite after 91 days, consuming CO₂ from HCB. Calculated saturation indices and the evolution of dissolved Mg and inorganic carbon confirm the dissolution of nesquehonite and the subsequent formation of HCB and artinite. Compared with paste systems, suspensions show faster phase evolution and artinite formation due to the higher water availability and continuous mixing. The findings confirm the metastability of HCB and provide data for the thermodynamic modelling of durable MgO-based binders.