A discussion of the papers "Impact of hydrated magnesium carbonate additives on the carbonation of reactive MgO cements" and "Enhancing the carbonation of MgO cement porous blocks through improved curing conditions", by C. Unluer & A. Al-Tabbaa

This paper is a discussion of two recent papers by Unluer & Al-Tabbaa which analysed accelerated carbonation of reactive MgO blocks. We suggest that the authors have incorrectly analysed key data, leading to overstated claims of MgO carbonation. Based on the reassignment of their X-ray diffraction data, it is proposed that little MgO carbonation occurred in the samples discussed in those papers, with CaCO3 instead forming during accelerated carbonation. We also draw attention to the thermodynamic instability of nesquehonite under ambient conditions, which calls into question the long-term stability of these binders.