Characterization of Mg components in reactive MgO - Portland cement blends during hydration and carbonation

A carbonated binder system containing reactive MgO (r-MgO) and Portland cement (PC) has the potential to provide sufficient mechanical properties and reduce carbon the footprint. However, the understanding of the chemistry of hydration and carbonation of the r-MgO-PC system remains unclear. The purpose of this study is to characterize the Mg components that form blends of r-MgO and PC during hydration and carbonation. Paste specimens of r-MgO and PC with r-MgO replacement levels from 10% to 90% were cast, carbonated and examined. Experimental observations reveal that: (1) nesquehonite only occurs in the carbonated r-MgO-PC paste with r-MgO replacement ≥ 60%; (2) an amorphous phase of hydrated Mg carbonate was identified in the carbonated paste with 50% r-MgO replacement; and (3) hydrotalcite and magnesium silicate hydrate are major hydration products of r-MgO during the hydration of the paste containing 30% and 40% r-MgO, which are expected to be the precursors of amorphous hydrated Mg carbonate.