Hydration and phase conversion of MgO-modified calcium aluminate cement

Abstract

This study evaluated the hydration and phase conversion of MgO-modified calcium aluminate cement (CAC). MgO was used to replace CAC at various dosages (0, 5, 10, 15, and 20 wt%) and the samples were exposed to a 60 °C atmosphere to expedite the conversion of the hydration products in CAC after curing initially at 20 °C. Microstructural analysis was carried out before and after expedited curing using various characterization techniques. During the initial curing, MgO can suppress the phase conversion, hindering the formation of stable phases (i.e., C3AH6 and AH3). After 28 days of expedited curing, a phase conversion can occur, with metastable phases converted to stable phases, due to which a strength reduction can be observed in all samples. Nevertheless, the development of hydrotalcite in samples modified with MgO could lessen the degree of the compressive strength loss. The addition of MgO can maintain the structural integrity before exposure by suppressing the conversion of metastable hydrates and after exposure through the formation of an Mg-Al LDH tetrahedral Al network as a secondary hydration product, maintaining the strength after exposure.