Title:
Hydration Mechanism of MgO-Nesquehonite Blends
Author(s):
Paula Montserrat-Torres, Barbara Lothenbach and Frank Winnefeld
Publication:
Symposium Paper
Volume:
362
Issue:
Appears on pages(s):
283-291
Keywords:
alternative binder, brucite, cement, eco-friendly, hydrated magnesium carbonate, magnesia, nesquehonite
DOI:
10.14359/51740889
Date:
6/6/2024
Abstract:
High CO2 emissions are associated with the production of Portland cement. To reduce these emissions, alternative binders based on magnesium have been proposed. Magnesium carbonate hydrate cement prepared from MgO and carbonates such as e.g. hydromagnesite (Mg5(CO3)4(OH)2·4H2O) or nesquehonite (MgCO3ˑ3H2O) have the potential to bind carbonates during the hardening process. Such mixes develop adequate compressive strength, in contrast to pure MgO cement. This study investigates the hydration of MgO in the presence of nesquehonite as a carbonate source, a less stable and more reactive magnesium carbonate than hydromagnesite.
MgO pastes with different percentages of nesquehonite were prepared and analyzed with XRD, TGA, and FTIR to characterize the phases formed during hydration. Calorimetry was also used to follow the hydration kinetics up to 7 d. The results revealed that the addition of nesquehonite in MgO-based cements significantly delays the hydration. TGA and XRD analyses confirmed the formation of hydrous carbonate-containing brucite (HCB) in the presence of nesquehonite, characterized by its content of gel water and CO2. FTIR data further supported the presence of carbonate groups in HCB. At least 15 wt% of nesquehonite reacts to form HCB, contributing to the mechanical properties of MgO-based cements.