Hydration and strength development of MgO-nesquehonite-metakaolin binders

This study evaluates the feasibility of blending metakaolin into MgO-nesquehonite binders. During hydration, hydrotalcite and M-(A-)S-H phases were formed alongside hydrous carbonate-containing brucite (HCB). At high nesquehonite contents (≥ 22 wt%), partial transformation to hydromagnesite/dypingite might occur over time, reducing the carbonate fraction in HCB. Ex-situ leaching results showed low pH values of 10–10.5 in the MgO-nesquehonite-metakaolin binders, which limited metakaolin dissolution (56–72 wt% of added metakaolin remaining unreacted after 91 days). Nevertheless, the mortars with a water-to-cement ratio of 0.71 achieved compressive strengths of 25–30 MPa at 2 days and 35–45 MPa after 28 days. The CO 2 originally present in nesquehonite was fully sequestrated within the binders, and the total CO 2 content increased slightly over time, indicating additional CO 2 uptake from the atmosphere. Overall, up to 18 g of CO 2 could be sequestrated into 100 g of dry cement.