Early Properties of MgO-based Cement for the Stabilization of Kaolinite Clay

Clay-based building materials provide a sustainable alternative to conventional construction materials. Their low mechanical properties can be improved by a sustainable binder, such as MgO-based cement. This study explores the early-age properties of a model system containing kaolinite and MgO-based cement (a mixture of MgO and metakaolin) and compares it to traditional Portland cement stabilization. Sodium hexametaphosphate (NaHMP) and sodium carbonate (Na-carbonate) are added as admixtures to enhance rheology and reactivity. A blend of NaHMP and Na-carbonate results in the fastest setting times (6 h initial set, 15 h final set). NaHMP and Na-carbonate promote M-(A)-S-H and hydrotalcite formation and reduce brucite precipitation. With NaHMP, compressive strengths of 0.9, 3.4, and 5.4 MPa are reached for the poured systems after 1, 3, and 7 days, respectively. The synergy of MgO-based cement, clay minerals, and admixtures enables effective stabilization for poured earth applications with shortened setting times and enhanced early strength.