Improving the Sustainability of Magnesium Oxalate Cements Using Clay and Calcium Sulfoaluminate Clinker

Magnesium oxalate cement (MgOx) is an alternative binder that forms through the acid–base reaction between dead-burned magnesium oxide (MgO1500) and an acid salt containing oxalate ions. Previously, industrial wastes were used to replace MgO1500, and fly ash was used to produce oxalate acid salt. In an attempt to further reduce the carbon footprint of MgOx and use more abundant starting materials, this study used a calcium sulfoaluminate cement (CSA) clinker in place of MgO1500 and a natural, clayey soil to produce oxalate acid salt. The mineralogy and microstructure of pastes were studied, as well as the strength development of mortars. Although full replacement of MgO1500 with CSA yielded samples with 28-d compressive strength ∼30 MPa, it reduced ultimate pH from ∼9 to ∼5, shortened setting times, and negatively impacted strength retention after immersion in water. An equal-part mixture of MgO1500 and CSA gave optimal results. Glushinskite was detected as the main reaction product. No ettringite formed from ye’elimite in CSA due to the low pH of the system.