Development of Magnesium/Calcium Oxalate Cements

Magnesium oxalate cement, a novel alternative to portland cement, can be made at room temperature by reacting dead-burned magnesia and salts of oxalic acid. Since oxalic acid can be made using captured carbon dioxide, oxalate cements may even be carbon negative. However, emissions related with the decarbonation of magnesite at high temperatures make this hard to achieve. This study investigates the effect of replacing magnesia with granulated blast furnace slag on some physical and mechanical properties, as well as the mineralogy and microstructure of oxalate cements. Whewellite and Weddellite are identified when slag is used, in addition to Glushinskite which forms from magnesia. Slag-only mortars undergo faster but less complete reactions and show lower resistance to water than their magnesium oxalate counterparts. An equal-part combination of dead-burned magnesia and slag gives the highest 28-d strength (> 35 MPa), pH~7, and high water resistance.