Enhancing magnesium oxalate cements with copper slag and silica fume

Magnesium oxalate cement is an alternative binder made by reacting dead-burned magnesia and oxalic acid salts. Dead-burned magnesia, which has a high carbon footprint, was replaced at different levels (25–100 %) with copper slag, as a source of iron and thus a reactive component, or silica fume, as an inert or low-reactivity component. The powder mixtures contained ∼25–35 % oxalate, by mass. Physical and mechanical properties were investigated as well as changes in the mineralogy and morphology of paste and mortar specimens. Replacement of up to 50 % of dead-burned magnesia yielded strong (> 30 MPa) and water-resistant mortars with extended setting times, for mixtures with lower oxalate content. Mixtures with higher oxalate content and those without any dead-burned magnesia suffered significant strength loss in water. When copper slag was used, humboldtine, an iron oxalate, formed instead of or in addition to glushinskite, the main reaction product of magnesium and oxalate ions. Silica fume did not yield any crystalline reaction products.