Technical and carbon footprint assessment of mortars derived from CO2 and magnesia recovered from bischofite

Abstract

Bischofite (MgCl₂·6H₂O), the byproduct of salt lake resource extraction, is a useful source for valuable resources. This study investigated the production and utilization of reactive magnesia (MgO) cement (RMC) from bischofite. Synthetic RMC recovered through timed calcination was used in preparing CO₂-cured mortars and compared to samples produced from commercial RMC. The acid neutralization time, an indication of reactivity, of the synthetic RMC from complete calcination indicated a good correlation with the specific surface area. Synthetic RMC-based mortars exhibited higher reaction rates of hydration and carbonation than mortars involving commercial RMC. Furthermore, mortars prepared with synthetic RMC demonstrated higher compressive strengths, attributed to a denser pore structure and enhanced moduli/hardness in interfacial transition zones. The identification of the key factors governing mechanical performance facilitated the regulation of the strength of high-activity RMC-based mortars. The overall CO₂ per MPa of the synthetic MgO-based mortar was 19.7% lower than that for the commercial RMC-based mortar.