Utilising phlogopite as a supplementary cementitious material (SCM)

The production of ordinary Portland cement (OPC) is the reason for carbon dioxide emissions and high energy consumption, making it important to explore more environmentally friendly ways in concrete production. One effective approach to reducing the environmental impacts of cement is the partial replacement of OPC with supplementary cementitious materials (SCMs). This thesis investigates the potential of phlogopite, a magnesium-rich mica mineral obtained as a mining by-product from Siilinjärvi, Finland, as an SCM in Portland cement-based systems.

To improve its reactivity, phlogopite was examined through mechanical milling and chemical pre-treatment using sulfuric acid (H2SO4) and 3,4-dihydroxybenzoic acid (DHZ), combined with sonication. Cement mortars were prepared with a 20 wt.% replacement of OPC by phlogopite, and compressive strength was measured after 3, 7, and 28 days of curing times.

The results indicate that the incorporation of raw, untreated phlogopite as a SCM hindered the strength development of the mortar specimens. In contrast, disk-milled phlogopite led to an enhancement in mechanical strength compared with the reference samples composed of 100% Portland cement. Additional chemical treatment of phlogopite did not result in further improvements in mechanical performance; however, the strength values remained higher than those observed for mortars containing raw phlogopite.

Overall, mechanically activated phlogopite demonstrates potential as a SCM. The utilization of this mining by-product could contribute to reducing clinker consumption and enhancing the sustainability of cement-based materials.