Calcination is a common activation method for clays used as supplementary cementitious materials (SCMs). This study explores an ecofriendly and sustainable clay activation approach, namely mechanochemical calcination (MCC), which combines calcination with a high shear grinding process. Two natural mixed layer clays, dominated by kaolinite and illite, along with the respective virgin pure clays (kaolinite and illite), were treated via calcination, mechanochemical activation, and MCC. The study evaluated their mineralogical transformation, microstructure, and compressive strengths. The findings revealed that mechanochemical activation reduced particle size by up to 73% and increased surface area by 72%, particularly in illite-rich clays. MCC further reduced particle size, particularly in clays rich in illite and quartz. MCC enhanced 7 day compressive strength in illite-dominant natural clays and pure illite clays by 6% and 98%, compared to calcination. In contrast, for pure kaolinite, MCC doubled the particle size (from 5 μm in calcined to 10 μm in MCC), reduced reactivity (12% lower bound water), and tripled porosity, resulting in lower compressive strength. Al²⁷ MAS-NMR revealed that MCC increased Al(V) sites in illite from 0% in raw clays to 40% in MCC treated clays. This increase contributed to enhanced strength. In kaolinite, however, calcination increased Al(V) sites, increasing pozzolanic reactivity. Overall, MCC proves to be an efficient activation method for illite-rich natural clays, yielding a 14% increase in compressive strength at 28 days compared to calcination. Future research should consider combinations of calcination and mechanochemical activation parameters to identify the most energy efficient conditions. Emphasis should be placed on energy demand to optimise and transfer laboratory scale conditions (mechanical activation) to industrial applications.
Jayathilakage et al. (Wed,) studied this question.