Impact of clay calcination method on the physicochemical properties of limestone calcined-clay cement

Calcined clay presents a promising future for the industry, but understanding how calcination methods affect its properties remains a challenge. This study assesses laboratory soak and flash calcination methods on four natural clays by evaluating and comparing physicochemical properties upon calcination. The results show negligible impact by the calcination method for calcined samples compared at equivalent dehydroxylation degree and particle size; said impact is lower than the clays' kaolinite content and secondary phases. Two flash-calcined clays demonstrated slower early-age (< 3 hours) reaction kinetics than their soak-calcined counterparts, with this difference having no practical impact. In particular, from a mechanical performance outlook, soak and flash calcined clay mortars delivered similar compressive strength. While this research compares calcination methods, all tests were conducted in laboratory-scale electrically heated equipment; as such, it does not address heat-transfer limitations present in industrial calciners, thus requiring follow-up studies on industrial-scale reactors. • Soak and flash calcination of natural clays at different temperatures. • Comparing soak and flash calcined clays at similar dehydroxylation and particle size. • Flash calcination led to lower surface area of calcined clays compared to soak. • Minimal influence of the calcination method on hydration, rheology, and strength.