A major emerging application of calcined clays is in cementitious materials, including as a substitute for Portland cement and as a precursor for alkali-activated cements . Much investigation has gone into understanding the links between clay mineralogy, calcination conditions, and the chemical reactivity of calcined clays in cementitious systems, a process that is somewhat complicated by the variety in mineralogy of clay-based resources (Alujas . There is debate regarding the exact role and influence that Al coordination has on a calcined clay's chemical reactivity. The fraction of 5-fold co-ordination Al has been proposed as an indicator of reactivity for meta-kaolinite , while subsequent studies argue against this .