Thermal stability and pozzolanic activity of calcined illite

Standard illite (American Clay Society, IMt-1) was calcined at 650,790 and 930°C for 100 minutes. Both the raw and calcined samples, before and after being mixed with Ca(OH)2 in the presence of simulated cement pore solution, were studied by DTA, TG (for raw illite), XRD, SEM, EMPA and chemical solubility. The reaction rate of the mixtures was monitored by a chemical shrinkage test. Technological properties of the untreated and calcined illite-cement mortars were studied by theology (flow) and by a compressive strength test after reaction for 2, 7, 28 and 91 days. The current investigation revealed that illite has low pozzolanic activity. Dehydroxylation at 650°C does not upgrade it significantly. Further calcination at 790°C brings about considerable activation but it still does not qualify as a pozzolan. Calcination at 930°C produces the highest pozzolanic activity. Compressive strength of the mortar with 930°C illite is 79% of that of reference ordinary portland cement.