Calcined illite-chlorite shale as supplementary cementing material: Thermal treatment, grinding, color and pozzolanic activity

Abstract

The thermal transformation (100–1100 °C) of two shales containing illite-chlorite (I/Ch), feldspars and quartz from La Cabañita quarry (Olavarria, Argentine) was studied by TG-DTA, XRD and FTIR. It included dehydration; dehydroxylation (350–800 °C) and the structural collapse of illite (950 °C); while the neoformations were hematite and iron spinel. For rotary kiln production, the glass formation due to feldspars melting at 1100 °C was the upper temperature limit. For the calcination temperature range of 900–1100 °C, grindability increased when calcination temperature increased, but the specific surface area decreased. The high Fe-content caused a reddish color of particle surface, but their cores were black. The pozzolanicity test was satisfied at 7 days and strength activity index was 0.84–0.97 and 0.94–1.04 at 28 and 90 days, respectively. The addition of calcined shale did not affect the mortar flow and the hydration products assembly. Calcined I/Ch shale was a slow reactive pozzolan with good strength at 90 days.