Thermal Treatment and Pozzolanic Activity of Calcined Clay and Shale

Abstract

Clayminerals are the most abundant raw materials for calcined pozzolans. Thermaltransformation includes dehydration, dehy­droxylation, mineral collapse, andneo-formation. Depending on the type and amount of clay mineral, and the natureand amount of associated minerals, the thermal treatment determines the pozzo­lanicactivity. In this paper, 10 natural shales or clays (six illite, two kaolin,and two loess) from Buenos Aires Province (Argentina) were identified using X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FTIR), andthermogravimetry (TG). The thermal transformation was checked by XRD or FTIR and the elec­trical conductivity (EC) at the calcination window. The pozzolanicactivity was evaluated using the Frattini test and strength activity index (SAI). The Frattini test gives positive results after 7 days and SAI is greaterthan 0.90 at 28 days, but the compressive strength development depends on mainclay mineral. The EC was effec­tive to evaluate the Ca(OH)2 fixationduring the first time and it is related to the specific surface obtained.