Assessment of pozzolanic activity of thermally activated clay and its impact on strength development in cement mortar

Abstract

Natural kaolinitic clay from Khyber Pakhtoonkhwa, Pakistan was thermally activated at different temperatures and its pozzolanic behavior was studied. Thermal activation was carried out in an electrical muffle furnace at 200, 400, 600 and 800 °C for two hours. The index of order/disorder and structural changes with thermal treatment were studied using X-ray diffraction (XRD) and Fourier transformed infra-red spectrometry (FTIR). The pozzolanic behavior of all the samples was evaluated using an electrical conductivity test, lime consumption (LC) test and strength activity index (SAI). This study confirmed that natural kaolinitic clay other than pure kaolinite can act as an interesting pozzolana when thermally activated. The best temperature for thermal treatment of natural kaolinitic clay is 800 °C, while the permissible replacement in mortar is 25% as confirmed from the compressive strength measurement.