Physico-mechanical characteristics of blended white cement pastes containing thermally activated ultrafine nano clays

Abstract The aim of this work is to produce highly active and amorphous nano sized pozzolana by means of thermal activation of nano clays and to utilize the thermally activated nano clays as additives in white Portland cement pastes (WPC) to improve their thermo mechanical properties. Nano-kaolin was thermally treated at 750 °C for 2 h to get active activated nano-metakaolin (NMK). The effect of thermal activation on the dehydroxylation of the nano-kaolin was determined by using different techniques such as; X-ray diffraction spectroscopy (XRD) and differential thermal analysis (DTA). The surface morphologies of both nano-kaolin and NMK were studied by transmission electron microscopy (TEM). NMK were incorporated at a rate of 2%, 4%, 6%, 8%, 10%, 12% and 14% by weight of cement. Hardened blended cement pastes were prepared by using water/cement ratio (W/C) of 0.3 by weight and hydrated for various curing ages 3, 7 and 28 days. In order to study the mechanical and physical characteristics of the hardened cement pastes incorporating NMK, different techniques were used such as compressive and flexural strength testing, differential scanning calorimeter (DSC), X-ray diffraction (XRD) and scanning electron microscope (SEM). The experimental results of this study showed that thermal activation of the nano kaolin leads to transformation of the kaolinite to amorphous phase accompanied with the reduction in grain size. The partial replacement of cement by NMK is helpful in enhancing the compressive and flexural strength of cement products. There was an enhancement of compressive strength by about 50% and flexural strength by 36% at 10% nanoclay. The microstructure of the cement blended with NMK was denser, compact and more uniform than that of the conventional cement.