Thermo-Mechanical Characteristics of Blended White Cement Pastes Containing Ultrafine Nano Clays

Abstract

Abstract The aim of this work was to produce highly active and amorphous nano sized pozzolana by means of thermal activation of nanoclays and to utilize the thermally activated nanoclays as additives in white Portland cement pastes (WPC) to improve their thermo mechanical properties. The nanoclay used in this investigation is kaolin clay. The nano Kaolin was thermally treated at 750°C for 2 h to obtain active amorphous nano metakaolin (NMK). The effect of thermal activation on the dehydroxylation of the kaolin and the surface morphology of the resulting amorphous NMK were determined by using different techniques: X-ray diffraction spectroscopy (XRD), differential thermal analysis (DTA) and 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 flexure 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 flexure strength of cement products. There was an enhancement of compressive strength by about 50% and flexure 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 microstructure.