Facile production of nano-scale metakaolin: An investigation into its effect on compressive strength, pore structure and microstructural characteristics of mortar

Abstract

The use of nano materials as partial replacement for cement has been considered all over the world, particularly in the production of high strength and high performance cement based structures. This study aims at facile production of nano-scale metakaolin (NMK) and investigating its influence on the mechanical, pore structure, phase composition and microstructure characteristics of hardened mortar. NMK with superior surface area was effortlessly prepared via exfoliation of thermally activated ordinary kaolin (MK) with the aid of organic ammonium chloride. SEM micrographs confirm the formation of nanoplates of few nanometers in thickness; furthermore, specific surface area was evaluated by the BET analysis. The exfoliated NMK showed greatly enhanced surface area. Two groups of MK-blended mortars were prepared in which cement was partially replaced with 0, 1, 2, 3, 4, and 5 wt% of MK and Exfoliated NMK. Exfoliated NMK was found to be highly effective in enhancing the compressive strength of mortar and an optimum replacement within 3% can be concluded. There were enhancements by about 24% compared with the unexfoliated MK blended mortar and 54% compared with the plain ordinary mortar. The BET analysis confirmed that; NMK provides significant refinement in pore structure of blended mortar. The phase composition analysis by TGA and SEM indicate that NMK acts not only as a filler to improve the packing inside the cementitious matrix, but also as an activator to promote hydration and pozzolanic reactions.