Effect of calcining temperature of kaolinite clay on the properties of Portland cement pastes containing metakaolin

Abstract

Metakaolin (MK) is a highly reactive pozzolan produced by calcination of kaolinite clay at high temperature. It has a high specific surface, which makes it very suitable as a cementing material in concrete. The utilization of calcined clay, in the form of MK, as a pozzolanic material for mortar and concrete has received considerable attention in recent years. This interest is part of the widely spread attention directed towards the utilization of wastes and industrial by-products in order to minimize Portland cement (PC) consumption, the manufacture of which being environmentally damaging. Another reason is that mortar and concrete, which contain pozzolanic materials, exhibit considerable enhancement in durability properties. In this investigation, the physico-chemical properties of artificial pozzolanic cement pastes containing MK produced by calcination of kaolinite clay at different temperatures (700, 800, 900, and 1000°C) were studied. PC was partially substituted for by 0,5,10,15 and 20 % ofMK by weight at different calcining temperatures. The characteristics of prepared mortars were investigated after curing in water for different periods (3,7,28 and 90 days) by determination of compressive strength and total porosity. The hydration kinetics was evaluated by determination of free lime contents. IR spectroscopic analysis was used to investigate the change in structure of mortars after curing. The change in morphology and microstructure of some hardened pastes were investigated by scanning electron microscopy (SEM) tests.