Effects of metakaolin on nanomechanical properties of cement paste

Abstract

Metakaolin (MK) is a pozzolanic material, which is a dehydroxylated form of the clay mineral kaolinite. It is obtained by calcination of kaolinite clay at a temperature between 500 °C and 800 °C. In cement matrix, MK reacts with Ca (OH)<inf>2</inf>, to produce calcium silicate hydrate (CSH) gel. MK also contains alumina that reacts with Ca(OH)<inf>2</inf> to produce additional alumina-containing phases, including C<inf>4</inf>AH1<inf>3</inf>, C<inf>2</inf>ASH<inf>8</inf> and C<inf>3</inf>AH<inf>6</inf>. This research aims to provide a better understanding of the effects of MK on the nanomechanical properties of the main phases present within the cement paste. Two different mixes were prepared, one control mix and the other one with 10% MK (by cement weight). A constant waterbinder ratio of 0.4 was used for both the mixes. Fraction volumes determined from nanoindentation testing show an increase in the amounts of high-density CSH at the cost of low-density CSH gel in cement pastes containing 10% MK.