INVESTIGATION ON THE EFFECT OF SLAG AND LIMESTONE POWDER ADDITION IN ALKALI ACTIVATED METAKAOLIN

Abstract

Alkali activated material has recently attracted gr eat attention as an environmentally friendly buildi ng material. Generally, it exhibits higher mechanical properties and better du rability when compared with Portland cement based m aterials. In this article, mixed alkali activated systems consisting of N-A-S- H and C-A-S-H hydrated gels were produced, using me takaolin as a dominated starting material and granulated blast furnace slag as an additional calcium and silicate source. Lime stone powder was then added into the blended metakaolin-slag system as a filler . The influences of slag and limestone powder on se tting times, strength development and microstructure were analyzed. The r esults indicate that, with the increasing slag cont ent, the setting time decreases; the compressive strength firstly increas es and then decreases after the slag replacement ex ceeds a critical value. Additionally, an optimum content for limestone powd er in the metakaolin-slag blends is around 15%. The FTIR spectra and XRD pattern present the changes in reaction products wh en slag was added, and the scanning electron micros cope results showed a denser matrix of the geopolymeric system when compa red to reference sample. However, no significant ch anges of reaction products were detected when limestone powder was in corporated, which indicates that the limestone powd er only works as a nonreactive phase in the alkali activated system.