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

Abstract

Alkali activated material has recently attracted great attention as an environmentally friendly building material. Generally, it exhibits higher mechanical properties and better durability when compared with Portland cement based materials. In this article, mixed alkali activated systems consisting of N-AS -H and C-AS -H hydrated gels were produced, using metakaolin as a dominated starting material and granulated blast furnace slag as an additional calcium and silicate source. Limestone powder was then added into the blended metakaolin-slag system as a filler. The influences of slag and limestone powder on setting times, strength development and microstructure were analyzed. The results indicate that, with the increasing slag content, the setting time decreases; the compressive strength firstly increases and then decreases after the slag replacement exceeds a critical value. Additionally, an optimum content for limestone powder in the metakaolin-slag blends is around 15%. The FTIR spectra and XRD pattern present the changes in reaction products when slag was added, and the scanning electron microscope results showed a denser matrix of the geopolymeric system when compared to reference sample. However, no significant changes of reaction products were detected when limestone powder was incorporated, which indicates that the limestone powder only works as a non-reactive phase in the alkali activated system.