The effect of aging on feopolymers made from fly ash and matakolinite

Abstract

Geopolymers are formed by adding Si and Al generally in reactive glassy or fine grained phases to concentrated alkali solutions for dissolution and subsequent polymerisation to take place. We made geopolymers using fly ash or metakaolinite produced by heating kaolinite at 750°C for 15 h as Si and Al sources. Geopolymer pastes aged for between 1 day and 2 years after curing were investigated in this study. We characterised the materials by electron microscopy, x-ray diffraction analysis (XRD), differential thermal analysis/thermogravimetric analysis (DTA/TGA). BET surface area, infra-red spectroscopy and solid state nuclear magnetic resonance (NMR). Their density and porosity were determined by several methods Both types of geopolymers were predominantly amorphous and there were no changes in the minor crystalline phases with ageing as shown by XRD. The geopolymers made from fly ash showed significant differences in porosity and surface area with ageing. 27Al and 298i NMR indicated that the on-going reactions within the geopolymer matrix are contributing to these changes after the material has set and hardened. The DTA/TGA and density/porosity for the geopolymer made from metakaolinite did not show any significant changes. The differences between the two types of geopolymers will be discussed with respect to ageing.