Structural characistics of borax-metakaolin and borax-fly ASH based geopolymer systems

Abstract

The main focus of this study is to investigate the effect of inclusion of borax on structural properties of metakaolin and C type fly ash based geopolymers. Various structural characterization techniques including Fourier Transform Infrared Spectroscopy (FTIR), X-Ray Diffraction (XRD), Scanning Electron Microscopy (SEM) and Thermogravimetric Analysis (TGA) are performed to analyze a set of borax containing metakaolin and fly ash-based geopolymers with molar B/Si ratios between 0 and 1. Compressive strength tests are also carried out to understand the effect of boron inclusion mechanical strength values. In the first part of thesis, borax-metakaolin based geopolymer samples are investigated. Geopolymers have amorphous character together with quartz and boron-including crystalline components in borax- metakaolin based geopolymer systems. The intensity of the FTIR bands in this system increases systematically with B/Si ratio. This situation is also consistent with observation of needle and star like crystalline structures in the SEM measurements. The geopolymer with B/Si ratio of 1 has a peak at 620 cm-1 which is assigned to polyborosiloxane bridges, showing incorporation of boron atoms into the silica network. The second part of this thesis includes comparison of structural characteristics borax- metakaolin and borax-fly ash based geopolymers with different B/Si ratios. The FTIR results of geopolymers exhibit borosiloxane bridge as a small peak at 685 cm-1 and shoulder at 875 cm-1. Borosilicate structural units are also seen at 630 cm–1 in the Raman spectrum of borax-fly ash based geopolymers supporting the FTIR results. The presence of new structural units related to boron addition are observed same as the SEM images as the star and needle like structures. Boron content seems to have positive effect in compressive strength.