Quantification of the Extent of Reaction of Metakaolin-Based Geopolymers using X-Ray Diffraction, Scanning Electron Microscopy, and Energy-Dispersive Spectroscopy

Abstract

This study presents four independent methods to determine the fraction of metakaolin dissolution in geopolymers. Two quantitative X-ray diffraction (XRD) results agreed with two independent techniques using scanning electron microscopy. The fraction of the metakaolin consumed varied from 10(8) to 75(3) wt% for geopolymers with compressive strengths varying from 3.1(2) to 67(17) MPa, respectively. It is proposed that the increase in strength with higher consumption of metakaolin is primarily due to the resultant changes in the matrix chemistry rather than changes in the quantity of matrix. Input Si/Al ratios of 1.5, 1.9, 2.5, and 3.0 resulted in matrix Si/Al ratios of 1.7, 2.3, 3.8, and 21. As anticipated the fraction of metakaolin dissolved was found to vary with OH- concentration. The area ratio method and the partial or no known crystal structure method have been identified as suitable for analysis of geopolymerization by time resolved XRD.