Quantitative XRD study of amorphous phase in alkali activated low calcium siliceous fly ash

• XRD-based amorphous phase quantification in an alkali activated fly system developed.
• Amorphous phase quantification based on direct decomposition of the XRD signature in the reacting system into component pseudo-Voigt peaks.
• Peak characteristics of the amorphous reaction products identified with aluminosilicate gel are constant for the different curing temperatures and alkaline solutions.
• Calibration constants or the intensity profile of the component to estimate the amorphous content not required.
• Decomposition of XRD signature and can be applied directly to the activated fly ash system.

A technique based on direct decomposition of the XRD signature of the amorphous phase in alkali activated siliceous fly ash for determining the unreacted glassy phase content in fly ash and the amorphous reaction product content is presented. For the purpose of evaluation, a low-calcium siliceous fly ash, alkaline working solutions with different oxide ratios and two different curing temperatures were used. The intensity profile for the amorphous phase obtained from a Pawley intensity refinement of the XRD signature is expressed using pseudo-Voigt peaks for the individual intensity profiles of the glassy phase of fly ash and the amorphous reaction products. The peak characteristics of the amorphous reaction products identified with the aluminosilicate gel are found to be constant for the different curing temperatures and alkaline solutions. The percentage of reaction product and unreacted glassy content in fly ash were determined using selective dissolution combined with Rietveld refinement. The reaction product content and unreacted glassy phase content of fly ash determined from the decomposition of the XRD signature compare favourably with values obtained from selective acid dissolution. The amorphous products of reaction identified from the XRD analysis are shown to correlate well with the compressive strength. XRD is shown to be a powerful technique which can be used to study the influence of process variables on changes in the glassy phase content of fly ash and the evolution of products of reaction in alkali activated siliceous fly ash.