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Open AccessArticle

The First 20 Hours of Geopolymerization: An in Situ WAXS Study of Flyash-Based Geopolymers

John de Laeter Centre, Curtin University of Technology, GPO Box U1987, Perth WA 6845, Australia
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Academic Editor: Claudio Ferone
Materials 2016, 9(7), 552; https://doi.org/10.3390/ma9070552
Received: 15 May 2016 / Revised: 29 June 2016 / Accepted: 4 July 2016 / Published: 8 July 2016
(This article belongs to the Special Issue Advances in Geopolymers and Alkali-Activated Materials)
This study followed the first 20 h of flyash geopolymerization at 70 °C using time resolved Wide Angle X-ray Scattering (WAXS). The extent of dissolution of the amorphous phase of the flyash was determined to range from 29% to 54% for the different formulations trialed. The dissolution rate of the flyash significantly reduced after the first 5 h for all samples. During the formation stage of the geopolymer there were significant temporal variations in the chemistry of the dissolved solution due to the rate of flyash dissolution, with a relative standard deviation of 20%, 57% and 24% for the Si/Al, Na/Al and H/Si ratios, respectively. Utilizing the Power Law, scattering in the low angle region of the WAXS pattern combined with the geopolymer peak area yielded a measure which correlated with the compressive strength—providing a new method to measure the flyash dissolution and geopolymer formation processes independently. The evolution of several zeolite-like phases was followed, noting there are different formation mechanisms involved even within the same sample. Four samples were examined with compressive strengths ranging from 14(2)–50(9) MPa, each was synthesized with flyash from Collie Power Station (Western Australia) activated with sodium silicate solution of varying concentrations. View Full-Text
Keywords: geopolymers; flyash; dissolution; XRD; time-resolved; amorphous geopolymers; flyash; dissolution; XRD; time-resolved; amorphous
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Williams, R.P.; Van Riessen, A. The First 20 Hours of Geopolymerization: An in Situ WAXS Study of Flyash-Based Geopolymers. Materials 2016, 9, 552.

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