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Materials 2015, 8(6), 3053-3067; doi:10.3390/ma8063053

Use of Gypsum as a Preventive Measure for Strength Deterioration during Curing in Class F Fly Ash Geopolymer System

School of Urban and Environmental Engineering, Ulsan National Institute of Science and Technology (UNIST), Ulsan Metropolitan City 689-798, Korea
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Academic Editor: Klara Hernadi
Received: 8 April 2015 / Revised: 7 May 2015 / Accepted: 20 May 2015 / Published: 29 May 2015
(This article belongs to the Section Advanced Composites)
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Abstract

This study discusses strength deterioration during the curing process of fly ash geopolymer and the use of CaSO4·2H2O (gypsum) as a deterioration remedy when the ash was synthesized using a 10M NaOH and Na-silicate solution. The strength decline was mainly due to the widespread formation of nanometer-sized cracks that were related to excessive Na and Si concentrations at an early age. Use of 2 wt% CaSO4·2H2O resulted in the best measured strength by temporarily reducing Na and Si concentrations; Na was absorbed by SO42, up to 11% in the matrix within one day, and formed Na2SO4 (thenardite), which gradually dissolved over time, slowly releasing Na ions. However, more than 4% gypsum suppressed overall strength development because too many Na ions were locked into Na2SO4 and could not participate in geopolymerization. The addition of gypsum impeded glass dissolution and even halted the process when more than 4% gypsum was used. View Full-Text
Keywords: fly ash; geopolymer; gypsum; Na2SO4; strength deterioration; nanometer-crack fly ash; geopolymer; gypsum; Na2SO4; strength deterioration; nanometer-crack
This is an open access article distributed under the Creative Commons Attribution License which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. (CC BY 4.0).

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MDPI and ACS Style

Jun, Y.; Oh, J.E. Use of Gypsum as a Preventive Measure for Strength Deterioration during Curing in Class F Fly Ash Geopolymer System. Materials 2015, 8, 3053-3067.

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