Efflorescence: a critical challenge for geopolymer applications?

Zhang, Zuhua and Wang, Hao and Provis, John L. and Reid, Andrew (2013) Efflorescence: a critical challenge for geopolymer applications? In: Concrete Institute of Australia's Biennial National Conference (Concrete 2013): Understanding Concrete, 16-18 Oct 2013, Gold Coast, Australia.

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Abstract

Efflorescence is the formation of white salt deposits on or near the surface of concrete. For ordinary Portland cement (OPC) concrete, efflorescence is generally harmless except for the discolouration, and is best described as being 'a skin trouble and not a deep-seated disease'. However, for geopolymers, as they contain much higher soluble alkali content than conventional cement, efflorescence can be a significant issue when the products are exposed to humid air or in contact with water. In this study, the efflorescence phenomenon of geopolymers that synthesised using different activators, solid materials and curing conditions is observed. The efflorescence product is mainly sodium carbonate heptahydrate (Na2CO3·7H2O). The efflorescence potential has been compared via measurements of cation concentrations by atomic absorption spectroscopy (AAS), and determination of pH and electrical conductivity of geopolymer leaching solutions. At the same alkali content (in terms of Na2O), geopolymers synthesised at high temperature (80°C×28 d) exhibit less efflorescence rate than those synthesised at low temperature (20°C×28 d). NaOH activated geopolymers possess slower efflorescence than the sodium silicate solution activated specimens. Adding 20% slag can effectively reduce the initial efflorescence of a fly ash geopolymer. From a long term view, however, the efflorescence potential of such samples could be equivalent to the activated 100% fly ash when considering the alkali leaching results. Further investigations to prevent efflorescence, or at least to reduce its rate, are urgently required for wider applications of fly ash-based geopolymers.


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Item Type: Conference or Workshop Item (Commonwealth Reporting Category E) (Paper)
Refereed: Yes
Item Status: Live Archive
Additional Information: (c) 2013 The Author(s) The Author assigns to the Concrete Institute of Australia the copyright to the Contribution named above whereby the Institute shall have the right to publish the said Contribution in the Concrete2013 Conference Proceedings. 2. The Author retains the right to republish the Contribution without a request for permission from the Concrete Institute of Australia.
Faculty / Department / School: Current - Faculty of Health, Engineering and Sciences - School of Mechanical and Electrical Engineering
Date Deposited: 04 May 2014 06:13
Last Modified: 15 Dec 2014 04:27
Uncontrolled Keywords: geopolymer; efflorescence; fly ash; leaching; carbonation
Fields of Research : 03 Chemical Sciences > 0303 Macromolecular and Materials Chemistry > 030304 Physical Chemistry of Materials
09 Engineering > 0905 Civil Engineering > 090503 Construction Materials
09 Engineering > 0912 Materials Engineering > 091201 Ceramics
Socio-Economic Objective: B Economic Development > 86 Manufacturing > 8610 Ceramics, Glass and Industrial Mineral Products > 861001 Cement and Concrete Materials
URI: http://eprints.usq.edu.au/id/eprint/24943

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