Abstract
A concern with the disposal, use, and general management of coal fly ash (CFA) is the potential for leaching of trace elements. This study provides data and analysis for an innovative method to mitigate leachate generation through engineered water repellency. Engineering water repellency involves modifying the surface of CFA particles with organo-silane (OS). Results indicate that the extent of water repellency can be quantified more accurately with contact angle (CA) measurements determined by increasing a drop size until the three-phase contact line motion becomes approximately constant. For each sample a minimum drop size at which the three-phase contact line motion reaches a stable motion has been identified. This approach allows for CAs to be measured with an accuracy of degrees, as opposed to degrees or greater with conventional approaches. Five types of CFA were tested using three different OS chemicals at different mix ratios (weight based). This article reports on the pattern that each of the modified CFA exhibits as a function of treatment type and level as well as the unique relationship between steady state motion of the three-phase contact line and drop volume. The extent of water repellency varied considerably as a function of OS treated dosage, which ranged from 1:500 to 1:140 (OS:CFA, by weight). The CAs of all five unmodified CFAs were below 90 degrees whereas the modified CFA resulted in average values of 143°, 135°, 150°, 158°, and 140° for CFA-1, CFA-2, CFA-3, CFA-5, and CFA-6, respectively. This change in CA from hydrophilic () to hydrophobic () and superhydrophobic () clearly indicates the property of highly water repellent material (no infiltration), as a result leachate control is possible.
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Acknowledgments
The authors gratefully thank and acknowledge the financial support provided by the Environmental Research and Education Foundation (EREF).
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Information & Authors
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Published In
Journal of Materials in Civil Engineering
Volume 29 • Issue 9 • September 2017
Copyright
©2017 American Society of Civil Engineers.
History
Received: Jul 11, 2016
Accepted: Jan 19, 2017
Published ahead of print: Apr 14, 2017
Published online: Apr 15, 2017
Published in print: Sep 1, 2017
Discussion open until: Sep 15, 2017
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