New Test Method to Obtain pH Profiles due to Carbonation of Concretes Containing Supplementary Cementitious Materials
Publication: Journal of Materials in Civil Engineering
Volume 19, Issue 11
Abstract
The writers have carried out an investigation to develop apparent pH profiles of concretes for a variety of cement blends viz. normal portland cement containing by mass 30% pulverized fuel ash, 50% ground granulated blast-furnace slag, 10% metakaolin, and 10% microsilica, chosen to replicate common replacement levels, along with 100% normal portland cement (OPC) mix. The samples were exposed in an accelerated carbonation environment (5% ) for during which pH profiles were obtained every week as the concrete carbonated. Measurement of air permeability, carbonation depth, resistivity, and calcium hydroxide content were performed to assist in interpretation of the results. The nature of the pH profiles obtained depended on both the type of binder and the duration of exposure to the carbonation environment. Utilizing the pH profiles, a rate of carbonation was determined, which was found to depend on the type of binder. Both the rate of carbonation and the depth of carbonation after of exposure indicated that OPC concrete performed better than concretes containing supplementary cementitious materials. It was also determined that the gas permeability alone cannot provide an accurate indication of the likely rate of carbonation. The thermogravimetric analysis suggests the existence of a relationship between calcium hydroxide content and the apparent pH of carbonated concretes. On the basis of the results in this paper, it can be concluded that the pH profiles, using the technique described in this paper, can be used for measuring the carbonation resistance of concretes containing supplementary cementitious materials.
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Acknowledgments
This project was funded by the Engineering and Physical Science Research CouncilEPSRC-GB (EPSRC). This and the use of facilities provided by the School of Civil Engineering at Queen’s University of Belfast is gratefully acknowledged. The writers also gratefully acknowledge the invaluable guidance provided by Professor W. J. McCarter at Heriot-Watt University in resistance measurements using embedded electrodes.
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Information
Published In
Journal of Materials in Civil Engineering
Volume 19 • Issue 11 • November 2007
Pages: 936 - 946
Copyright
© 2007 ASCE.
History
Received: Jul 27, 2004
Accepted: May 15, 2007
Published online: Nov 1, 2007
Published in print: Nov 2007
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