Carbonation and pH in Mortars Manufactured with Supplementary Cementitious Materials
Publication: Journal of Materials in Civil Engineering
Volume 21, Issue 5
Abstract
An investigation of carbonation in mortars and methods of measuring the degree of carbonation and pH change is presented. The mortars were manufactured using ordinary portland cement, pulverized fuel ash, ground granulated blast-furnace slag, metakaolin, and microsilica. The mortars were exposed to a carbon dioxide-rich environment (5% ) to accelerate carbonation. The resulting carbonation was measured using phenolphthalein indicator and thermogravimetric analysis. The pH of the pore fluid and a powdered sample, extracted from the mortar, was measured to give an accurate indication of the actual pH of the concrete. The pH of the extracted powder mortar sample was found to be similar to the pH of the pore fluid expressed from the mortars. The thermogravimetric analysis suggested two distinct regions of transport of within mortar, a surface region where convection was prevalent and a deeper region where diffusion was dominant. The use of microsilica has been shown to decrease the rate of carbonation, while pulverized fuel ash and ground granulated blast-furnace slag have a detrimental effect on carbonation. Metakaolin has little effect on carbonation.
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© 2009 ASCE.
History
Received: Jan 23, 2008
Accepted: Nov 5, 2008
Published online: May 1, 2009
Published in print: May 2009
Notes
Note. Associate Editor: Byung Hwan Oh
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