Characteristics of Asphalt Binders Foamed in the Laboratory to Produce Warm Mix Asphalt
Publication: Journal of Materials in Civil Engineering
Volume 26, Issue 11
Abstract
Foamed asphalt binders are increasingly being used to produce warm mix asphalt. This paper presents the findings from a study conducted to (1) identify a repeatable and accurate method to characterize the quality of asphalt binder foams, and (2) use this method to evaluate the influence of water content, binder type, and foaming device on the quality of foamed binders. Laser and ultrasonic distance-measuring tools were used in combination with digital imaging of the foamed surface to quantify and better understand the expansion and decay of foamed asphalt binders over time. Measurements obtained from these methods were used to evaluate the extent and stability of foams produced using three different asphalt binders at three water contents and two laboratory foaming devices. Rheological properties and moisture content of selected binder residues were also measured. Results indicate that both the laser- and ultrasonic-based methods were promising in terms of their ability to provide a repeatable and detailed history of the change in volume of the foamed asphalt binder as the foam collapses. It was also shown that water content and binder type have a significant influence on the maximum expansion ratio and rate of collapse of foams. Higher water contents were associated with higher expansion ratios but also faster rates of collapse. The two foaming devices used in this study produced foams with similar properties. Rheological tests conducted on foamed binder residues revealed that the foaming process slightly increased the high temperature continuous performance grade (PG) of the binder.
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Acknowledgments
This study was conducted as part of the National Cooperative Highway Research Program (NCHRP) Project 9-53 “Properties of Foamed Asphalt for Warm Mix Asphalt Applications.” The support of NCHRP is greatly appreciated.
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Information & Authors
Information
Published In
Journal of Materials in Civil Engineering
Volume 26 • Issue 11 • November 2014
Copyright
© 2014 American Society of Civil Engineers.
History
Received: May 17, 2013
Accepted: Nov 12, 2013
Published online: Nov 14, 2013
Discussion open until: Oct 30, 2014
Published in print: Nov 1, 2014
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