Reflectance Spectra of Thermochromic Asphalt Binder: Characterization and Optical Mixing Model
Publication: Journal of Materials in Civil Engineering
Volume 28, Issue 2
Abstract
Asphalt pavement constructed with traditional asphalt binder, which features high solar absorbance, is characterized by high surface temperatures during summer. This causes undesirable performance degradation (i.e., due to accelerated rutting, bleeding, etc.) and environmental consequences (i.e., urban heat island effects and volatile gas emission). Thermochromic asphalt binder, which is asphalt binder mixed with thermochromic materials, has been developed by the authors to dynamically control the solar reflectance and modulate the surface temperature of asphalt pavement. The goal is to improve its long-term durability and environmental friendliness. Thermochromic materials are substances that can reversibly change their colors in response to temperature. The binary thermochromic asphalt binder mixture is produced by incorporating thermochromic powders into a conventional asphalt binder. Measurements of spectral reflectance of thermochromic powders indicate that thermochromic materials feature higher solar reflectance at higher temperatures. In this paper, the spectral reflectance of thermochromic powders as functions of wavelength and temperature are fitted with common types of optical mixing models based on experimental data. Optical measurements conducted on the thermochromic asphalt binder mixture show that they feature more solar reflectance than conventional asphalt binders; furthermore, reflectance increases with temperature. The spectral reflectance of thermochromic asphalt binder also increases as the powder content increases. The common types of optical mixing formulas, including those based on Maxwell, Mori-Tanaka, and effective medium theory (EMT), etc., are used to establish the relationship between spectral reflectance of thermochromic asphalt binder and powder content. These optical mixing formulas provide a convenient way to predict the reflectance spectra of thermochromic asphalt binder and will assist its multifunctional design and optimization.
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Acknowledgments
This study is supported by the Ohio Department of Transportation via the Ohio Partnered Research Exploration Program in partnership with the Ohio Flexible Pavement Association. Technical liaisons from ODOT include David Powers, Roger Green, Lloyd Welker, and Adam Au. The support and assistance from these organizations and individuals are highly appreciated.
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© 2015 American Society of Civil Engineers.
History
Received: Jul 21, 2014
Accepted: May 21, 2015
Published online: Aug 7, 2015
Discussion open until: Jan 7, 2016
Published in print: Feb 1, 2016
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