Albedo as an engineering property of concrete pavements

Abstract

Albedo or solar reflectance is a thermal property of concrete pavements that is used in pavement design as well as life cycle assessment. In either application, it has a major impact on distress predictions and the urban heat island quantification, respectively. Hence, understanding the factors that affect the albedo of concrete pavement is important. The spectral reflectance of three types of concrete, one made of white cement and no supplementary materials, one with white cement and 15% fly ash, and one with gray cement and 15% fly ash, were determined using a spectrophotometer. Using the SMARTS 2.95 model, the solar spectrum adjusted for pavements in two locations, San Antonio (Texas) and Singapore, were determined at an altitude of 200 m and 3,000 m for representative days and hours in the year 2000. The albedo was determined as a solar spectrum-weighted average of the solar reflectance and compared to that determined with the current ASTM G173 standard. The most important variable affecting concrete albedo was found to be the mix design, followed by the time and geographical location of measurement. While the maximum error as compared to the current standard was small, the error with respect to the value used in practice was very large, indicating the need to measure albedo to avoid overly conservative albedo inputs into pavement design and LCA.