Federal Highway Administration
James E. Alleman
Peter Taylorptaylor@iastate.edu email >
Director, CP Tech Center
About the research
Five portland cement concrete (PCC) and five asphalt concrete (AC) pavement locations at each of seven field testing sites in the central and eastern United States represented a range of aggregate types, pavement surface ages, and climates. Albedo, thermal properties, and pavement surface characteristics data were collected, and cores were obtained to measure thermal properties in the laboratory. Test tracks at Auburn University’s National Center for Asphalt Technology (NCAT) and Minnesota’s MnROAD facility were used to collect 24-hour measurements for thermal model validation.
The albedo data showed that different parameters influence albedo for AC and PCC pavements, albedo approaches a steady value over time, and the albedo trends for each site differ. The AC albedo model reasonably predicted albedo over time using pavement age and coarse aggregate color. However, the PCC albedo model did not predict field albedo using pavement age, coarse aggregate color, and surface texture; additional field study is needed. Climate-related factors, particularly winter maintenance activities, may also play a role in pavement albedo.
Pavement thermal modeling required an understanding of the surface and thermal properties, small incremental units of time and layer thicknesses, 10 to 20 days of simulation to achieve balance throughout the pavement and subgrade system, and continuous data over an extended period. The thermal model predicted pavement thermal response in warm, dry conditions but did not account for the influence of moisture and freezing conditions.
Asphalt and concrete thermal properties vary and may have up to a 15% influence on AASHTOWare Pavement ME Design results. Current highway sustainability rating systems have recognized the complexity of pavement albedo, and the current systems either only address qualitative cool pavement goals or have no coverage of albedo-related metrics or outcomes.