September 29th, 2014No Comments, Preserve Infrastructure, by Guest Post.
Because winter maintenance is so costly, UDOT personnel asked researchers at Brigham Young University (BYU) to determine whether asphalt or concrete pavements require more winter maintenance. Differing thermal properties suggest that, for the same environmental conditions, asphalt and concrete pavements will have different temperature profiles. Climatological data from 22 environmental sensor stations (ESSs) near asphalt roads and nine ESSs near concrete roads were used to determine which pavement type has higher surface temperatures in winter.
Twelve continuous months of climatological data were acquired from the road weather information system operated by UDOT, and erroneous data were removed from the data set. In order to focus on the cold-weather pavement surface temperatures, a winter season was defined as the period from November through April, and the data were divided into time periods that were based on sunrise and sunset times to match the solar cycle.
To predict pavement surface temperature, a multiple linear regression was performed with input parameters of pavement type, time period, and air temperature. As shown in Table 1, the statistical analysis predicting pavement surface temperatures showed that, for near-freezing conditions, asphalt is better in the afternoon, and concrete is better for other times of the day. However, neither pavement type is better, on average, across the locations studied in this research. That is, asphalt and concrete are equally likely to collect snow or ice on their surfaces, and both pavements are expected to require equal amounts of winter maintenance, on average.
To supplement these analyses, which provided useful information about average pavement temperatures across the statewide pavement network, additional analyses of asphalt and concrete pavement surface temperatures were performed for a particular location in a mountainous region of northern Utah more typical of canyon areas. Asphalt and concrete pavement surface temperatures were directly compared at a location on U.S. Route 40 near Heber where asphalt and concrete meet end to end at the base of a mountain pass. As shown in Figure 1, an ESS was installed to facilitate monitoring of asphalt and concrete pavement surface temperatures, as well as selected climatic variables, at the site.
Data collected during the three winter seasons from 2009 to 2012 were analyzed in this research, and the same months and time periods used in the previous study were applied in this analysis as well. To compare the surface temperatures of the concrete and asphalt pavements during freezing conditions, multivariate regression analyses were performed. Equations were generated for three response variables, including the asphalt surface temperature, concrete surface temperature, and difference in temperatures between the asphalt and concrete surfaces.
The statistical models developed in the analyses show that the surface temperature of both asphalt and concrete pavement increases with increasing air temperature and decreases with increasing relative humidity and wind speed, and that the difference in pavement temperatures decreases with decreasing air temperature. For the studied site, the data indicate that concrete pavement will experience freezing before asphalt pavement for all time periods except late afternoon, when the pavement types are predicted to freeze at the same air temperature (see Table 2). Therefore, for material properties and environmental conditions similar to those evaluated at this U.S. 40 site, asphalt would require less winter maintenance, on average, than concrete.
Due to the interactions among albedo, specific heat, and thermal conductivity, the actual thermal behavior of a given pavement will depend on the material properties and environmental conditions specific to the site. As shown in this research, concrete pavement can be warmer than asphalt, which is typical of the statewide pavement network, on average, during late morning, evening, night, and early morning. However, the research also clearly shows that, in mountainous regions of northern Utah more typical of canyon areas, engineers may expect asphalt pavement to be warmer than concrete, or equal in temperature to it, during all time periods at sites that receive direct sun exposure, such as the one on U.S. Route 40 that was studied in this research. At such sites, selection of asphalt pavement may facilitate reduced winter maintenance costs; however, though statistically significant, relatively small differences in temperature between asphalt and concrete pavement surfaces may not warrant differences in actual winter maintenance practices. Other factors beyond pavement type, such as rutting and surface texture, may more strongly affect winter maintenance and should also be considered.
The results of the statewide comparison of wintertime temperatures of asphalt and concrete pavements, as well as the specific results for the U.S. 40 site near Heber, are detailed in two separate research reports available on the Research Division website.
This guest post was written by W. Spencer Guthrie, Ph.D., M.ASCE, Brigham Young University, and David Stevens, P.E., Research Program Manager, and was originally published in the Research Newsletter.