Detailing an Improved Heat Transfer Model for Pavements

Abstract

Temperature profiles are a fundamental input into mechanistic-empirical pavement analysis and design, and the enhanced integrated climatic model (EICM) is the state-of-the-practice for calculating those profiles. The EICM has also been used in other applications, such as analysis to evaluate the effects of climate change on pavements and to estimate the effects of pavements on urban heat islands. The calculations in the EICM for pavement temperatures can be viewed as having two primary components that together act as a system: the thermal model describing conductance of temperatures throughout the pavement, and the boundary conditions that include the convective terms at the pavement surface, an energy balance model to predict the solar radiation at the surface of the pavement and a specified lower boundary condition (generally constant temperature at defined depth). As is shown in this paper, the current EICM models overpredict temperatures during hot times and in no-wind conditions, while also underpredicting (albeit to a lesser magnitude) during cold conditions. This result implies that the increases in pavement temperatures predicted to occur with climate change are likewise overestimated. Conversely, because the convection coefficient is incorrect, the predicted amount of energy contributing to urban heat islands will also not be correctly predicted using the current EICM models. Although improvements to the solar model are noted, this paper focuses on improvements to the thermal model and convective boundary condition using modern heat transfer principles and data from the Long-Term Pavement Performance database.