Incorporation of Environmental Effects in Pavement Design

Environmental conditions have a significant effect on the performance of both flexible and rigid pavements. External factors such as precipitation, temperature, freeze-thaw cycles, and depth to water table play a key role in defining the bounds of the impact the environment can have on the pavement performance. As part of the new US Mechanistic-Empirical Pavement Design Guide (MEPDG) being developed under the overall project sponsored by the National Cooperative Highway Research Program (NCHRP project 1–37A), a climatic modelling tool called the Enhanced Integrated Climatic Model (EICM) was implemented to incorporate the changes in temperature and moisture of unbound materials into the design process. Currently a new independent review project (NCHRP 1–40) is reviewing this model to correct errors and to develop further enhancements to produce a final methodology ready for approval/disapproval vote by AASHTO in 2006. This paper reflects the methodology used for the MEPDG and present the models incorporated by Arizona State University into the EICM, the input needed and the outputs generated by the program. A discussion on how EICM determines the temperature and moisture distribution within the pavement system is also presented.