Update of the PG Binder Map in California Using the Enhanced Integrated Climate Model (EICM) and LTPPBind Online

Nine climate regions in California for mechanistic-empirical pavement design were identified in 2005 using data from weather stations in the National Climatic Data Center (NCDC) from 1961 to 1990, along with data from the Climatic Database for Integrated Model from 1976 to 1995. The climate data were analyzed using the Enhanced Integrated Climatic Model (EICM) software to predict pavement temperatures at different depths, including 28 different flexible pavement structures. For asphalt pavement, the most important environmental variable is temperature. The 2005 climate region map also included asphalt binder performance grades (PG) for each climate region, developed using EICM and Long-Term Pavement Performance (LTPPBind) (v.2.0), resulting in four different PG grades for the nine regions. The number of PG grades was reduced from a larger number identified by the PG binder grade specification criteria to simplify the number of grades that would need to be produced in the state. This study evaluated the current California asphalt binder performance grade map developed in 2005, reviewed representativelocations in each climate region, calculated updated estimates of pavement temperatures using two methods, and recommended updates to the current California PG binder map. Climate data from 1990 to 2019 are now available from two different sources: NCDC and the Modern-Era Retrospective Analysis for Research and Applications (MERRA) from satellite information. Pavement temperatures wereobtained at different depths, and several pavement structures were analyzed using LTPPBind Online and the latest version of EICM. This study also included a sensitivity analysis of different modeling parameters, such as base and subbase thicknesses, heat capacity, and thermal capacity of the pavement. For each of the nine climatic regions, a representative city was selected based on criteria to ensure that the weather in that city is typical of the entire climate region and that the weather dataset is complete. The representative location for the Inland Valley was changed from Sacramento to Fresno to better reflect the temperatures found in most of the valley, away from the marine influence that affects Sacramento temperatures. The high-temperature and low-temperature PG binder calculations from LTPPBind Online are quite a bit lower than those from EICM for four regions that generally have colder temperatures. The recommended high-temperature PG for the Inland Valley was suggested to be increased, resulting in a recommended PG 70-10 specification. These recommendations do not consider the effects of larger volumes of heavy trucks and/or where trucks are moving at slower speeds. It is recommended that the Caltrans approach of allowing designers to use a binder with a high-temperature PG that is one grade higher than the normally recommended binder be continued.