Review of Current Asphalt Cement Performance Grade Temperature Requirements in the Maritime Provinces

Performance graded asphalt binders are selected under the Superpave system to provide superior performance according to the climate in which the pavement will serve.  Rutting and fatigue resistance are provided at selected reliability levels by meeting various physical properties at corresponding site-specific high and low design pavement temperatures.  These design temperatures have been previously determined using climatic data from across North America within the LTPPBind software version 3.1, and more recently can be assessed using LTPPBind Online.  The high and low design pavement temperature and performance grades were determined using the LTPPBind software, and by using the LTTPBind version 3.1 models with climate data captured through the Road Weather Information Systems (RWIS) network utilized by the Maritime Provinces.  Difference in the results were compared to assess possible changes arising from climate change effects and to update pavement temperatures required for binder testing under AASHTO M332 specifications.  LTTPBind Online was discontinued in the study due to differences observed in computing certain climate statistics compared to version 3.1, an error detected in the high temperature grade results at 98% reliability, and unrealistic results that were observed for various locations.  An average increase in the calculated high temperature grade requirement of 2.89 ˚C was observed between results based on current and local RWIS data versus 20-year Environment Canada climate data used within LTPPBind 3.1.  This change occurred over approximately 17 years, indicating that a 6 ˚C change corresponding to a full performance grade may be expected for the high temperature grade over 35 years, assuming the current rate of change remains constant.   A slower average rate of change in the low temperature grade shift was observed at 2.11 ˚C over 17 years, corresponding to 48 years of longevity for a full 6 ˚C performance grade interval.  Similar results were observed between the calculated design pavement temperatures obtained using the RWIS air and pavement temperature data.  This verifies the LTPPBind model and the observed changes in the design temperatures over time.  Design pavement temperatures should be evaluated annually using a shorter 10-year window of climate data to monitor the rate of change and predictions of future performance grade requirements.