Advanced Laboratory Performance Testing Towards Asphalt Mix Performance Grading (Mix-PG)

The introduction of high amounts of recycled materials and chemical additives into asphalt mixes indicates that relying solely on asphalt binder Performance Grading (PG) is not sufficient to predict asphalt mixes performance in the field. Therefore, this research developed an asphalt mix PG system to assess five plant-produced Superpave (SP) 12.5 surface course asphalt mixes. The Disc-Shaped Compact Tension (DC(T)), Hamburg Wheel Tracking (HWT) tests, and the Illinois Flexibility Index Test (I-FIT) were employed. The DC(T) tests were conducted to characterize the low-temperature cracking resistance of asphalt mixes. Subsequently, the mix continuous low-temperature PGs was determined, where a suggested minimum threshold value of DC(T) fracture energy was met. To evaluate the rutting resistance of asphalt mixes, the HWT tests were performed. Afterward, the mix continuous high-temperature PGs were determined, where a suggested maximum threshold value of creep slope obtained from the HWT test was fulfilled. The I-FIT tests were conducted to characterize the intermediate-temperature cracking resistance of asphalt mixes and verify whether asphalt mixes satisfied a suggested minimum threshold value of Flexibility Index (FI) at their corresponding mix continuous intermediate temperature PGs. This research revealed that meeting a minimum or a maximum threshold value of a specific laboratory test, at a particular temperature, may not result in a comprehensive evaluation of mix performance. However, utilizing a space diagram of mix PG, which integrates the mix’s continuous low- and high-temperature PG, and FI value, has the potential to select suitable asphalt mixes based on their expected performance for a specific climate.