Forensic Investigation and Validation of Energy Ratio Concept

The energy ratio (ER) concept was recently introduced as an accurate predictor of top-down cracking performance in Florida. Initial evaluation of ER with field projects in Florida confirmed its ability to distinguish between cracked and uncracked sections. To evaluate and validate the ER concept further, the Florida Department of Transportation designed and constructed two test sections at the National Center for Asphalt Technology test track. The primary difference between the two sections was the binder used in the upper two lifts. The first section used PG 67-22 and the second section used PG 76-22, which resulted in an ER of about twice the size. The section with the lower ER value cracked first and more extensively, though both sections experienced top-down cracking. This study was intended not only to look at ER as the primary factor to differences in performance but also to evaluate forensically the sections by using in situ strain measurements, coring, and interface bond strength testing. The strain regimes and bond strengths were found to be approximately equal between the sections, a finding that further validated the ER as a good predictor of top-down cracking performance.