Field validation study of low-temperature performance grading tests for asphalt binders

Current performance-graded asphalt cement specification testing to predict low-temperature performance was examined for effectiveness and deficiencies. The ability of various binder properties to predict cracking in the field was assessed for 17 trial sections constructed in northern Ontario. The tests included the currently used bending beam rheometer and direct tension tests, as well as a more fundamental fracture mechanics-based method. The results indicated that the currently used grading procedure predicted the ranking for most sections within each site reasonably well but was poor at predicting the onset of cracking. The need for improvement was illustrated with two sections on Provincial Highway 631, which were constructed in 1991 with binders of the same grade but which showed a difference in transverse cracking severity of nearly a factor 20. Furthermore, two sections on Provincial Highway 118, constructed in 1994 with binders of almost identical grade, were cracked by a more modest difference of 40%. Finally, the PG 58-28 and both of the PG 58-34 sections, which were constructed in 1996 on TransCanada Highway 17 - and were exposed to minimum surface temperatures of -26.8°C in their first winter and -27.2°C in 2003 and hence should not have cracked - were damaged by a significant 169, 52, and 65 transverse cracks/km, respectively. Physical aging and notch sensitivity of the binders were indicated as major contributing factors for this early distress.