Effective control of flexible asphalt pavement cracking through quality assurance testing of extracted and recovered binders

Abstract

A total of 54 asphalt binders were obtained from six different Canadian (four municipalities) and United States (two State Departments of Transportation (DOTs)) user agencies. Regular AASHTO M 320 grades, critical crack tip opening displacements (CTOD), extended bending beam rheometer (EBBR) limiting low temperature grades (LLTG), and limiting phase angles grades T(δ = 30°) and T(δ = 45°), were determined for tank-sampled and extracted and recovered materials.While nearly all binders sampled from storage tanks at asphalt plants pass regular contract quality assurance (QA) requirements with ease, enhanced test methods showed major variability for materials of ostensibly the same AASHTO M 320 grade. The CTOD provides a measure of strain tolerance in the ductile state around the freeze-thaw regime. It ranged from a low of 8.4 mm for a contract in a PG minus 28 zone—likely burdened by too much reclaimed asphalt pavement (RAP) and/or poor virgin binder quality—to a high of 48.4 mm for a contract in a PG minus 34 zone. The CTOD varied by as much as threefold within the same climatic zone. Tank samples graded consistently better according to the CTOD compared to recovered binders, at times in a major way.Grade losses due to cold conditioning in the extended BBR protocol, which provide a measure of durability, ranged from a negligible 0.9 °C to a very significant 9.1 °C after only 72 h of cold conditioning. The EBBR LLTG was found to be highly correlated with the T(δ = 30°) grade (R2 = 0.85), and somewhat less correlated with T(δ = 45°) (R2 = 0.74). The CTOD was found to be highly correlated with the T(δ = 45°) (R2 = 0.90), and somewhat less correlated with the T(δ = 30°) grade (R2 = 0.86). Hence, the two limiting phase angle temperatures may be used, in the future, in a more precise, accurate, and practical specification protocol for the control of cold temperature cracking.