Both load and nonload-associated cracking of asphalt pavements are prevalent in Canada and the northern United States. It is essential to identify the rheological properties of the asphalt binder responsible for this type of distress. An asphalt durability research project began with the construction of six test pavements in Pennsylvania in September 1976 using AC-20 asphalt cements from different sources.

For seven years (1976 to 1984), periodical pavement performance evaluations were carried out, and climatological data were gathered. The rheological properties of original and aging asphalt binders were evaluated from periodic core samples.

The stiffness moduli of original and aged asphalt binders and asphaltic concrete were determined by two indirect methods (Heukelom and McLeod) at −23°C (−10°F) to evaluate low-temperature nonload-associated transverse cracking. Diametral creep measurements were made on pavement cores after seven years in service. Creep moduli were determined over a convenient range of loading times up to 1000 s and in the 4 to −20°C (39.2 to −20°F) temperature range. The creep data for each asphalt were reduced to a master curve using the superposition method so that the stiffness modulus of the viscoelastic asphaltic concrete can be obtained at a desired temperature and time of loading. Both indirect methods and direct measurements indicate that the stiffness modulus of the asphaltic concrete is a better indicator of the potential low temperature nonload-associated cracking.

Asphalt ductility values, determined at 15.6°C (60°F) after six years in service, seem to be consistent with the pavement performance. Higher ductility values are associated with lower incidence of load-associated longitudinal cracking.

Recommendations have been made to optimize the rheological properties of asphalt binders and asphaltic concrete to minimize the incidence of both load and nonload-associated cracking of asphalt pavements.