The Influence of Binder Rheology on the Cracking of Asphalt Mixes in Airport and Highway Projects

It is well known that asphalt rheology affects the cracking performance of asphalt binders. For many years researchers have struggled to develop tests that adequately deal with this aspect of pavement performance in a manner that can be incorporated rapidly into a specification. The use of the fatigue parameter developed during the Strategic Highway Research Program (SHRP), G* sin delta, has been shown to be a poor surrogate for cracking performance. Other tests, such as the direct tension test, used for cold-temperature cracking, also have been implemented poorly into specifications. However, use of the bending beam rheometer as an indicator of cold-temperature cracking has been widely adopted. As a result, a pavement stiffness of 300 MPa has been regarded as a reasonable parameter for cold-temperature cracking performance. The interrelationship between cold-temperature cracking parameters and those selected for fatigue cracking is not well understood. The onset of brittle behavior that occurs around 300 MPa stiffness and the selection of a fatigue parameter G* sin delta at 5 MPa are not wildly divergent in concept. More recently, the Glover-Rowe parameter has been revealed as a good indicator of cracking performance. In this paper we explore those differences that have occurred and make suggestions for the use of alternate parameters to better define the rheology of the binder as it relates to cracking.