Incorporating Impact of Binder Aging on Cracking Performance of Asphalt Mixtures during Design

Cracking – both environmental and load related - is a primary concern for asphalt pavements in New Hampshire. Cracking affects ride quality and allows water to penetrate from the surface to underlying soil layers, decreasing the life of the pavement and requiring more frequent maintenance or rehabilitation. It has been well recognized in the literature and through field observations that a mixture’s resistance to cracking decreases with time as the mixture ages in the field. The inclusion of already aged material in the form of reclaimed asphalt pavement (RAP) would also be expected to decrease the cracking resistance. Not all mixtures age at the same rate or to the same extent, and therefore, different mixtures could have very similar cracking properties soon after construction but may have drastically different properties after some level of aging. Therefore, it is important to have an understanding of how the cracking resistance of a mixture will change over time at the time materials are selected and mix designs are performed. Presently, the New Hampshire Department of Transportation (NHDOT) relies upon the performance grading of the binder to ensure the appropriate selection of materials to resist cracking in the field. However, recent research presented at various conferences and the Federal Highway Administration (FHWA) Expert Task Group meetings has shown that the current PAV aging for binders may only represent the condition of in service pavements after 2-3 years. In some cases, this is not adequate to differentiate or screen materials that may age quickly and lead to increased cracking. Also, research has shown the importance of evaluating the mixture properties, to include the effect of aggregate structure and minerology, on cracking performance; this is currently not part of the NHDOT specification.