Modeling of fatigue damage functions for hot mix asphalt and application to surface cracking

This paper presents a unique approach to analyzing surface cracking in HMA pavements, based upon the concept of reduced cycles. In the first half of the paper, empirical equations are presented for predicting damage curves for any HMA mixture under a wide range of loading conditions. These equations have been developed using a large database of fatigue test results, and confirmed with data from several independently gathered data sets. The equations use as predictors modulus and other parameters calculated from the change in modulus with time and/or temperature. The second half of the paper applies these equations to fatigue experiments carried out at the Federal Highway Administrations Automated Loading Facility (ALF) in MacLean, VA. This analysis involved estimating the reduced cycles at critical points in the surface of the test sections at the initial appearance of surface cracking. Statistical methods were then used to develop equations for predicting the onset of cracking. Although the approach is promising, some additional work is needed before the method should be applied to general problems in pavement design and analysis.