Fatigue Characteristics of Bitumen-Filler Mastics and Asphalt Mixtures

Fatigue cracking is considered to be the primary failure mechanism that occurs at ambient temperatures in an asphalt pavement. The bituminous binder plays an important role in this failure mechanism, because fatigue cracking tends to take place predominately within the binder itself. Oscillatory tests using a dynamic shear rheometer (DSR) and wheel tracking fatigue tests were carried out on a wide range of bitumen-filler mastics and on asphalt mixtures containing the corresponding mastics to investigate their fatigue relationships. The addition of the mineral filler to bitumen was found to have a significant influence on the fatigue life of mastic owing to the stiffening effect and the filler particles interrupting the crack growth in the mastic. The results of stiffening ratio showed that the 65% mastics were in the concentrated suspension region, whereas the 35% mastics were in the dilute suspension region. In terms of shear stress, the fatigue order was 40/60 pen bitumen followed by 35% mastic, with 65% mastic having the highest fatigue performance. In terms of shear strain, the fatigue order was the reverse of the fatigue relationships versus stress, but the 40/60 pen bitumen had the greatest slope compared with the bitumen-filler mastics. No loading mode dependency occurred with results undertaken on the dilute suspension mastics, whereas testing mode had an influence on fatigue life for the mastics with concentrated suspension. In addition, the fatigue performance of asphalt mixtures seemed to be more sensitive to the wheel load rather than the concentration and nature of bitumen-filler mastics. The slope of the fatigue line for the mixtures was synonymous with that of the fatigue line for the mastics with concentrated suspension when subjected to wheel tracking testing rather than DSR oscillatory shear testing. DOI: 10.1061/(ASCE)MT.1943-5533.0000450. (C) 2012 American Society of Civil Engineers.