Effect of aggregate gradation and percentage of air voids on the fatigue behaviour of hot mix asphalts

Mechanistic empirical pavement design is based on modelling certain modes of failure for different pavement materials. In the Australian and New Zealand guidelines, the mechanistic pavement design is based on modelling fatigue and permanent deformation as the two major modes of failures. The Austroads guidelines and New Zealand supplement adopt the Shell fatigue performance function to model the fatigue behaviour of asphalt mixes. However, a wide range of asphalt mixes is used on New Zealand roads and they are all behave differently in their fatigue and permanent deformation performance. Therefore, the question here is whether one fatigue model can accurately fit the fatigue performance of all different asphalt mixes. This research examined the fatigue behaviour of two different types of asphalt mixes, namely AC10-80/100 and AC14-60/70. The AC10-80/100 is a dense graded hot mix asphalt with 10 mm maximum nominal size and made with 80/100 asphalt binder. The AC14-60/70 is dense graded hot mix asphalt with 14 mm maximum nominal size and made with an asphalt binder 60/70 penetration grade. The fatigue results of the finer gradation and softer binder (AC10-80/100) were considerably higher than the coarser and stiffer mix (AC14-60/70). Fatigue was measured using the fourpoints bending at constant strain spanning different strain levels. The fatigue models that govern the behaviour of these mixes were derived and the effect of air voids on the fatigue behaviour was investigated. New fatigue models were developed.