A simple testing method to evaluate fatigue fracture and damage performance of asphalt mixtures

This paper describes the development and validation of a simple and reasonable fatigue testing apparatus and analysis method that may be able to either supplement or replace traditional fatigue testing and analysis. In this method, three mechanical tests with cyclic torsional loading are performed to characterize basic linear viscoelastic material properties and the fatigue behavior of the asphalt matrix, which is, in this case, defined as a composite of asphalt mastic (binder and mineral filler) and the fine aggregate fraction. The testing induced damage in asphalt matrix that was sensitive to the materials tested. Damage accumulation within each asphalt mixture tested was due to microcrack development and propagation and ultimately to fatigue failure as a result of fatigue crack damage. This damage was monitored using image analysis. Testing results from asphalt matrix mixtures generally agreed well with testing data on asphalt binders and with fatigue testing results from asphalt concrete mixtures. Furthermore, the mechanically-developed fatigue life prediction model can be applied to various asphalt mixture systems by simply performing fundamental material property tests such as frequency sweep tests. Successful development of this testing protocol has the potential to become a specification-type test method because it is fast, repeatable, and accurate.