On fatigue and recovery of road asphalt mixtures

Abstract

This thesis, consisting of 7 peer-reviewed international journal publications is devoted to the investigation of fatigue and recovery properties of asphalt materials. Concerning the cracking mechanisms, the effects of both cracking in asphalt mixture and cracking at layers’ interface were considered. Since several test types are available for determination of asphalt mixture fatigue resistance, there is no consensus between researchers about the appropriate fatigue test. Considering the stress controlled test mode, it was found that uniaxial tension-compression test is the most reliable for evaluation of the asphalt mixture fatigue resistance. Furthermore, a new fatigue procedure was introduced, able to overcome the shortcomings if only a single test temperature is considered for the fatigue evaluation process (cp. EN 12697-24). This procedure allows a plausible evaluation of the asphalt mixture fatigue performance considering wide temperature range, with a marginally increased laboratory effort. Recovery potential of asphalt mixtures was addressed based on the concept of dissipated energy. The influence of several internal and external factors (bitumen polymer modification, ageing condition, binder content, degree of compaction and rest period duration) on recovery properties of asphalt mixtures was investigated. In order to overcome large scattering of the experimental results and consequently an erroneous evaluation of asphalt mixture recovery potential, a new recovery index was introduced. Moreover, the recovery potential of a specific asphalt mixture was investigated in detail, taking into consideration biasing effects such as nonlinearity and self-heating, observed during cyclic loading. Considering various asphalt mixtures and tack coats, the influence of test temperature and compressive normal stress on layers’ interface fatigue behaviour was determined. Based on this preliminary work, optimal test parameters were proposed, allowing a successful fatigue evaluation of the layers’ interfaces. Additionally, the comparison between results from the proposed cyclic shear fatigue procedure and results from monotonic shear test was performed. It was found that the resulting shear strength from monotonic shear test can be used only as a rough indicator for long term interface bonding performance, because not all research and field experience could be reflected in the test results.