Evaluation of asphalt binder rutting parameters

Rutting in asphalt mixes is a common type of distress in pavements with thick asphalt layers. It is more severe for pavements subjected to high pavement temperatures, slow moving, uphill in mountainous areas and heavy traffic loads. A number of binder rutting parameters have been proposed by different researchers for ranking/grading of the binders in terms of their rutting resistance. The suitability of different binder rutting parameters for explaining the rutting resistance of unmodified binders as well as modified binders has been a topic of research for several years. Considering that asphalt mixes in pavement layers are subjected to different conditions of temperature, loading time/frequency and stresses/strains, it is expected that these conditions will affect the way binder rutting resistance is judged. This study was conducted to examine the suitability of different binder rutting parameters for ranking of binders (unmodified as well as polymer and crumb rubber modified), distinguish modified binders from unmodified binders and for their ability to correlate with mix rutting. For this purpose, nine binders (four unmodified and five modified) were evaluated in oscillation and creep and recovery modes and various rutting parameters were examined. Oscillation tests were performed at varying frequencies and multiple stress creep recovery test was performed at different stress levels. The binder parameters were correlated with wheel tracking rut depths of bituminous concrete mix with NMAS of 19 mm. The frequency sensitivity of oscillation parameters and stress sensitivity of creep and recovery parameters were examined. Jnr and% recovery have been found to be stress sensitive whereas |G∗|, δ and |G∗|/sinδ were frequency sensitive. Some of the binder parameters have distinctly different ranges of values for unmodified and modified binders. The rankings produced by ZSV and Jnr closely matched the ranking of the mixes identified based on wheel tracking rut depths. While both oscillation and MSCR parameters correlated well with mix rutting for unmodified binder mixes, the correlation of oscillation parameters with mix rut depth was not good for modified binder mixes.