Rheological and Chemical Investigation on the Damage and Healing Properties of Bituminous Binders

In order to optimize the performance of flexible pavements, one of the key issues which has to be addressed is the characterization and selection of bituminous binders with respect to their capability of contributing to fatigue resistance. In such a context, there is currently the need of developing and validating test protocols and analysis procedures which may enhance the understanding and quantitative description of the two phenomena which underlie fatigue: microcrack damage and healing. In this paper the Authors present the results obtained during an experimental investigation which addressed the abovementioned issues in the case of several unmodified bituminous binders sampled from different refineries. The objective of the study was to highlight the relationships which may exist between the composition and structure of the binders and their fatigue and healing properties. This required the combined use of thin-layer chromatographic analyses and specifically-developed rheological test protocols, which may be run in the oscillatory mode by using a standard dynamic shear rheometer. It was observed that clear correlations can be found between the two sets of test results. Binder fatigue life is directly linked to the colloidal instability index, while the relative healing index, introduced to quantify the stiffness gain which occurs during rest periods, can be expressed as a function of the ratio between saturates and aromatics. Both relationships, to be validated by further investigations, may be especially useful in the preliminary screening of binders with respect to their fatigue properties.