Abstract

Bituminous materials in roads are subjected to short-term loading each time a vehicle passes. If sufficiently high, the loading results in a loss of rigidity of the material and can, by accumulation in the long term, lead to failure. The resulting fatigue deterioration is of great importance in pavement construction and must be correctly understood in order to ensure adequate structural design. The binder property plays a major role in determining the mechanical characteristics in asphalt pavement to resist distress. This paper presents results of an investigation to evaluate the effects of fume silica, ground slug and two types of styrene-butadiene-styrene (SBS) on the fatigue performance of local bituminous binders. These additives were incorporated into asphalt binder from two different sources, namely Nasiriyah and Durah refinery in the middle and southern regions of Iraq. This study adopts a time sweep (TS) test method to study the fatigue phenomenon under controlled strain and stress modes using a dynamic shear rheometer (DSR). Fatigue life of the asphalt binder is defined using the traditional approach based on number of cycles required to cause to failure and reduction in initial stiffness. To accurately predict the fatigue life of modified and unmodified binders, the viscoelastic continuum damage (VECD) approach and energy approach have been also adopted. It was found that additives had a superior performance in terms of fatigue life. However, the energy approach has been shown to be more realistic in predicting the fatigue life of modified binders than the VECD approach as the latter did not correlate well with traditional and energy approaches. It can be concluded that the fatigue performance of Durah asphalt binder is better than that of Nasiriyah in all cases with or without adding additives. Adding 2% silica fume and 6% SBS 1184 enhanced the fatigue performance of local asphalt.

Key words: Asphalt binder, fatigue performance, time sweep test, viscoelastic continuum damage (VECD), dissipated energy, plateau value, energy ratio, and energy stiffness ratio.