Nanomaterial and fatigue cracking of hot mix asphalt

Fatigue cracking is the main form of structural damage in flexible pavements. One of the convenient approaches for decreasing this type of distress in hot mix asphalt (HMA) is use of nanomaterials as additives in asphalt mixtures. In this study, the effects of using nano zinc oxide (ZnO) on fatigue cracking of asphalt mixtures have been evaluated by determining the mechanism that affects the asphalt cement's (AC's) cohesion and the adhesive bond between aggregate and AC using the surface free energy (SFE) method and indirect tensile fatigue test. The HMA mixtures containing 1%, 3%, 5%, and 7% of nano ZnO are plant prepared with one source of granite aggregate, and one type of AC with 85/100-penetration grade. The results showed that fatigue lives of mixtures containing nano ZnO were higher than those of the control mixtures. This is attributed to the fact that adding nano ZnO leads to decrease of the acid component of SFE and increase of the basic component in SFE of the AC that enhances the adhesion between AC and aggregate. Furthermore, the asphalt mixtures made with the modified AC showed greater fatigue life than the control mixtures due to improved cohesion energy and higher resistance to fatigue cracking in asphalt film.