Unraveling the modification mechanisms of waste bio-oils and crumb rubber on asphalt binder based on microscopy and chemo-rheology

Waste bio-oils and scrap tires as industrial waste streams have caused serious health risks and environmental burdens. This study aims to provide a method for hybrid reuse of both wastes to create bio-modified rubberized asphalt and unravel the underlying modification mechanisms using microscopy and chemo-rheological investigations. This hybrid use mitigates some of the challenges faced when using one of the waste streams such as storage stability. The chemical analysis suggests the deoxidizing and devulcanizing effects of bio-modification on the crumb rubber. Thermal analysis shows the bio-modification on crumb rubber decreases the glass transition temperature of the asphalt binder, thereby enhancing the low-temperature properties as also shown in the rheology through the Glover-Rowe parameter. Environmental scanning electron microscopy demonstrates that crumb rubber alone mainly acts as a particle filler, while phase separation is mitigated after bio-modification. This contributes to the different deformation resistance mechanisms as shown in multiple stress creep and recovery test. The decreased length and stiffness difference of catana domains were observed in the asphalt binder after the addition of crumb rubber and bio-oils using atomic force microscopy. Rheological analysis shows the positive effects of bio-modified asphalt rubber i.e. a more elastic response at high temperatures and a more viscous response at low temperatures. The outcome of this study provides insight into converting the two waste materials (bio-oils and crumb rubber) into valuable resources for pavement construction to ensure the sustainability of transportation environments.