Morphological and nanomechanical analyses of ground tire rubber-modified asphalts

Automobile industries produce more than 5.2 million tons of scrapped tires each year in the United States. Disposal of such a huge amount of waste scrapped tires has become a serious environmental issue. Scopes to use scrapped tires in the form of Ground Tire Rubber (GTR) in pavement industry have been analyzed in recent years. The GTR has potential to improve hot mix asphalt’s performance from the view points of stiffness, resilience and shock absorbance properties. On the other hand, in recent years, researchers have attempted to explain performance of asphalt in terms of its nanomechanical characteristics. In this study, the PeakForce Quantitative Nanomechanical Mapping (PFQNM™) mode of an atomic force microscope has been employed to find basic nanomechanistic properties and the morphology of GTR-modified asphalt binders. A performance grade (PG) binder (PG 64-22) modified with two different grades of GTR (Mesh #30 and Mesh #40) samples have been evaluated in this study. Nanomechanical properties such as adhesion, energy dissipation, deformation, and DMT (Derjaguin, Muller, and Toporov) modulus for the GTR-modified binders have been quantified. Each sample was scanned for three different (5 × 5, 10 × 10, and 20 × 20 µm) areas. The PFQNM™ analyses revealed distinct microstructures and grain distributions among tested additive modified binder samples. Two distinct phases, namely Catana and Peri-phase, were observed in GTR-modified samples, although the DMT moduli were found to be in a close range in these areas. The neat binder showed another phase, named Perpetua, which was missing from the GTR-modified samples. It was observed that modification of asphalt by addition of GTR considerably changes the mechanistic properties of the base binder.