Influence of graft-activated crumb rubber on the aging performance of modified bitumen: Experimental analysis and molecular dynamics simulation

Abstract

This paper centers on the assessment of how graft-activated crumb rubber (GR) affects the aging properties of modified bitumen. Three bitumen samples, namely matrix bitumen (MB), crumb rubber modified bitumen (CB) and graft-activated crumb rubber modified bitumen (GB) were aged by rotating thin film oven test (RTFOT) and pressure aging vessel (PAV). The physical and rheological performance of the bitumen were assessed before and after aging, and the aging mechanism was analyzed using Fourier-transform infrared spectroscopy (FTIR) and molecular dynamics (MD) simulation. The results indicated that GR significantly improved bitumen performance in both high and low temperatures after being aged, enhancing its anti-aging properties. This positive effect was attributed to the physical swelling of GR in bitumen and chemical reactions between the amide group in GR and the anhydride group in bitumen. These reactions depleted the polar molecular content in bitumen, reducing its susceptibility to oxidation. A comparison of FTIR results between CB and GB demonstrated the absence of the anhydride group and reduced levels of the carbonyl index (CI) and sulfoxide index (SI) in GB, confirming the occurrence of chemical reactions. MD simulations further revealed that GB exhibited the highest fractional free volume (FFV) after being aged and displayed inferior agglomeration behavior towards light components compared to crumb rubber (CR). In conclusion, the combined experimental and analytical findings collectively affirmed that the primary factor contributing to the enhanced anti-aging properties of GB was the chemical reaction between GR and bitumen.