Functionalized graphene reduces asphalt aging through specific anti-aging mechanisms

Graphene, a carbon-based nanomaterial, is demonstrating potential to significantly slow the aging of asphalt binders, according to recent research by a team of Chinese scientists. The study, published in Case Studies in Construction Materials, highlights how polyvinylpyrrolidone-functionalized graphene (PGR) can reduce the effects of thermal oxidation and ultraviolet (UV) exposure on asphalt. The research focused on two types of asphalt binders: a neat 70-penetration-grade asphalt (AH-70) and the same asphalt modified with styrene-butadiene-styrene (SBS), a common polymer modifier.

The researchers, led by Jingwen Liu, explored how PGR interacts with these binders under controlled aging conditions. They found that the optimal dose of graphene varies depending on the binder matrix, with no universal dosage applicable across different formulations. The study utilized a rolling thin-film oven test followed by UV exposure to simulate aging, revealing that PGR can significantly enhance the durability of both neat and SBS-modified asphalt binders.

The PGR was prepared by reducing graphene oxide and adsorbing polyvinylpyrrolidone onto the graphene surface. This process prevents the graphene sheets from restacking and enhances their compatibility with asphalt. The resulting material had a high carbon content and low residual oxygen, crucial for maintaining stability and interaction with the asphalt binder.

In neat asphalt, PGR was added at various concentrations, with 1.0 percent by weight showing the most improvement in reducing viscosity aging and maintaining ductility. For the SBS-modified system, a lower concentration of 0.3 percent PGR was optimal, offering significant protection against UV-induced degradation. The study's multiscale characterization techniques, including atomic force microscopy and gel permeation chromatography, provided insights into how PGR stabilizes the asphalt matrix.

Chemical analysis showed that PGR effectively reduces the formation of oxygen-containing functional groups, such as carbonyls and sulfoxides, which are indicators of aging. In the SBS system, PGR also protected the polymer's unsaturated segments from degradation. The research suggests that PGR acts as a barrier, slowing oxygen permeation and stabilizing the polymer-rich phase, which is crucial for maintaining binder performance.

The study underscores the importance of precise dosing of PGR for different asphalt formulations to optimize performance without compromising workability or flexibility. While the research provides promising insights, the authors note that further studies are needed to translate these findings into practical applications for pavement design, particularly in extreme climates where UV resistance is critical.