Toward Carbon-Negative and Emission-Curbing Roads to Drive Environmental Health

Roadway infrastructures are exposed to solar ultraviolet (UV) radiation during their service life. UV rays generate free radicals that diffuse deep into bitumen layers, accelerating the aging and degradation of bituminous composites. Here, we hypothesize that carbonaceous particles grafted by bioderived molecules such as amines and amides can serve as scavengers of free radicals, delaying aging in bituminous composites. To test this hypothesis, we use laboratory experiments and molecular dynamics simulations to compare the efficacy of biochars made from woody biomass and algal biomass in delaying the aging of bituminous composites. We further examine the underlying molecular mechanisms that delay aging by computing the extent of diffusion of free radicals through an amorphous graphite film in the pristine form and in amine- and amide-functionalized forms. The laboratory results indicate that algal biochar is considerably more effective than woody biochar in delaying aging. The simulation results corroborate laboratory findings showing that even at low concentrations, surface functionals such as amines and amides considerably enhance the efficacy of pristine carbon in shielding the underlying layers against the diffusion of free radicals such as hydrogen peroxide (H2O2). At high concentrations (e.g., 10 wt %), amines were found to be more effective than amides in reducing the diffusion rate of H2O2. This indicates that the scavenging efficacy of carbonaceous particles can be optimized by proper biografting. The algae that were used to make functionalized carbonaceous particles in this study are a means to capture CO2 from air. Therefore, our findings contribute to extending the sustainability of highway infrastructures while moving toward carbon-negative and emission-curbing roads to promote environmental health.