Conventional binders cannot meet the current performance requirements of asphaltic pavements due to increase in traffic volumes and loads. Nanomaterials, due to their exceptional mechanical properties, are gaining popularity as bitumen modifiers to enhance the performance properties of the asphaltic concrete. Carbon Nanotubes (CNTs) are one of the most widely used nanomaterials because of their strength properties, light weight, small size, and large surface area. CNT addition results in improved substrate characteristics as compared to other modifiers. Due to high length to diameter ratio, dispersion of CNTs in bitumen is a complex phenomenon. In this study, dispersion of CNTs in bitumen was carried out using both dry and wet mixing techniques, the latter was selected on the basis of homogeneity of the resultant asphalt mixture. Scanning Electron Microscopy (SEM) was used to check the dispersion of CNTs in binder while Fourier Transform Infrared Spectroscopy (FTIR) was carried out to ensure the removal of solvent used for wet mixing. Conventional bitumen tests (penetration, softening point, and ductility), dynamic shear rheometer tests, rolling bottle tests, and bitumen bond strength tests were employed to check the improvement in the rheological and adhesion properties of bitumen while wheel tracker test was used to check the improvement in resistance against permanent deformation of asphalt mixtures after addition of CNTs. Results show that CNTs improved the higher temperature performance and permanent deformation resistance in both binder and mixtures. Improvement in bitumen–aggregate adhesion properties and moisture resistance was also observed.

With the increase in the demand for bitumen, it has become essential for pavement engineers to ensure that construction of sustainable pavements occurs. For a complete analysis of the pavement, both its structural and functional performances are considered. In this study, a novel material (i.e., Graphene Nano-Platelets (GNPs)) has been used to enhance both of the types of pavements’ performances. Two percentages of GNPs (i.e., 2% and 4% by the weight of the binder) were used for the modification of asphalt binder in order to achieve the desired Performance Grade. GNPs were homogeneously dispersed in the asphalt binder, which was validated by Scanning Electron Microscope (SEM) images and a Hot Storage Stability Test. To analyze the structural performance of the GNPs-doped asphalt, its rheology, resistance to permanent deformation, resistance to moisture damage, and bitumen-aggregate adhesive bond strength were studied. For the analysis of the functional performance, the skid resistance and polishing effect were studied using a British Pendulum Skid Resistance Tester. The results showed that GNPs improved not only the rutting resistance of the pavement but also its durability. The high surface area of GNPs increases the pavement’s bonding strength and makes the asphalt binder stiffer. GNPs also provide nano-texture to the pavement, which enhances its skid resistance. Thus, we can recommend GNPs as an all-around modifier that could improve not only the structural performance but also the functional performance of asphalt pavements.

Applications of nanotechnology in the pavement industry have increased rapidly during the last decade in order to enhance a pavement’s sustainability and durability. Conventional asphalt binder generally does not provide sufficient resistance against rutting at high temperatures. Carbon black nano-particles (CBNPs, produced by perennial mountain trees’ carbonization) were mixed into the performance grade (PG) 58 asphalt binder in this study. Conventional asphalt binder tests (penetration, ductility and softening point), frequency sweep, performance grading, and bitumen bond strength tests were conducted to study the enhancement in the properties of asphalt binder. Dynamic modulus and wheel tracking tests were also performed to investigate the effect of CBNPs on asphalt mixture properties. Experimental results demonstrated that preferred dosage of CBNPs in asphalt is 10% by weight of the bitumen. Results of scanning electron microscopy (SEM) and storage stability tests validated homogenous and stable dispersion of CBNPs in the asphalt binder. Asphalt mixtures became stiffer and resistant to rutting at high temperatures by addition of CBNPs in asphalt binder. Significant improvement in bitumen aggregate bond strength was also observed by incorporating CBNPs. It is concluded that CBNPs can be used to effectively enhance the high-temperature performance and consequently the sustainability of flexible pavements.

Heavy-duty electric vehicles (HDEV) pose challenges to flexible pavements. This study evaluated four Illinois pavement structures to quantify HDEV impacts on pavements. Compounding factors included increases in load and acceleration, which escalated critical strains and reduced repetitions to failure. Various distresses were considered: bottom-up cracking, shear-driven top-down cracking, and shear-driven shoving. A proposed framework is presented, which includes a new metric—e-truck adjustment factor—that enables a full truck comparison of internal combustion engine vehicles (ICs) with HDEVs. The driving factor for HDEV’s effect was the additional shear strain in the pavement structure. For pavements with relatively thin hot-mix asphalt (HMA) layers (e.g., low volume and typical thick), the increased load impact was prominent. In addition, the impact adversely affected the subgrade and base layer with higher induced structural rutting. Pavement sections with either a relatively thick HMA layer (e.g., full depth) or supported by a high-modulus layer (e.g., stone matrix asphalt [SMA] overlay on Portland cement concrete) were impacted by the increasing acceleration. In that case, the horizontal shear strain near the surface aligned with the increased longitudinal contact stresses. Hence, determining HDEVs’ impact on pavement should consider battery placement and acceleration increase as well as pavement’s structural configuration, which define governing distresses. Full-depth and SMA-overlay sections displayed an increase in near-surface shearing, which may increase maintenance and rehabilitation frequency or warrant the use of shear-resistant materials. The environmental and economic impacts of the scenarios considered were assessed. HDEVs may reduce use-stage costs due to vehicle design efficiency but may escalate pavement maintenance expenses. In addition, the impact of reduced truckload capacity of HDEVs compared to ICs may warrant additional trips to transport the same amount of freight.

Transportation in the United States is the leading sector for greenhouse gas (GHG) emissions, with its contributions increasing over the years. To achieve the US goal of net-zero emissions in 2050, the Federal Highway Administration has launched several programs to set goals and strategies for reducing the emissions in the transportation sector. Flexible pavements, an integral part of the transportation system, contribute significantly to the sector’s carbon footprint. This study investigates the carbon reduction strategies of various states (Florida, Illinois, New York, Pennsylvania, New Jersey, Massachusetts, California, Texas, South Dakota, and Alaska). In addition, life cycle assessments (LCAs) were conducted to quantify the contribution of asphalt concrete pavements toward the states’ goals. The LCA results, calculated for a lane-mile of pavement, considered materials, construction, maintenance, rehabilitation, and use stages. The results showed that the New Jersey pavement section had the highest energy consumption over its life cycle, while Illinois had the lowest. In addition, the maintenance and use stages accounted for a significant portion of the overall GHG emissions, contributing an average of 92% of the total energy consumed. These impacts were primarily influenced by the pavement’s condition, specifically its roughness and volume of vehicles traveling on it. While current transportation emission reduction strategies focus on curtailing on-road vehicles emissions, this study highlights the significant contributions of pavement structures to overall GHG emissions.

The transportation sector’s relatively large greenhouse gas (GHG) footprint highlights the need for low-carbon strategies at every stage of the flexible pavement life cycle. This study performed a comparative life cycle assessment evaluating alternative options in the materials, construction, use, and maintenance and rehabilitation (M&R) stages. Conventional asphalt binder was replaced with bio-binder derived from wastewater-grown algae. In the construction and use stages, diesel used in construction equipment was substituted with 100% renewable diesel (RD100), biodiesel, hydrogen, electricity, and compressed natural gas. The use stage emissions were quantified across a spectrum of alternative fuel uptake scenarios. The analysis compared three M&R treatments: mill-and-overlay, full-depth reclamation (FDR), and cold in-place recycling (CIR). A sensitivity analysis examined trade-offs between increasing bio-binder substitution and the accompanying reductions in pavement service life. The results showed that replacing conventional binder with bio-binder lowered material-stage emissions from 116 to 47 tnCO ₂ eq at 50% dosage and turned net-negative beyond ∼85% substitution. Switching equipment fuel from diesel to RD100 cut GHG emissions by 80%. Hydrogen and electricity achieved 91.1% and 44.5% savings, respectively. The benefits of using electric powertrains in equipment highly depended on the source of electricity. In the use stage, high electric vehicle adoption on a renewable-heavy grid lowered total emissions by 53%, but the same scenario on a coal-based grid increased them by 25%. Among M&R options, CIR had the lowest GHG burden and FDR the highest. The study demonstrated that every pavement life cycle stage offers clear potential to lower overall GHG emissions when low-carbon alternatives are used.