Researchers have developed a novel dual-recycling method that incorporates reclaimed asphalt pavement (RAP) and e-cigarette butts (E-CBs) into stone mastic asphalt (SMA) mixtures using encapsulated fiber pellets to improve pavement performance and sustainability.
Study: Use of engineered pellets containing E-cigarette butts and a recycling agent for stone mastic asphalt mixtures incorporating recycled asphalt. Image Credit: Master_foto/Shutterstock.com
Published in Construction and Building Materials, the study explores an alternative to traditional recycling methods, which typically involve directly adding recycling agents to asphalt mixtures. Instead, the researchers investigated the effectiveness of encapsulating these agents within fiber pellets, offering a more controlled and potentially efficient delivery system.
Background
As the road construction industry continues to emphasize sustainability and circular economy practices, interest in reusing waste materials is on the rise. Among them, RAP remains the most widely used recycled material in pavement engineering. However, one persistent challenge is the deterioration of the bituminous binder in RAP, which weakens fatigue performance and increases the risk of cracking under low temperatures.
To address this, recycling agents—designed to restore the binder’s flexibility—are commonly added during mixing or through encapsulation. At the same time, fiber pellets are routinely used in SMA mixtures, yet their potential as carriers for rejuvenators hasn’t been thoroughly investigated. This study sets out to explore that gap by assessing whether E-CB-derived fiber pellets can effectively deliver recycling agents in high-RAP asphalt mixes.
Methods
As part of the study, the researchers developed two types of fiber pellets using 3D-printed molds:
- Pellet I, composed solely of E-CBs (0.4 %)
- Pellet II, containing E-CBs (0.4 %) combined with a recycling agent
Using a gap-graded aggregate structure and high binder content, three SMA mixtures with 40 % RAP were prepared:
- One using Pellet II
- One using Pellet I with a recycling agent added directly
- One using cellulose fiber (0.3 %) witha recycling agent added directly
A non-RAP control mix with cellulose fiber served as the benchmark.
All mixtures were compacted into cylindrical specimens and tested for key physical and mechanical properties, including volumetric analysis, indirect tensile strength (ITS), stiffness modulus (ITSM), tensile strength ratio (ITSR), and rutting resistance using the Hamburg wheel tracking (HWT) test. Roller-compacted slabs were also produced and sawn into prismatic samples for thermal stress restrained specimen testing (TSRST) and fatigue asphalt cracking testing (FACT). Compaction levels were calibrated using Marshall samples to ensure consistent density across slabs.
Results and Discussion
The RAP-based mixtures consistently outperformed the control in terms of compactability, strength, stiffness, and fatigue resistance. After 100 gyrations, they showed fewer air voids and strong resistance to water damage, as confirmed by ITSR and HWT results.
Among the RAP mixtures, the one using Pellet II—with the recycling agent encapsulated—delivered the most notable improvements in fatigue life, lasting nearly six times longer than the mixture with Pellet I. Performance metrics such as stiffness, tensile strength, rutting resistance, and low-temperature cracking resistance were comparable to those achieved through traditional rejuvenator dosing methods.
While RAP mixtures showed roughly double the tensile stiffness modulus of the control (due to the presence of aged binder), the difference between Pellet I and Pellet II in stiffness and rutting performance was minimal—indicating that the delivery method has limited impact on those specific attributes.
In TSRST, the control mix showed the lowest fracture temperature, indicating slightly better low-temperature performance, but the fiber pellet mixes followed closely, with similar fracture points around –22 °C.
FACT testing further highlighted the structural advantages of RAP-containing mixtures. Despite being more brittle than the control, these mixes endured more load cycles before cracking, demonstrating improved fatigue resistance without sacrificing long-term durability.
Conclusion and Future Prospects
This study confirms the feasibility of using fiber pellets made from E-CBs—especially those encapsulating recycling agents—in SMA mixtures with high RAP content. These engineered pellets improved fatigue resistance while maintaining solid physical and mechanical properties.
The researchers recommend further optimizing pellet fabrication or increasing recycling agent content to enhance performance. They also suggest exploring additional recycled materials alongside E-CBs to support more sustainable, resource-efficient practices in pavement construction.
Journal Reference
Guo, Y., Tataranni, P., Moreno-Navarro, F., Martínez, R. T., & Sangiorgi, C. (2025). Use of engineered pellets containing E-cigarette butts and a recycling agent for stone mastic asphalt mixtures incorporating recycled asphalt. Construction and Building Materials, 483, 141832. DOI: 10.1016/j.conbuildmat.2025.141832. https://www.sciencedirect.com/science/article/pii/S095006182501983X
Disclaimer: The views expressed here are those of the author expressed in their private capacity and do not necessarily represent the views of AZoM.com Limited T/A AZoNetwork the owner and operator of this website. This disclaimer forms part of the Terms and conditions of use of this website.