Use of engineered pellets containing E-cigarette butts and a recycling agent for stone mastic asphalt mixtures incorporating recycled asphalt

This study introduces a double-recycling approach by incorporating Reclaimed Asphalt Pavement (RAP) and E-cigarette butts (E-CBs) into Stone Mastic Asphalt (SMA) mixtures, aimed at enhancing sustainability in the pavement industry. While the commonly used method involves the direct addition of recycling agents to asphalt mixtures, this study explores the encapsulation of recycling agents within fibre pellets. To evaluate this approach, two fibre pellets were produced from E-CBs using 3D printed tube moulds: Pellet I, containing only E-CBs, and Pellet II, comprising E-CBs combined with a recycling agent. Three mixtures with 40 % RAP were prepared for evaluation: one utilizing Pellet II; and the other two containing either Pellet I or cellulose fibre, both with recycling agents added directly. A non-RAP mixture using cellulose fibres was selected as control. The cellulose fibre content was 0.3 %, while shredded E-CBs in Pellet I or II was set at 0.4 % by aggregate weight. Based on the mixtures tested in this study, results revealed that all RAP-containing mixtures exhibited higher compactability, tensile strength, stiffness, and fatigue resistance compared to the non-RAP mixture, with excellent water resistance across all samples. Notably, the encapsulated recycling agent in Pellet II enhanced fatigue performance, with P2RAP showing a fatigue life approximately six times that of P1RAP at a 1.5 kN load amplitude, while maintaining workability, tensile strength, stiffness, rutting resistance and low-temperature cracking resistance similar to the traditional method of adding recycling agents. These findings highlight the effectiveness of recycling agent-encapsulated fibre pellets derived from E-CBs in RAP-containing mixtures, with potential improvements in fatigue resistance.