Fibre pellets incorporating e-cigarette butts and organic additive for warm Stone Mastic Asphalt mixtures

Warm Mix Asphalt (WMA) technology has been widely adopted to reduce production and compaction temperatures while maintaining satisfactory pavement performance. However, the effects of different methods of adding WMA additives, particularly organic additives, on the performance of Stone Mastic Asphalt (SMA) have not yet been fully explored. This study investigates a sustainable method for producing SMA using WMA technology by incorporating a Fischer-Tropsch wax via a dry method using pelletized fibres manufactured from waste e-cigarette butts (E-CBs). The proposed approach was compared with the conventional wet method, in which the Fischer-Tropsch wax was pre-blended with bitumen prior to mixing. Both SMA mixtures were produced at reduced temperatures, and their volumetric properties and mechanical performance were systematically evaluated. The results show that the WSMA-CF mixture produced via the wet method exhibited better compactability, higher indirect tensile strength, higher stiffness modulus, and improved resistance to low temperature cracking. In contrast, incorporating the wax additive within the pelletized fibres shows a limited influence on fatigue cracking performance. Although the dry method demonstrates potential for sustainable warm SMA production by enabling the reuse of waste E-CBs and simplifying additive incorporation, further optimization is required to enhance mechanical performance, particularly with respect to moisture susceptibility and resistance to permanent deformation.