Abstract: The performance of asphalt mixtures is strongly influenced by the behaviour of mastics, yet the intrinsic properties of fillers are seldom integrated into mixture design. This study evaluates mussel shell powder (SP) as a sustainable filler alternative to rock powder (RP) and Portland cement (PC) through a multiscale framework linking filler characteristics to mastic rheology and mixture performance. Physical, chemical, and morphological properties of the fillers were characterised and related to mechanical responses under fatigue, permanent deformation, and moisture damage. PC mastics exhibited the highest stiffness and recovery, reducing Jnr by up to 90% relative to the base binder, while RP maximised the instantaneous modulus E 1. SP showed intermediate behaviour, achieving Jnr reductions of approximately 89% and recovery levels comparable to RP. In mixtures, PC achieved the highest fatigue lives at low-intermediate strain levels, RP provided superior rutting resistance ( RDw ? 1 mm), and SP delivered responses within the range of the conventional fillers in both Hamburg wheel-tracking and creep tests. SP also maintained ITSR values close to 80%, indicating competitive moisture resistance. The findings indicate that filler basicity, Rigden voids, morphology, roughness, and particle-size polydispersity govern mastic rheology and contribute to mixture durability under the tested conditions. While the results highlight clear trends, they also reflect the variability inherent to fatigue and moisture performance. Overall, mussel shell powder demonstrates the potential to serve as a sustainable filler alternative, supporting its incorporation into future bituminous material design frameworks.
