Asphaltite Ash as a Mineral Filler in Bitumen: Physical, Rheological and Microstructural Assessment

Mining wastes represent a significant environmental challenge due to their large volumes and limited reuse potential. This study evaluates combustion-derived asphaltite ash (AA) as a mineral filler in bituminous binders through physical, rheological, thermal, chemical, and microstructural characterization. AA was produced by laboratory combustion of asphaltite at 1000 °C and incorporated into a B 50/70 binder at contents of 0, 2, 4, 6, and 8 wt % relative to the initial mass of the base binder. Penetration, ductility, and elastic recovery decreased, whereas the softening point increased with AA incorporation. Rotational viscosity decreased at 135 °C but increased at 165 °C relative to the control at the same temperature. Among the tested contents, AA4 exhibited the highest unaged rutting parameter and failure temperature of 78.9 °C, compared with 77.3 °C for the neat binder. However, AA4 also showed the highest stiffness to m-value ratio at -12 °C, indicating a less favorable low-temperature response. SEM-EDX and FTIR observations support a predominantly physical filler action associated with particle dispersion and mineral-phase incorporation, without demonstrating chemical bonding or cross-linking. AA4 exhibited the highest measured thermal degradation temperatures, while the residual mass increased with AA content because of the inorganic nature of the filler. These findings classify AA as a mineral filler and identify 4% AA as a candidate content for further high-temperature evaluation, rather than as a general optimum.