Mechanical evaluation of the fine aggregate matrix in complete asphalt mixtures incorporating boiler ash

The premature degradation of asphalt pavements, characterized by permanent deforma- tions and fatigue cracking, represents a critical challenge for transportation infrastructure, particularly in tropical regions subject to heavy traffic loads and significant thermal variations. This study investi- gates the mechanical performance of Fine Aggregate Matrices (FAM) produced with boiler ash as an alternative filler material, comparing them to conventional formulations. Rheological tests performed using a Dynamic Shear Rheometer (DSR) demonstrated that the addition of 3% ash increased the dynamic modulus from 6.47 GPa to 9.71 GPa (a 50% increase) at 15°C and 25 Hz, while at 45°C the complex modulus increased from 121.3 MPa to 246.7 MPa. Multiple Stress Creep Recovery (MSCR) tests indicated enhancements in elastic recovery, increasing from 90.68% to 93.33% under 0.1 kPa and from 78.15% to 83.57% under 3.2 kPa, alongside substantial reductions in non-recoverable compliance ( J nr ), which declined by 42% and 60%, from 13.99 × 10 −6 to 8.09 × 10 −6 kPa -1 (0.1 kPa) and from 236.27 × 10 −6 to 94.10 × 10 −6 kPa -1 (3.2 kPa), respectively. These results confirm that boiler ash enhances stiffness and rutting resistance under thermomechanical loading conditions. However, fa- tigue testing revealed that, although stiffness and rutting resistance improved, the material exhibited accelerated modulus degradation under cyclic tensile loading, resulting in a reduction in fatigue life. This underscores a trade-off between enhanced deformation resistance and diminished fatigue performance. Therefore, the application of this material is more appropriate for pavement layers where rutting resistance is the primary design requirement and the fatigue demand is comparatively lower. The adopted methodology, centered on FAM-level characterization, enabled the identifica- tion of performance trends not captured in full asphalt mixture testing, emphasizing the value of multiscale analysis in the development of advanced materials for transportation infrastructure