Comparative Low-Temperature Flexural and Creep Responses of Two SBS-Based Asphalt Mixture Formulations

This study compares the low-temperature responses of two SBS-based asphalt mixtures under progressive step loading: a 4% SBS-modified control mixture and a composite mixture containing 3% SBS + 1.0% Nano-SiO2. Progressive three-point bending creep tests were conducted at 0 °C, −10 °C, and −20 °C to evaluate their mechanical and time-dependent responses. Furthermore, a reduced offset-power-law equation motivated by the first-order small-argument expansion of the fractional-order representation was calibrated to the recorded within-stage creep curves and subsequently used for a model-based time-domain interpretation. The reduced equation captured the main features of the recorded within-stage curve shapes under the tested conditions and provided stage-specific descriptors for comparing the recorded time-dependent responses. In the retained records, the measured flexural tensile strength and maximum flexural tensile strain values were higher for the composite formulation than for the 4% SBS-modified control under the tested temperature conditions. Under the tested step-loading conditions, the retained stage curves showed formulation-dependent within-stage displacement responses. The observed differences are interpreted at the formulation-comparison level rather than as isolated Nano-SiO2 effects. The comparison is limited to the retained records for the two prescribed formulations at the common 5.2% asphalt-to-aggregate ratio and does not quantify between-specimen variability. Together, the measured flexural indicators and model-derived stress-retention responses describe a temperature-dependent balance among deformation accommodation, flexural resistance, and modeled stress retention.