Development of the Criteria for Optimum Filler–Binder Ratio in an Asphalt Mix Based on Fatigue Performance

This research aims to propose a framework for selecting the optimum filler–binder (F-B) ratio in an asphalt mixture, with the objective to achieve desired fatigue performance at the lowest possible binder content. The asphalt mixtures were prepared with two types (VG-30 and PMB-40) of binders and three waste fillers (red mud, marble dust, and limestone dust), at varying filler contents (3%, 5%, and 7% by weight of aggregates). The fatigue resistance of the mixtures was quantified by the critical strain energy release rate ($J_c$), obtained from semicircular bending test. The results indicate that the fineness modulus, specific surface area, and Rigden voids were the primary filler characteristics influencing the behavior of unmodified mixtures, whereas the role of binder was determinant in the modified mixtures. Based on the findings of the study, it is proposed that the parameter $\mathrm{F}\mathrm{S}\mathrm{R}/|G^{*}|·\sin \delta$ (where FSR is the ratio of fineness modulus and the product of specific surface area and Rigden voids, and $|G^{*}|·\sin \delta$ is a rheological parameter of the asphalt binder) can be used to estimate the optimum F-B ratio during the mix design of asphalt mixtures.