Optimization of composite filler based on asphalt-filler interaction for enhanced road performance of asphalt mixtures

Although fillers constitute a small proportion in asphalt mixtures, their enormous specific surface area makes them a critical factor influencing asphalt-filler interfacial interactions, directly determining the mixture's resistance to high-temperature deformation, moisture damage, and fatigue. Conventional fillers like cement face issues such as agglomeration. Developing high-performance composite fillers is therefore significant for enhancing pavement durability. This study systematically evaluated the interfacial interaction between asphalt and five fillers (cement, slaked lime, red mud, steel slag, mineral powder) using the rheological parameter C. The novelty of this work is its ability to predict the comprehensive road performance of composite fillers from a fundamental interfacial parameter (C-value), thereby enabling a scientific optimization of the formulation rather than relying on empirical trial-and-error. After identifying high-performance fillers, the effects of composite fillers on the road performance of porous asphalt mixtures were analyzed using rutting tests, immersion Cantabro tests, and four-point bending fatigue tests. Results showed that slaked lime significantly enhanced interfacial interactions, with its C-value increasing by 31.8% compared to mineral powder. Road performance tests demonstrated that with increasing slaked lime content, the dynamic stability improved by up to 60.9%, immersion Cantabro loss decreased by over 40%, and fatigue resistance peaked at a 40% dosage with a 47.0% increase in fatigue life. Comprehensive performance analysis indicated that the 40% slaked lime + 60% mineral powder formulation achieved synergistic optimization. This study confirms that the 40% slaked lime composite filler significantly enhances the comprehensive road performance of asphalt mixtures. The findings provide a direct and practical material formulation (40% SL + 60% MP) for designing more durable drainage asphalt pavements, offering a reliable solution to extend service life and improve sustainability.