Rheology-Driven Quantification and Mechanistic Insight into Binder-Filler Interactions in Asphalt Mastics Incorporating Raw and Calcined Oyster Shell Powders

Waste oyster shell powder (OP) and calcined oyster shell powder (COP) were used as bio-fillers in asphalt mastics. Limestone powder (LP) served as the control. This study employed rheological theory to quantify filler–asphalt interactions. Dynamic shear rheometry (DSR), Black diagrams, and master curves were analyzed to determine critical volume fraction (φcrit), interaction parameter (C), and complex viscosity increment (∆η*). Results indicate that OP mastics exhibit the lowest φcrit (0.510) and highest C value (1.133), demonstrating the strongest interfacial interaction. COP shows intermediate interaction strength (φcrit = 0.542), yet both OP and COP outperform LP (φcrit = 0.617) in high-temperature deformation resistance within the 0.23–0.53 filler volume fraction range, evidenced by superior complex shear modulus (G*) master curves and pronounced ∆η* increases. Grey relational analysis identifies specific surface area and CaCO3 content as governing factors. Optical microscopy and FTIR confirm that filler–asphalt interactions are dominated by physical adsorption without chemical bond formation. These findings elucidate the performance advantages of both raw and calcined oyster shell powders and provide a theoretical basis for their application as sustainable high-performance bio-fillers in asphalt pavements.