Innovative scratch test to evaluate the effect of chemical additives on warm mix asphalts

This study investigates the role of commercial additives generally used in Warm Mix Asphalt through a multidisciplinary approach based on an innovative scratch resistance testing in combination with rheology and surface energy analysis. Contrary to conventional assumptions, the experimental test campaign demonstrates that additives do not significantly alter the bulk viscosity or temperature sensitivity of styrene-butadiene-styrene polymer-modified bitumen, as evidenced by dynamic shear rheometry and Walther-Saal modeling. Instead, their efficacy arises from interfacial modifications as proved by contact angle measurements and surface energy decomposition which reveal a marked reduction in the polar component and an increase in the dispersive component, enhancing bitumen-aggregate wettability. An innovative scratch test carried out on basalt and calcareous substrates coated with a bituminous film further elucidated substrate-dependent mechanical responses, with additives improving adhesion and reducing penetration depth, particularly on basalt. The additive rich in amines emerges as the most effective, though its performance is modulated by substrate mineralogy. These findings underscore a molecular-level mechanism where surfactants act as interfacial lubricants, optimizing workability at reduced temperatures without compromising mechanical integrity. The study advances the rational design of warm mix asphalt by linking macroscopic performance to nanoscale surface phenomena, offering a pathway to energy-efficient, high-performance asphalt formulations.