Nano–micro interfacial study of bitumen–GGBS systems and their mechanical performance in bituminous mixes

The rapid expansion of road infrastructure and parallel depletion of natural aggregates have intensified a need for sustainable alternatives in bituminous pavement construction. Simultaneously, large volumes of Ground Granulated Blast Furnace Slag (GGBS) generate from the steel industry present opportunity for resource valorization. Although GGBS has been widely used as a mineral filler, interfacial interaction with bitumen and systematic performance as fine aggregate replacement remains insufficiently understood. This study presents a comprehensive multi-scale investigation linking nano-scale interfacial bonding to macro-scale mechanical performance of bituminous mixtures incorporating GGBS (5–25%) with VG40 and PMB40 binder or bitumen. Atomic Force Microscopy (AFM) showed that polymer modification enhance work of adhesion by 35 to 45%, while GGBS exhibited nano-scale bonding comparable to basalt. Surface Free Energy (SFE) analysis confirmed strong thermodynamic compatibility and superior moisture stability of the GGBS–bitumen interface. At the mixture level, mechanical performance improves significantly up to 10–15% GGBS replacement. Marshall stiffness, indirect tensile strength (ITS), and resilient modulus increased notably within this range, while tensile strength ratio (TSR) values consistently exceeded the standard requirements for moisture susceptibility. IDEAL-CT and IDEAL-RT indices also demonstrated enhanced cracking and rutting resistance at moderate replacement level. However, performance reduces beyond 20% replacement due to increased porosity and binder absorption associated with GGBS morphology. The integrated multi-scale analysis establishes 10 to 15% GGBS as the optimum replacement range, providing balanced improvements in adhesion, stiffness, moisture resistance and durability. This work offers a scientific framework for performance-based utilization of GGBS in sustainable bituminous pavements.