Multi-scale experimental and modeling assessment of mechanical-thermal trade-offs in self-compacting concrete with high-volume coarse reclaimed asphalt pavement

Abstract

The massive accumulation of reclaimed asphalt pavement (RAP) and the growing demand for energy-efficient materials offer a strategic opportunity for sustainable concrete. This study investigates the feasibility of complete substitution of natural coarse aggregates (NCA) with coarse RAP in self-compacting concrete (SCC) through a multi-scale experimental and micromechanical modeling approach. Fresh-state assessment confirmed that self-compacting behavior was preserved; however, the hydrophobic nature of the residual bitumen increased yield stress by 53.4% by hindering interfacial lubrication. Microstructural analysis revealed that this hydrophobic coating promotes a debonded interfacial transition zone, causing a 30.1% reduction in static elastic modulus. Micromechanical modeling captured this degradation, identifying the ‘effective RAP inclusion’ as a lower-stiffness phase, approximately 2.5 times less stiff than NCA. Despite these alterations, the 100% RAP-based SCC mixture retained a robust 28 d compressive strength of 40 MPa, satisfying C30/37 structural requirements. Crucially, this mechanical limitation was offset by a functional gain: a 19% reduction in thermal conductivity (to 1.53 W (m·K)−1). A decoupled modeling framework provided definitive evidence that this improvement is not a porosity artifact but is predominantly driven by the intrinsic thermal barrier effect of the bituminous coating. Overall, this work demonstrates that coarse RAP acts as a functionalizing agent, transforming an inherent mechanical limitation into a valuable thermal asset. High-volume coarse RAP-based SCC thus emerges as a promising high-performance, eco-efficient material for sustainable, energy-efficient structural applications.