This paper presents an investigation on the permanent and resilient deformation behaviour as well as the shear and physical properties of different RCA, sourced from demolished buildings (RCAB1 and RCAB2) and concrete pavement (RCAP). Monotonic triaxial tests and repeated load triaxial tests (RLTT) were performed to determine respectively their failure resistance and the cyclic behaviour, modelled with the Boyce model and the DBGSP model. In addition, the physical properties and water absorption kinetics of aggregates were studied and compared with the existing standard. The results indicated that all RCA have admissible physical properties and can be used in pavement base and subbase layer. However, the RLTT revealed that the use of concrete wastes with low strength and containing high amount of rounded particles (RCAP in this study) can lead to poor performance of pavement, which should be limited in the pavement construction.

Phosphogypsum (PG) and Carbide Slag (CS) are two industrial byproducts that can be used as cementitious materials, and their synergistic effect provides excellent activation of ground granulated blast furnace slag (GGBS), which is traditionally activated by lime (LM). However, the behavior of PG-GGBS-CS ternary blended cement remains largely unexplored. In this study, the mechanical performance, hydration mechanisms, and environmental profile of PG–GGBS–CS binders in comparison with PG–GGBS–LM were evaluated by unconfined compressive strength (UCS), XRD, SEM, and TGA analyses. The optimum formulation containing 30% PG achieved 24.88 ± 1.24 MPa at 28 d, statistically comparable to 25.6 ± 1.28 MPa for PG–GGBS–LM. The synergistic activation of PG and CS/LM on GGBS has been identified as a crucial factor in the strengthening of UCS in ternary blended cement. Hydration products consisted mainly of calcium silicate hydrate (C–S–H) gels and Ettringite (AFt). Importantly, the CO₂ footprint of PG–GGBS–CS was reduced by 3.2% compared to that of PG–GGBS–LM. These findings establish CS as an effective substitute for lime in eco-binders, combining technical efficiency with carbon mitigation and offering a viable pathway for large-scale valorization of hazardous industrial residues.