Confined crushing of recycled concrete aggregate: Fractal gradation, loose-bulk-density response, and mix-specific concrete use

Vertical active loading–passive lateral confinement (VAL–PLC) was evaluated at bench scale for recycled-concrete-aggregate gradation, loose bulk density, and use in one concrete mixture. In 34 single-pass runs, 88.753kg of 99.312 kg (89.37%) was at or below 9.5 mm; a complete-run bootstrap gave a 95% percentile interval of 84.26%–94.11%. Across 32 block-feed batches, pan-included full-observed-support fits gave D = 2.312 ± 0.067 and R² = 0.955 ± 0.054; after pan exclusion, the corresponding means were 2.329 ± 0.048 and 0.985 ± 0.007, showing endpoint dependence. Seventy-one prescribed- D gradations were each tested in triplicate. The 40 levels from D = 2.31 to 2.70 had an unweighted mean loose bulk density of 1514.49 kg·m⁻³ ( SD across levels = 8.86 kg·m⁻³). Retaining the pooled EP2 product at or below 9.5 mm yielded 46.384 kg (64.03%). In one fixed fully recycled concrete formulation using this blend as the sole aggregate, the mean 28 d equivalent 150-mm cube compressive strength was 61.7 ± 1.1 MPa (mean ± sample SD; n = 3 specimens from one batch). These results support a condition-specific comparison domain and mix-specific feasibility, not industrial-scale performance or an independent aggregate effect.