Optimal mix proportion of high-strength fully recycled coarse aggregate concrete considering performance, environmental impact and cost

High-strength fully recycled coarse aggregate concrete (HSFRCAC) shows promising prospects in civil engineering. Well-determined mix proportions considering workability, strength, environmental impact (EI) and cost are essential for promoting HSFRCAC in practice. Existing mix design methods for high-strength recycled aggregate concrete mainly optimise strength or workability. Studies simultaneously considering performance, EI and cost are lacking. In this work, an orthogonal experiment based on the dense mix design algorithm was conducted to evaluate the influence of mix parameters on workability, compressive strength, EI and cost of HSFRCAC. An optimal mix proportion was finally determined based on a multi-criteria comprehensive evaluation. The results showed that the primary factors affecting workability, strength, EI and cost are, respectively, the paste–aggregate ratio (p/a), the sand ratio (SR), fly ash (FA) content and p/a, respectively. The optimal mix proportion was for SR = 0.55, p/a = 0.35/0.65, 6% silica fume, 18% FA, maximum aggregate particle size of 10 mm, indoor curing and a traditional mixing approach. The optimal mixture achieved a slump-flow of 411 mm, strength of 88.1 MPa, environmental comprehensive index of 8.20 × 10⁻¹²/year per cubic metre and a cost of 656.67 CNY/m³. The highest compressive strength reached 96.8 MPa and its comprehensive performance ranked second among all the mix proportions evaluated.