Optimization design of low-carbon hybrid concrete containing slag and limestone powder

Slag and limestone powder are common mineral admixtures to produce environmentally friendly concrete. This paper presents an optimal design method for low-carbon concrete containing slag and limestone powder that considers the influence of strength (30, 40, 50 MPa), carbonation service life (50, 100 years), and CO₂ concentration of microclimate (0.04% and 0.052%). By using a genetic algorithm to determine the global optimal solution that satisfies different constraints, the optimal mixtures and decisive factors of a concrete mix can be found. The analysis results are as follows: (1) When the carbonation service life is 50 years, the durability of carbonation is the decisive factor for designing concrete with ordinary strength (30 MPa), but for medium strength (40 MPa) and high strength (50 MPa) concrete, strength is the decisive factor. (2) When carbonation service life is 100 years, for ordinary (30 MPa) and medium strength (40 MPa) concrete, carbonation durability is the decisive design factor, while for high-strength concrete (50 MPa), it is compressive strength. (3) As carbonation durability is the decisive design factor, when the CO₂ concentration of microclimate increases from 0.04 to 0.052%, the real strengths of concrete increase from 44.34 to 48.53 MPa. (4) The relations between CO₂ emissions and compressive strengths and between water-binder ratios and compressive strengths of the optimized concrete design were consistent with the project, which proved the effectiveness of the proposed method.