Economic and Carbon Emission Analyses of C50 Manufactured Sand Concrete Considering Workability and Compressive Strength

C50 manufactured sand concrete requires good workability and strength, and economic efficiency and carbon emissions also need to be considered. This study incorporates sensitivity and significance analyses to recommend the optimal economic mix composition for C50 manufactured sand concrete. The relationship between cost, workability, and mechanical properties was analyzed by considering the water/binder ratio, sand ratio, fly ash content, and superplasticizer dosage. An optimal composition of C50 manufactured sand concrete was recommended. The cost and carbon emissions were quantified at the optimal composition. The results showed that the water/binder ratio had the most significant impact on the cost and carbon emission, while the sand ratio and superplasticizer dosage had the least. All factors significantly affected its cost and carbon emission. Compared to natural sand concrete, manufactured sand concrete achieved a lower cost but higher carbon emissions. Considering the workability, strength, and cost per cubic meter of concrete, the most economical mix proportion for C50 concrete was recommended with a water/binder ratio of 0.36, a fly ash content of 25%, a sand ratio of 0.42, and a superplasticizer dosage of 1.2%. This composition cost 356 yuan, and carbon emission was 352.6 kg CO2 per cubic meter of concrete. Compared to a composition with a water/binder ratio of 0.34 and fly ash content of 15%, the unit cost can be reduced by 18.4 yuan, and carbon emission can be minimized by 56.6 kg CO2 e/m3. The appropriate water/binder ratio and fly ash content can reduce cost and carbon emissions without compromising the workability, compressive strength, or elastic modulus of C50 concrete. This achieves triple benefits in terms of performance, economy, and the environment when applying C50 manufactured sand concrete.