A novel method for the optimal design of low-carbon fly ash hybrid concrete considering carbonation durability: case studies for five cities

초록

Conventional fly ash concrete mix design often neglects carbonation durability, increasing the risk of reinforcement corrosion. This study proposes an optimization-based approach using a genetic algorithm to minimize cementitious carbon emissions while satisfying two critical constraints: 28-day compressive strength >= 30 MPa and 50-year carbonation depth <= 25 mm. The genetic algorithm's main advantage lies in its adaptability to various carbonation exposure conditions. The main contributions of this work include enabling a unified, performance-based, and climate-adaptive mix design strategy for low-carbon fly ash concrete. The method was applied to five cities with different climates: Seoul, Sydney, Beijing, Singapore, and New York. Results indicate that in moderately humid cities (Seoul, Sydney, Beijing), carbonation durability governs the design, requiring increased compressive strengths of 40.18 MPa, 46.14 MPa, and 45.03 MPa, respectively. In more humid environments (Singapore, New York), slower carbonation allows the target strength of 30 MPa while maintaining carbonation durability. Higher required strength increases binder content and CO2 emissions, while lowering the water-to-binder ratio. In all cases, the optimized mixes successfully met both strength and carbonation durability requirements. Additionally, the method highlights how climate conditions can shift the governing factor in mix design.

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