A framework for multi-objective design of Oyster shell powder–Calcined Clay–Cement (OC3) mortar considering chloride-related durability, cost, and carbon pricing: A case study

Multi-objective optimization has been widely applied to low-carbon mortar mix design, but comparatively few studies have simultaneously incorporated an experimentally measured chloride-related durability indicator and explicit carbon-pricing scenarios into cementitious binder optimization. To address these limitations, this study proposes a multi-objective optimization framework for oyster shell powder–calcined clay–cement (OC³) mortar based on a simplex-centroid design. Mechanical properties, hydration heat, ultrasonic pulse velocity, and surface electrical resistivity (SER) were experimentally measured and fitted as response models. SER was used as a comparative durability indicator, and carbon pricing was incorporated into the total cost function. Results show that adding durability as an objective markedly increases the optimized calcined clay content, accompanied by higher SER. Higher carbon prices further reduce cement content and carbon emissions per unit volume. This framework provides a practical approach for designing durable, low-carbon cementitious materials under carbon pricing scenarios.