Mix design optimisation for concrete with alternative binders and aggregates incorporating environmental, mechanical and durability performance

The design of environmentally efficient concretes remains challenging due to the conflicting requirements of reducing embodied carbon while maintaining durability and mechanical performance, particularly when recycled aggregates and supplementary cementitious materials ( SCMs ) are used. This study presents a performance-based optimisation framework that integrates mix design variables, service-life prediction, and life-cycle assessment ( LCA ) to minimise global warming potential ( GWP ) while meeting durability requirements. The framework combines artificial neural networks (trained on 4828 experimental mixes), phenomenological chloride diffusion modelling, and a cradle-to-gate life-cycle assessment, optimised using genetic algorithms to minimise global warming potential and natural aggregate usage while meeting chloride diffusion requirements. Results show that switching from GWP minimisation to natural aggregate conservation requires a reduction in water-to-binder ratio ( w/b ) by 8–30 % and an increase in binder-to-aggregate ratio ( b/a ) by 40–114 %, which consequently raises GWP . Among SCMs , GGBFS achieves up to 48 % lower GWP , followed by silica fume (47 %) and fly ash (35 %). Multi-objective analysis indicated that incorporating recycled aggregate at approximately 30 % balances durability, resource efficiency, and emissions, whereas full replacement significantly increases GWP unless offset by the use of large volumes of SCMs . Service-life modelling revealed that high-diffusivity concretes required up to 58 kg CO 2 − eq / m 2 additional emissions through increased cover depths, while SCM -enhanced mixes consistently achieved target service-lives with minimal cover penalties. By combining material optimisation with performance-based cover design, the framework identifies mix designs that balance durability, environmental efficiency, and resource conservation, supporting long-lasting, low-carbon concrete elements.