Multi-criteria optimisation of the aggregate skeleton for valorising marine dredged sediments and crustacean waste in concrete

To maximise the use of alternative materials in concrete, this study proposes and validates an optimisation framework for the distribution modulus (q) of the modified Andreasen and Andersen model. The targeted application is the design of a mix for articulated concrete blocks for coastal protection, with maximum replacements of sand by marine dredged sediments (MDS) and cement by crustacean waste (CW). The proposed optimisation approach determines an aggregate grading that maximises the incorporation of alternative aggregates while maintaining or improving the slump of concrete. This method adjusts aggregate proportions by considering two main variables: the sediment-to-sand ratio (0–0.7) and the distribution modulus q (0.2–0.5). Iterative algorithms were developed to identify optimal granular combinations based on five theoretical criteria: (1) maximising sediment content, (2) maximising packing density, (3) targeting a sand-to-total aggregate ratio of 0.45, (4) maximising the paste-to-void ratio, and (5) maximising excess paste thickness. Compared to mixtures with simple sand replacement, optimised mixes with 40 % MDS exhibited a 37 % increase in slump and a 10 % increase in 28-day compressive strength. The 28-day compressive strength was further enhanced by partially replacing cement with 15 % CW. The combined use of both marine by-products produced concrete with equivalent properties, a 40 % reduction in sand, and a 15 % reduction in cement, corresponding to a 14 % lower specific carbon footprint and a 15 % cost saving, advantages particularly relevant for remote or island regions. The proposed method provides a systematic and efficient approach, superior to traditional trial-and-error mix design, for developing sustainable concretes using low-value marine by-products.