In order to reduce environmental impact of construction sector, by-products from other industries must replace classical raw materials in concrete. In parallel, seashell production in the word represents approximately 17 million tons [1] and their shell represent a calcareous resource that can be valorised. Previous researches have shown that the use of seashell co-products as aggregates in concrete can lead to modifications of thermal and transfer behaviours of concrete (thermal conductivity and capacity, chloride diffusion, air permeability) [2]. In order to limit the number of experimental tests, it is interesting to have models to be able to understand the impact of seashell properties on concrete behaviour including long-term behaviour and optimize the formulations. This study aims at providing models to understand thermal and transfers behaviour of concrete incorporating sea-shell by-products. Input parameters were measured on oyster shell aggregates. First modelling was carried out using the Mori-Tanaka homogenisation scheme that is generally used to model bio-based thermal behaviour [3,4]. In a second time, to consider the potential impact of particular shape of seashell aggregates, concrete samples were scanned by µ-tomography, images were segmented in order to get a mesh with this realistic geometry. Then, thermal and transfer behaviour of concrete was simulated using finite element methods. Results show the influence of seashell aggregates shape and properties on concrete behaviour. The models developed in this study could be used in order to simulate behaviour of concrete using other types of seashells providing that input parameters are measured. REFERENCES [1] FAO, The State of World Fisheries and Aquaculture 2020. FAO, 2020. [2] K. H. Mo and al. Recycling of seashell waste in concrete: A review. Construction and Building Materials, vol. 162, p. 751‑764, févr. 2018 [3] G. Huang and al. A multiscale homogenization model on thermal conductivity of bio-based building composite considering anisotropy, imperfect interface and moisture. Construction and Building Materials, vol. 377, p. 131156, mai 2023 [4] H. Beddaa and al. Experimental investigation and micromechanical modeling of mechanical and durability properties of concrete based on shells from sediments. Cement and Concrete Composites, vol. 133, p. 104684, oct. 2022