In this work the performance of mussel shell as aggregate in plain concrete has been studied. The mussel shell used came from the cannery industry, which produces more than 1 million tonnes of shell by-product a year worldwide. The mussel shell has been heat-treated at 135 degrees C for 30 min and then crushed and sieved into sand and gravel. The new aggregates have been studied by X-ray diffraction (XRD), TGA and SEM microscopy. Then two different conventional concretes were designed, a non-structural concrete (NSC) and a plain structural concrete (SC). In both of them the natural aggregates (sand, gravel, and both sand and gravel) were replaced with mussel shell aggregates at different percentages. All concretes were characterized in fresh and hardened states (microstructure, workable life progression, workability, compressive and splitting strength, longitudinal modulus of elasticity, weight loss and water permeability). The results lead to establishing that with this treatment, mussel shell replacement should be limited to 25% of fine or coarse aggregates, or 12.5% of both fine and coarse aggregates. With these percentages the NSC and the SC will display a correct behaviour. (C) 2016 Elsevier Ltd. All rights reserved.