Résumé
FOWTs operate in deep waters. A durable concrete cover in the submerged zone is critical in immersed components because it prevents the transport of aggressive ions, and thus protects the reinforcement from corrosion. The aim of this interdisciplinary study is to identify the surface interactions between cementitious materials, biofouling at their surface, and seawater with emphasis on, (i) the influence of the material on the composition and structure of biofilm, and (ii) the influence of biofilm and seawater on mineralogical and chemical changes within cementitious matrix. Mortars and concrete are prepared using two low-CO2 binders incorporating supplementary cementitious materials, CEM III and CEM V, as well as a conventional binder, CEM I. The specimens were submerged at a depth of 27m at SOLA station, Banyuls-sur-mer, France. Biofouling was characterized using Environmental Scanning Electron Microscope (ESEM) and environmental DNA analysis, whilst, microstructure, mineralogical, and chemical changes in cementitious materials were determined using SEM coupled to Energy Dispersive Spectroscopy (SEM-EDS), X-Ray Diffraction (XRD), and Electron Probe Micro Analysis (EPMA) respectively. Our results suggest that irrespective of the binder-type and age, earlyage exposure (after 30- and 90 days) leads to the precipitation of calcium carbonate, mainly in the form of aragonite at seawater/biofilm-concrete interface. EPMA findings on CEM I concrete indicate calcium leaching and Mg-precipitate on the outer layers. After three months, sulfur-rich and chloride-rich zones followed the Mg-rich zone. The microbial diversity in marine biofilms was determined as a function of binder-type, the differences in composition fading over time on concrete surface.