Coastal marine ecosystems provide essential benefits and services to humanity, but many are rapidly degrading. Human activities are leading to significant land take along coastlines and to major changes in ecosystems. Ecological engineering tools capable of promoting large-scale restoration of coastal ecosystems are needed today in the face of intensifying climatic stress and human activities. Concrete is one of the materials most commonly used in the construction of coastal and marine infrastructure. Immersed in seawater, concretes are rapidly colonized by microorganisms and macroorganisms. Surface colonization and subsequent biofilm and biofouling formation provide numerous advantages to these organisms and support critical ecological and biogeochemical functions in the changing marine environment. The new challenge of the 21st century is to develop innovative concretes that, in addition to their usual properties, provide improved bioreceptivity in order to enhance marine biodiversity. The aim of this study is to master and clarify the intrinsic parameters that influence the bioreceptivity (biocolonization) of cementitious materials in the marine environment. By coupling biofilm (culture-based methods) and biofouling (image-analysis-based method and wet-/dry-weight biomass measurement) quantification techniques, this study showed that the application of a curing compound to the concrete surface reduced the biocolonization of cementitious materials in seawater, whereas green formwork oil had the opposite effect. This study also found that certain surface conditions (faceted and patterned surface, rough surface) promote the bacterial and macroorganism colonization of cementitious materials. Among the parameters examined, surface roughness proved to be the factor that promotes biocolonization most effectively. These results could be taken up in future recommendations to enable engineers to eco-design more eco-friendly marine infrastructure and develop green-engineering projects.

The French National Program RECYBETON aims to move the scientific boundaries relative to the use of recycled aggregates into concrete. The objective of this study is to qualify and quantify the hydric transfers between the recycled coarse aggregates and cement paste at early age. Concretes for building and civil engineering structures are tested. The concrete formulation of the reference (natural aggregates) and recycled concretes has been calculated by RECYBETON and specific initial slumps and 28 days compressive strengths are targeted. An original test is proposed to separate the fully and partially saturated recycled aggregates from the fresh cement paste. In our test conditions, absorption occurs quickly independent of the initial saturation degree of the recycled aggregates. The paste volume and water content are stable at the end of mixing. To exacerbate desorption phenomena and to provoke early age cracking, a severe drying is applied on fresh concretes. Water desorption of recycled aggregates is observed. A strong relationship between the time of initiation of the cracking and the total water content is established for recycled concretes: the time is an increasing function of the total water content. Recycled concretes tend to have wider cracks opening compared to reference concretes.

Marine sediment disposal is an important economic and environmental issue worldwide. In order to minimize these discharges and optimize resources through a circular economy approach, this study discusses the potential use of fine marine sediments without treatments as a sand substitute in the marine concrete class (XS2, C30/37). The Dreux-Gorisse method was applied to find the concrete formulation containing 10, 20, 30, 40 and 50% sediment by weight. The results show that an XS2 concrete C30/37 with a water to binder ratio of 0.55 could be designed with 10% of sediment replacement content without significantly affecting the concrete properties. However, the optimization of concrete mix design shows that marine concrete (XS2, C30/37) could be designed with 30% of sediment replacement content without significantly affecting the potential durability and the estimated lifetime of the concrete structure.

The disposal of marine sediments poses a significant economic and environmental challenge on a global scale. To address this issue and promote resource optimization within a circular-economy paradigm, this research investigates the viability of incorporating untreated fine marine sediments as a partial replacement for sand in self-compacting concrete (SCC) designed especially for application in marine environments (an exposure class of XS2 and a resistance class of C30/37 according to standard NF EN 206). The concretes mis-design incorporating 30% by weight of sediment as a sand substitute was initially designed with the modified Dreux–Gorisse method. The findings indicate that it is feasible to design an SCC suitable for marine environments, incorporating 30% sediment replacement content and without significantly compromising concrete properties, durability, or the estimated lifespan of the formulated concretes. The integration of marine sediment as a sand substitute into the SCC mix design reduces the amount of binder and limestone filler without compromising the paste volume. This results in a significant saving of natural sand resources and a reduction in CO₂ emissions for SCC made with marine sediment.

The incorporation of recycled glass fiber reinforced polymer (rGFRP) in cementitious materials is an interesting recycling and valorization method. However, this incorporation generally results in a significant loss of workability, often compensated by an adjustment of the water to cement ratio, which can affect mechanical performance, particularly compressive strength. The aim of this paper is to examine the effect of different size fractions of rGFRP (0.063 mm, 0.16 mm, 0.63 mm, 1.25 mm and 2 mm) on the mechanical strengths of cement mortars with a mixing method that is likely to maintain the workability of the mix without adjusting the water to cement ratio. For this, a substitution rate of 10% (in volume of sand by rGFRP), supposed to induce workability loss, is chosen. A pre-mixing of rGFRP with water before adding cement and sand is performed and allows for the workability to be maintained without increasing the water content. The results show that compressive and flexural strengths are almost maintained compared with reference mortar for two rGFRP size fractions (2 mm and 0/2 mm). For the 2 mm fraction, a slight improvement (3%) in flexural strength after 7 months of curing and a 5% reduction in compressive strength are observed. After 7 months of curing, fibers or clusters of rGFRP are still observed, although they are not alkali-resistant.