Marine bioreceptivity among green concretes

Coastal population growth and the effects of climate change has led to extensive shoreline development and armouring. In response to the adverse effects of this artificialisation on natural habitats, eco-engineering is increasingly being applied to enhance marine biodiversity. Most 'hard' eco-engineering efforts utilise concrete, but the substantial environmental impact of traditional concrete made with ordinary Portland cement (OPC), such as its huge carbon footprint, may negate the ecological benefits they provide. Incorporating ‘green' concretes into eco-engineering designs should lower this environmental cost as they have less energy intensive production processes and high life-cycle sustainability. However, little is known regrading their ability to act as substrates that can support marine life. Hence, we investigated the marine bioreceptivity of six different green concretes and one regular OPC-based concrete cast into tiles with smooth or rough surface textures. To determine their engineering properties, the concretes were also subjected to compressive strength and ultrasonic pulse velocity tests. We found no significant differences for algal species richness or biomass between green and regular concretes, but there were significant differences in algal percentage cover during the 23-week deployment. Furthermore, rough tiles encouraged faster initial colonisation of green algae and had significantly more red/brown algal biomass than smooth tiles at the end of the study. While the green concretes varied in strength and durability, all were intact at the end of the experiment. We conclude that green concrete has the capacity to support diverse algal communities and is a promising alternative to regular concrete for marine applications.