The study of long-term durability and bio-colonization of concrete in marine environment

The purpose of this paper is to study the long-term durability and bio-colonization of concrete in marine environment. In this work, concrete formulations were developed and optimised by varying the type of cement (CEMII and CEMV) and introducing shellfish by-products (Oyster Shells) into their composition (by substituting 20% by weight of 4/10 aggregates). Four concrete formulations were thus studied. The durability of these materials upon bio-colonization were tested after 90 days, 180 and 360 days of immersion in natural seawater. The monitoring of the photosynthetic activity of biofilms and the biomass on the materials surface showed a better acclimatisation of the microphytobenthos in CEMII 20% Shells concrete than in other concretes despite a lower colonization on this concrete. It was also noticed that the chlorophyll biomass was the highest in concrete CEMV 20% Shells after 360 days. During immersion, the mechanical strengths of CEMII 0% Shells, CEMII 20% Shells and CEMV 20% Shells increased. At long term of immersion, the chloride ions diffusion was more reduced, in natural seawater, for CEMII 0% Shells, CEMII 20% Shells and CEMV 20% Shells concretes than for concrete CEMV 0% Shells. these results lead to the assumption that the accumulation of biofilm plays a role as protective barrier against the action of chloride ions. Finally, it appears that the concrete CEMII 20% Shells is the most suitable concrete mix design for marine infrastructure amongst the tested designs.