Durability of reinforced concrete in marine environments

26-09-2024 | Posted by Joaquín Martí

Reinforced concrete is widely used in marine environments due to its ability to withstand the harsh conditions present near coastlines and underwater. But its durability in marine environments depends on factors like the quality of the concrete mix, the level of exposure to seawater and marine organisms, the design of the structure, and the maintenance practices.

The general question of durability, including that of concrete structures, has already been treated in two previous posts. In marine environments, the main factors that affect the durability of reinforced concrete structures are:

• Concrete Mix Design: The quality of the concrete mix is crucial for durability. Proper mix design, including the use of suitable cement, aggregates, and admixtures, can enhance the concrete’s resistance to chloride penetration and chemical attacks from seawater.
• Cover Thickness: The concrete cover over the reinforcing steel is essential to protect it from corrosion. A thicker cover helps prevent chloride ions from reaching the steel and initiating corrosion.
• Chloride Exposure: Seawater contains chloride ions, which can penetrate concrete over time and lead to corrosion of the reinforcing steel. The lower the concrete porosity and the chloride content, the lower the risk of corrosion.
• Pre-stressing: Prestressing reduces or eliminates tensile stresses in the concrete, which helps control cracking. Cracks in concrete can provide pathways for substances, such as chloride ions, to penetrate and reach the reinforcing steel.
• Marine Organisms: Marine environments host various organisms that can attach themselves to concrete surfaces, leading to the formation of biofilms and potential deterioration of the concrete.
• Tidal and Wave Action: Structures in the marine environment are subject to cyclic wetting and drying due to tidal and wave action, which can contribute to the deterioration of concrete over time.
• Design and Construction: Proper design and construction techniques, including appropriate concrete cover, reinforcement, and pre-stressing, are essential to ensure the longevity in marine environments.
• Maintenance: Regular inspection and maintenance help to identify any signs of deterioration and apply appropriate repair and protective measures.

To enhance the durability of reinforced concrete in marine environments, engineers can use additional measures such as cathodic protection, epoxy-coated reinforcing steel, or fibre-reinforced polymer (FRP) composites. Overall, when properly designed, constructed, and maintained, reinforced concrete structures exhibit good durability in marine environments.

Principia has been involved in many such structures, but floating structures for wind turbines are a relatively recent and important addition . There are primarily four concepts currently being considered for the support structure, all of them moored to the sea bottom. Perhaps the most common one is a semisubmersible structure with active damping achieved by water pumping

 A second possibility is a spar structure, heavily ballasted at the bottom to maintain its upright position. A third one is a tension-leg platform, where the tension of cables fixed to the sea bottom compensates the buoyancy of the structure. The fourth one is a square barge shape, where water sloshing within the barge frame dampens its movement. Principia has already participated in studies dealing with several of those concepts and is confident there will be many more projects in that area.