What are the main issues of concern, when designing for structures in a marine environment. What will be added to the concrete to account for cholride attack.

To prevent chloride, sulphate and other forms of chemical attacks, high performance concrete mix are often used in harsh marine environment.

Specifying high cement/water ratio will generally produce water-tight concrete with low permeability. I have done a final-year research which suggested that additives like fly ashes in concrete can produce concrete with very low permeability and high cracking resistance, which will help prevent chloride ion penetration.

Obviously specifying a good (adequate) concrete cover is always goin to help, but it doesn't mean the thicker the better because there are always other issues related to thick covers, such as low shrinkage / cracking resistance which is only going to make things worse. Again, fly ashes
are known to produce concrete with low drying shrinkage and high cracking resistance, which are important criterias for concrete subjected to regular drying and wetting cycles.

Epoxy-coating the reinforcements is probably most effective against short-medium term chloride and chemical attacks in harsh marine environment.

Finding a long-term solution is always going to be a challange. Hope that helps.

As above, the main criteria is to reduce voids as capillary formation by reducing the water content, but also to control crack widths and depths. Capillary blocking additives such as Evedure Caltite give effective water tightness and protect against ingress of chemicals. Limiting the design crack widths to 0.2mm with closely spaced reinforcement is also effective.

We used to make breasting dolphins, most piles used were actualy metal pipe jacketed reinforced concrete (in- situ not prefab) ones. Anyway here's a useful article.http://staff.washington.edu/tranf/Ranf_511.pdf

Cheers 4 the info, that report really cleared things up.

P.

High cracking resistance is the key. Normal concrete has a low enough permeability to ensure no corrosion during a structure's design lifespan. It would take thousands of years for water to seep through concrete of 20mm thick.