1.1.1                            MARINE FOUNDATIONS

Corrosion protection of marine foundations should be provided in accordance with acceptable standards or codes of practice for design of maritime structures, such as “Port Works Design Manual Part 1” published by Civil Engineering and Development Department. The following should be considered as general guidelines:

(1)       Concrete

Concrete should be of high density and low permeability. It should not be inferior to grade C45 and the water/cement ratio should not exceed 0.38. Condensed silica fume should be added to reduce the permeability of concrete. The cementitious content should be 380 to 450 kg/m³, of which the dry mass of condensed silica fume should be within 5 to 10% range by mass of the cementitious content.

Nominal concrete cover to all reinforcement in all  exposure zone should  be 75 mm.

Crack widths of concrete within tidal and splash zone should not exceed

0.1 mm under typical average long term loading conditions, which may be increased by a factor of 1.25 for flexural crack width design and control purpose.

Correct use of pulverized fuel ash in the concrete mix may increase resistance of concrete against sulphate attack.

(2)       Steel

All structural steelwork above seabed level, whether fully immersed, within the tidal or splash zones, or generally above the splash zone, should be fully protected against corrosion for the design working life of the structure. Below seabed level, an allowance for corrosion loss of 0.05 mm per year on the outside face of steel is considered reasonable if no corrosion protection is carried out within this zone.

Stainless steel for use in marine environment should be of a grade which is absolutely free of any chloride. Common grade of stainless steel with the presence of chloride should not be used for marine works.

Steel embedded in concrete and steel in seawater in the same foundation should be isolated since the former is cathodic relative to the latter.