damage. On the Great Lakes, floating breakwaters are designed for removal 

 during ice-cover periods to prevent destruction. 



The materials and construction techniques appropriate for the pontoon-type 

 floating breakwaters have been discussed by Miller (1974a, 1974b), Adee 

 (1975b), Araki (1978), and Stormer (1979). These investigators generally 

 concluded that concrete provides the mass and durability necessary for these 

 breakwaters. 



a. Concrete. Richey and Adee's (1975) conclusion that the displaced 

 volume of water is far more important than breakwater shape has another rami- 

 fication regarding the materials used for the construction of the breakwater; 

 i.e., lightweight concrete should not be used. Maintaining the mixing and 

 placing standards is easier with regular concrete which has a long history of 

 successful performance in saltwater. Durability and impermeability, the 

 objectives for concrete used in a floating breakwater, are properties gained 

 with the proper constituents and good workmanship. Chemical attack on con- 

 crete is hastened by sulfates and chlorides in seawater and by carbon dioxide 

 in the air. Salt cells from these chemicals promote galvanic action and 

 corrosion of steel. 



Density and impermeability can be gained with a low water-to-cement ratio, 

 a high cement content, proper compaction and curing (Miller, 1974a). Freezing 

 and spalling resistance is gained from sound, proven aggregates and a dense 

 mix of at least seven sacks of cement per cubic yard, generally, with a mini- 

 mum design strength of 5,000 pounds per square inch. The concrete should be 

 properly cured to the appropriate strength before being placed in the water, 

 to provide adequate resistance to spalling. 



Prestressed concrete should be used in a floating breakwater because of 

 its strength and its resistance to the intrusion of water and chemicals. 

 Prestressed concrete units also easily join together to form a module for 

 installation. Stressed steel is susceptible to fatigue and corrosion from 

 saltwater, so it should be sealed or otherwise protected. All accessories 

 embedded in the concrete pontoon should be noncorrosive materials which will 

 not promote galvanic action; galvanized steel and stainless steel have been 

 used successfully. Records of the use of concrete, which has been used 

 extensively in marina floats, indicate time-dependent deterioration patterns 

 and suggest at least a 20-year lifespan. 



b. Steel . The cyclic loading nature of a floating breakwater requires 

 close scrutiny of the factors necessary to prevent fatigue and brittle frac- 

 ture (Miller, 1974a). The ambient temperature of the structure may not be 

 significant since it is unlikely that the temperature of a floating break- 

 water, even in the most northern latitudes, will drop below -2° Celcius. 

 Design stresses less than 20 percent of the yield stress will probably protect 

 against crack propagation; this level is recommended for the critical areas of 

 connections, anchor attachments, and other components. 



One of the most important considerations for the use of steel in the 

 marine environment is its limited lifespan because of corrosion. Steel should 

 preferably be hot-dip galvanized after all fabrication and welding. Alterna- 

 tively, there are many proprietary coatings on the market, the best of which 

 appears to be a coal-tar epoxy amine type applied over a zinc-rich primer on a 

 sandblasted surface. All stainless steels exhibit some susceptibility to 

 seawater corrosion. Attaching stainless steel to uncoated and unalloyed 

 structure steel may provide cathodic protection. 



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