to attack low-grade concrete and soft stone. Certain tropical woods, 

 such as Greenheart found in British Guiana, have a natural resistance 

 to marine borers, but most woods must be protected. 



Concrete structures tend to "grow" in sea water. A case on record 

 cites a 13-foot-diameter concrete cylinder that increased 6 inches in di- 

 ameter and 4 inches in height. In another case, a steel cylinder of 1/4- 

 inch steel plate filled with concrete "grew", causing the plates to 

 rupture. High-silica-cement piles covered or impregnated with asphalt 

 have proven quite satisfactory; an engineering report on piers built with 

 these specifications indicates that they were in excellent condition after 

 10 years of exposure and use. 



Woods Hole Oceanographic Institution 



Marine Fouling and Its Prevention, Annapolis, Maryland, U. S. 



Naval Institute, 1952. 

 Morgan, J. H. 



Cathodic Protection, Its Theory and Practice in the Prevention Of 



Corrosion, Macmiilan Company, 1960. 



102 



