84. What are the best materials to use for building a pier? 



Because piers are constructed and used in all geographic climates and 

 because of the variety of marine conditions that piers are exposed to, 

 experts hesitate to recommend a universal "best material" for piers and 

 other marine constructions. 



Piers and harbor and shore constructions are subjected to corrosion, 

 abrasion, marine borers, and fouling. Since World War II, extensive per- 

 formance and service life tests of the basic heavy structural materials- 

 timber, concrete, and steel— have been undertaken in hundreds of loca- 

 tions; on these basic materials an infinite number of paints, adhesive 

 coatings, impregnations, and protective coverings have been tested. 

 There is no structural material that can be guaranteed to withstand the 

 extreme forces and pressures of waves generated by a hurricane or of 

 sea ice driven by wind and current. 



Results of experiments using steel piles for shore protection show 

 the greatest deterioration at the beach surface. The corrosion created 

 by the salt spray, combined with the constant "sanding" movement of 

 the beach, causes this location on the pile to erode 10 times faster than 

 any other. 



In many cases, galvanic protection is given to steel piers. Galvanic 

 corrosion occurs because sea water is a good electrolyte; the system acts 

 on the same principle as a battery. Mill scale and other chemical and 

 physical differences in steel cause it to act as a bimetallic, setting up an 

 anode and a cathode in the electrolyte (sea water). Corrosion protec- 

 tion is afforded by attaching magnesium, aluminum, or zinc oxide bars 

 below the level of mean low water; direct current using scrap steel or 

 graphite anodes can be used to give the same protection. 



Certain marine mollusks and crustaceans cause extensive damage to 

 timber structures in sea water each year. The mollusks as larvae enter 

 the timber through a small hole and grow to full size inside the wood; 

 crustaceans destroy the surface, burrowing very close together and 

 creating a system of interlacing holes that weaken the wood and permit 

 waves and currents to break off the damaged wood and carry it away. 

 Cases are recorded where untreated piles 16 inches in diameter have 

 been severed in 6 months and creosote-treated piles needed replacement 

 in 2 years! Such destruction has been reported in widely different geo- 

 graphic locations— Puerto Rico, Florida, Nevv/foundland, California, New 

 York, and Alaska. Two common methods of pile protection are creo- 

 sote pressure treatment and use of precast concrete jackets. The value 

 of the latter covering is questionable, since marine borers are also known 



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