freezing climate; adequate coverage over reinforcing steel; durable 

 aggregates; and the proper type of portland cement for the exposure conditions 

 (U.S. Army, Corps of Engineers, 1971a, 1971b). 



Experience with the deterioration of concrete in shore structures has 

 provided the following guidelines: 



(a) Additives used to lower the water-cement ratio and reduce the 

 size of air voids cause concrete to be more durable in saltwater. 



(b) Coarse and fine aggregates must be selected carefully to 

 ensure that they achieve the desired even gradation when mixed 

 together. 



(c) Mineral composition of aggregates should be analyzed for 

 possible chemical reaction with the cement and seawater. 



(d) Maintenance of adequate concrete cover over all reinforcing 

 steel during casting is very important. 



(e) Smooth form work with rounded corners improves the durability 

 of concrete structures. 



2. Steel . 



Where steel is exposed to weathering and seawater, allowable working 

 stresses must be reduced to account for corrosion and abrasion. Certain steel 

 chemical formulations are available that offer greater corrosion resistance in 

 the splash zone. Additional protection in and above the tidal range is pro- 

 vided by coatings of concrete, corrosion-resistant metals, or organic and 

 inorganic paints (epoxies, vinyls, phenotics, etc.). 



3. Timber . 



Allowable stresses for timber should be those for timbers that are 

 continuously damp or wet. These working stresses are discussed in U.S. 

 Department of Commerce publications dealing with American lumber standards. 



Experience with the deterioration of timber shore structures (marine use) 

 may be summarized in the following guidelines: 



(a) Untreated timber piles should not be used unless the piles 

 are protected from exposure to marine-borer attack. 



(b) The most effective injected preservative for timber exposed 

 in seawater appears to be creosote oil with a high phenolic content. 

 For piles subject to marine-borer attack, a maximum penetration and 

 retention of creosote and coal-tar solutions is recommended. Where 

 borer infestation is severe, dual treatment with creosote and water- 

 borne salt (another type of preservative) is necessary. The American 

 Wood-Preservers Association recommends the use of standard sizes: 

 C-2 (lumber less than 13 centimeters (5 inches) thick); C-3 (piles); 

 and C-18 (timber and lumber, marine use). 



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