placed on top and covered by a 3.8-millimeter (.150 mil) layer of high density 

 polyethylene before placing the pile cap. Side and end grain penetration of 

 the preservative completely impregnates the entire pile top to a depth of 

 more than 25.4 millimeters in less than 2 years. 



d. Poles. Prior to World War II, most of the pressure- treated poles 

 used in the United States were treated with American Wood Preservers Associa- 

 tion specification grade 1 coal-tar creosote with a specified distillation 

 residue above 355° Celsius of not more than 20 to 25 percent. Coal-tar 

 creosote treatment may still be the preferred preservative under conditions 

 where waterborne preservatives could leach away or cost may be the con- 

 trolling factor. 



In recent years solutions of pentachlorophenol have attracted attention 

 as substitutes for creosote or for use in mixtures with creosote, and large 

 quantities have been used. Thousands of poles have been treated with 

 pentachlorophenol dissolved in the lighter petroleum oils or with solutions 

 containing various proportions of coal-tar creosote and pentachlorophenol 

 dissolved in a petroleum-oil solvent. These poles have not been in service 

 for sufficient time to determine how the results will compare ultimately 

 with those obtained from creosoted poles. Experimental installations under 

 observation, however, are giving excellent results, so that this preserva- 

 tive may find a wide field of use in the future. 



Most of the poles that have been pressure-treated and on which the best 

 service records are available are southern yellow pine and coastal Douglas- 

 fir. Preservative retention quantities for these and other species are 

 shown in Table 36. The data are taken from Federal Specification TT-W-571J 

 which gives a more complete specification on the treatment of wood poles. 



9. Joining Materials . 



a. Metal Connections . The various members and parts of wooden coastal 

 structures are in nearly all cases joined together by metal. Most common 

 are the bolts, spikes, and driftpins which fasten heavy timbers in structures 

 such as groins, jetties, bulkheads, and piers (Fig. 69) . Another cate- 

 gory includes such items as spike grids and split ring connectors for 

 increasing the shear capacity of bolted joints (Fig. 70), and sheet metal 

 framing anchors for lighter structural framing and miscellaneous hardware 

 such as bearing plates and straps. A third category of metal connection 

 material would include tying items such as rods, wire rope, and chain 

 (Fig. 71). Metal connection material for a timber structure is subject 

 to much the same deteriorating factors in a coastal environment as are 

 metal structures. These are predominantly corrosion and, in some cases, 

 abrasion. They are discussed further in Sections VII and XI. 



In addition to resisting corrosion, the material may also have to 

 resist chafing, or abrasion by drifting sand, floating debris, or moored 

 vessels. This factor should be considered in selecting the anticorrosion 

 coating or system, as discussed in Section XI. Because even the best 

 protective system will have only limited life in a severe marine exposure, 

 a program of periodic inspection and preventive maintenance will probably be 

 needed. 



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