XII. SUMMARY 



1 . General . 



This section summarizes the principal properties and uses of materials in 

 coastal structures, beach protection devices, and erosion control. Generally 

 more than one material is used in a single coastal structure and compat- 

 ibility and effectiveness of the materials working together must be con- 

 sidered in each case. The selection of materials for a specific coastal 

 structure may require consideration of the cost of labor and availability in 

 addition to the physical properties of the materials. Such considerations 

 influence the design of structures when more than one material can be em- 

 ployed to perform the same job. By considering the properties of materials 

 and their past performance experience, the coastal engineer may select the 

 proper material to achieve his design objective. Material uses are generally 

 considered first for their structural properties and then their durability in 

 coastal structures. In addition to the detailed information given in the 

 preceding sections, the general summary that follows may assist in the 

 selection of materials. 



Most, if not all, of the common construction materials have been used 

 separately or in combinations of two or more in the creation of coastal 

 structures. For example, breakwaters, both detached and shore- connected, are 

 commonly constructed of earth and stone and in many instances capped with 

 concrete armor units. To the commonly used earth and stone, steel and 

 concrete sheet piles have been added from time to time for special functions. 

 Also, asphalt has been used many times as an earth and rock binder for 

 capping such structures and holding the basic materials in place. Bulkheads 

 and retaining walls have been constructed of stone, sheet piles made of 

 concrete or steel, mass concrete, and wood. Groins and jetties have been 

 built of these materials as well. 



Marine and harbor structures of more complex design usually require the 

 use of a variety of materials in construction, the selection based not only 

 on their physical properties but their availability at the site and ease of 

 installation as well as economy of construction. When temporary structures 

 are called for, recycled materials such as broken or crushed concrete, 

 crushed asphalt concrete, blocks and salvaged or scrap metals (such as ships, 

 barges, and railroad cars) have been used. The recent development of a large 

 variety of synthetic materials has resulted in the production of improved 

 coating systems and synthetic films for filter cloths as well as foams for 

 improved buoyancy. The synthetic rubbers are used as energy absorbers in 

 fender piles, bumpers and other protective devices. 



Many materials, when used in coastal structures, require special treat- 

 ment. Wood, for example, will have a substantially improved service life 

 when properly pretreated with creosote and other preservatives. Metals, and 

 more specifically steel, will require protective coatings or cathodic protec- 

 tion (usually both), to be durable in the coastal environment. 



2. Materials . 



a. Stone . 



(1) Properties. Stone refers to individual blocks, masses, or 

 fragments that have been broken or quarried from bedrock exposures,' or are 



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