available annually throughout the United States. While, as a material, 

 rubber tires are strong and durable, they have almost no salvage value. 

 Hence, they are generally available at very low cost or just for the cost 

 of hauling. Rubber tires have been used for years as fenders on barges, 

 work boats, and docks but it is only since about 1963 that they have been 

 seriously considered as a low cost, and readily available, material for 

 protection structures. 



b. Characteristics . Salvaged rubber tires have a specific gravity of 

 about 1.2. They are tough, flexible, durable and almost inert to chemical 

 reaction in either fresh or salt water. In fact, the critical strength 

 factor of a scrap rubber tire system is not the "tire" but the fastenings 

 and the mooring system. 



c. Uses. 



(1) General . Salvaged rubber tires have been used primarily to 

 form floating breakwaters but they also have potential use for revetments, 

 groins, bottom stabilizers, and fishing reefs. Experiments are underway to 

 use them as an additive to asphalt concrete paving. 



(2) Floating Breakwater . Like all floating breakwater systems, 

 the use of the floating rubber tire system is most successful where the 

 need is to protect a basin area against short-period waves such as in bays, 

 harbors, and lakes. Several different arrangements of tires have been used 

 and model tested but the basic principles are the same. 



(a) Flotation . Flotation is provided either by entrapped air 

 or by the filling of a part of the tire with urethane foam. The air system 

 works only for tires held in a vertical position. A regular schedule of 

 adding air to replace lost air or compensate for added weight due to sea 

 growth or the entrapment of silt must be established. Tires are bundled 

 together in modules of a workable size and weight and then the modules are 

 assembled into a floating breakwater of design length, width, and depth. 

 Other design factors are the density of the tire assembly and the allowable 

 load stresses on the fasteners and the mooring system. 



(b) Fasteners . The scrap-tire assemblies have been secured by 

 steel cable, galvanized iron chain, nylon rope, or (one of the most success- 

 ful) scrap cuttings from conveyor belt material fastened together with nylon 

 bolts, nuts and washers. The floating breakwater is a dynamic system, in 

 constant motion, so it is imperative that an adequate inspection and mainte- 

 nance schedule for these fastners and their hardware be established. Salvaged 

 telephone or power poles may be used as inexpensive spreaders to frame the 

 assemblage of scrap-tire modules. Poles and spreader framework may be 

 specially treated to extend the useful life of fasteners; however, in view of 

 the low-cost aspect of salvage systems generally this expense may not be 

 justified. 



(c) Moorings . Standard mooring systems of steel cable or 

 galvanized iron chain with anchors or anchor blocks are generally used to 

 hold the breakwater units in place. Mooring stresses will depend on wave 

 forces, density of the tire modules, width of the system, and depth of the 



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