Splash reinforcement

In principle, stainless-steel reinforcement can be a viable solution for preventing corrosion in a large number of applications. The chloride threshold is much higher than the chloride content that is normally found in the vicinity of the steel even in structures exposed to marine environment or de-icing salts. There is no objection to using stainless steel only where its improved protection is necessary, combined with normal steel at other areas. Hence, stainless-steel bars can be used in the more vulnerable parts of structures exposed to chloride environments, such as joints of bridges or the splash zone of marine structures. Similarly, they can be used when the thickness of the concrete cover has to be reduced, such as in slender elements. 

Jetties are individual or multiple piles interconnected together to form a structure in the seabed and support a deck. The piles of a jetty usually have half of their length in the seabed and the rest in the high tide and splash zones up to the jetty deck. They are often concrete structures reinforced with steel. Cathodic protection using sacrificial zinc or aluminum anodes is installed after the completion of the jetty. With a deepwater jetty the suspension of more than a single anode or placing of alternate anodes at different levels is necessary. A few and larger anodes are necessary while impressed current method is employed. An... 

Thermal sprayed zinc - Zinc is flame or electric arc sprayed onto the concrete surface and a direct connection made to the reinforcement. It can be used as sprayed on marine splash or tidal applications. In drier locations a humectant solution of hygroscopic salts can be applied. Over 50,000 m has been applied, mainly in Florida. 

In steel-reinforced constmctions the chloride ions present in seawater migrate towards the reinforcement, and may cause its corrosion. Rebar corrosion develops most rapidly in the splash zone, owing to a sufficient oxygen supply, high chloride penetration, and the presence of appropriate amounts of water (Sakoda et al, 1992). 

Soft caps of plastic or leather give protection against chemical splashes, especially when working with overhead pipes, tanks, heat exchangers, and other equipment which may leak. Reinforced hats of metal, laminated plastics, or other materials resistant to impact from falling objects should be worn when overhead work is performed (a properly fitting hat gives maximum protection). 

Severe corrosion of reinforced concrete bridge substructures in the splash zone in Florida coastal condition. has led to work on systems for use in those conditions only by Florida DoT. Several clamp on systems have been on trial including conductive rubber mats with zinc metal and wood or recycled plastic clamps with zinc or titanium mesh. The sea vater ensures a good electrical (ionic) connection to the concrete. The systems work from low tide level, or below, up to the top of the splash zone. Some have been in operation for several years. A system using tape and plates to secure the titanium mesh anode has also been experimented with in Australia, along with a scre v on plate (Figure 6.17). 

This chapter covers information applicable to zinc corrosion behavior in general. Chapter 2 covers corrosion in the atmosphere—which is the most important group of environments in which zinc is used. Attack is usually approximately linear with time, but often with some reduction of rate as protective films form. Many results are available, and tables have been prepared for the guidance of designers. Water corrosion follows in Chapter 3, with distinctions between hard and soft tap water (hot and cold), temperate and tropical seawater, and tidal and splash zones. Buried structures—together with a section on earth reinforcement—follow in Chapter 4, and conditions appropriate for zinc sacrificial anodes are included in both Chapters 3 and 4. 

Another geometry for laboratory specimens is a concrete cylinder with an embedded reinforcing bar known as a lollipop specimen. These specimens can be used to simulate marine piles, and frequently are partially immersed to represent the splash tidal zone area [9]. Concrete mixtures... 

Waterfront structures are exposed to a variety of marine environments. The resistance of materials to each of these environments may vary considerably, as weU as appHcabil-ity of various forms of corrosion control in mitigating the anticipated corrosion. The waterfront environment can be divided into five exposure zones sediment, immersion, intertidal, splash/spray, and atmospheric. In most cases, a single type of material will be used for the sediment, immersion, and intertidal zones. In some cases another material may be used for the splash and spray and atmospheric zones of the structure. An example of this would be the use of a reinforced concrete deck over steel pilings. Due to differences in corrosion activity between these zones, the corrosion performance of many materials is substantially different when exposed to two or more of these zones. Figure 1, taken from Ref 4, shows the result of a classical experiment where the corrosion of a continuous strip of... 

Above the splash and spray zone, the marine atmospheric environment is characterized by the climatic conditions such as temperature and relative humidity, but is still usually contaminated by salt. Protection of steel in the marine atmosphere zone is primarily through protective coatings. Cathodic protection can be used to protect reinforcing steel in atmospherically exposed concrete. 

Cathodic protection is used widely for the protection of submerged steel in waterfront structures. It also can provide considerable benefit in the intertidal zone and can even reduce the usually high corrosion rate experienced at the boundary between the intertidal zone and the splash and spray zone. Cathodic protection also is used to prevent corrosion of the soil side of steel in marine structures such as sheet steel bulkheads. Cathodic protection also is effective in the control of the corrosion of reinforcing steel in concrete in all exposure zones in waterfiont structures. Particularly for impressed current systems, it is important to select materials for the cathodic protection system components such as rectifiers and junction boxes with consideration of the environment to which they will be exposed. When considering cathodic protection, periodic inspection and maintenance is required for proper system operation. The costs for inspection and maintenance must be considered in the overall cost of cathodic protection. While there are no specific standards for cathodic protection of piers and docks, information in NACE RP0176 (Corrosion Control of Fixed Offshore Platforms Associated with Petroleum Production) and NACE RP-0187 (Design Considerations for Corrosion Control of Reinforcing Steel in Concrete) contain information that is applicable to marine piers and docks. 

Glass reinforced PA is used to protect brake discs, in the form of stone and splash shields. More significantly, both PA and reinforced PBT have been used for the housings of brake servo mechanisms. Small quantities of more exotic plastics are used in sophisticated ABS systems e.g., injection mouldable fluoropolymers for brake pad sensor housings, and PEEK for carbon brush holders. 

Expanded zinc mesh in a glass-reinforced plastic permanent form filled with a proprietary cementitious grout, usually applied to marine exposed piles in the splash and tidal zone. 

Corrosion Proporlios. Marine corrosion of silicon carbide/aluminum composites is much less severe than that observed on graphite/aluminum MMCs. Discontinuous silicon carbide/aluminum MMCs, however, are susceptible to localized corrosion. Mild-to-moderate pitting has been reported on SiC whisker- and particulate-reinforced composites containiirg 6061 and 5000 series aluminum matrices exposed for a maximum of 42 months in splash/spray and marine atmospheric environments. The d ree of corrosion present on the composites is slightly accelerated compared to that on unreinforced alutrtittum alloys. 

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