Bridges sacrificial anode

Nernst equation 778 overvoltage 794 sacrificial anode 792 salt bridge 766 standard cell potential... 

Sacrificial anode CP systems have been used for the corrosion control of bridge decks as long as impressed-current anode systems for corrosion control of bridge decks. Two of the earliest field trials (1977) for sacrificial anode systems were the following ... 

Both systems performed well for 14 years prior to removal because of failure of the asphalt overlay and the necessity of widening the structure. Although the sacrificial anode CP systems perform well, the majority of the CP systems on bridge decks are impressed-current systems. 

Because of the relatively high resistivity of atmospherically exposed concrete substructures, most anodes utilize impressed current to achieve the necessary driving voltages to supply the current required for corrosion control. However, an exception to this is the use of sacrificial zinc anodes for CP of coastal bridges in Florida, which have a relatively low concrete resistance. However, studies continue to examine the use of sacrificial anodes because of the benefit of its low maintenance compared to impressed-current CP systems. Two of these studies are the following ... 

There are several methods that can be used to control corrosion of steel reinforcements in concrete. First, the design of the structure should provide for drainage of salt-containing waters away from the reinforced concrete. Second, concrete of adequate thickness, high quality, and low permeability should be specified to protect the reinforcements from the environment. Third, chloride content of the concrete mix should be kept to a minimum. For further protection, the steel reinforcements can be epoxy-coated. In many parts of North America, steel reinforcements used in bridge decks are now epoxy-coated as a standard construction procedure. Cathodic protection is also being used, both with impressed current anodes and with sacrificial anodes [61]. (See Chapter 13.)... 

Sacrificial anodes can be used in continuously w etted environments. These systems are not yet fully understood but they seem to be. successful as arc sprayed zinc on marine bridge substructures. They need less maintenance than the impressed current systems. One problem with the zinc system is the environmental impact during. praying. If enclo.>iure is required during spraying, the costs can be very... 

Definitions. Define briefly (a) difference of potential, (b) electromotive force, (c) salt bridge, (d) anode, (e) positive electrode, (f) reference half-cell, (g) standard electrode potential, (h) decomposition potential, (i) overvoltage, (j) sacrificial anode. 

Use of a sacriflcial anode, a metal more easily oxidized than the one to be protected, attached to it. Used for large stmctures such as bridges. A disadvantage is that sacrificial anodes must be replaced when completely oxidized (think of an undergroimd pipeline). 

---