Bridges impressed-current cathodic protection

This is probably the most widely used and robust of anodes when properly applied. It accounts for about 50% of the half to one million square metres of impressed current cathodic protection applied worldwide. It is widely used on bridge decks, marine substructures and in any a ressive environment. 

In the United States trials of impressed current cathodic protection have been conducted on pre-tensioned structures (Bennett and Schue, 1998). Many pre-tensioned bridge piles have been cathodically protected in Florida using galvanic anodes. This is unlikely to cause overprotection and hydrogen evolution. 

The most coherent set of comparative data was developed by the SHRP research on repair methods (Gannon et al., 1993). A series of field rehabilitation projects on US bridges was investigated and the data presented in a series of graphs and polynomial eqnations. In the United Kingdom a web-based model for evaluation of structures, selection of repair options and comparative life-cycle costing. The model is available for use at http //projects.bre.co.uk/rebarcorrosioncost/. This includes a comprehensive set of cost tables for galvanic and impressed current cathodic protection,... 

In North America the market for impressed current cathodic protection of bridge decks has diminished (Russell, 2004). High-performance concrete overlays, full and partial deck replacement are preferred due to the cost of maintenance. 

Field tests in the Florida Keys showed that the anodes retained physical integrity for at least 4.5 years. Laboratory test indicated that concrete resistivity does not represent a main limiting factor in performance of such anodes and that periodic water contact (as encountered in the splash/evaporation zone of marine bridge substructures) is actually necessary for long-term anode performance. This low-cost method is a competitive alternative to impressed current cathodic protection systems and a significant improvement over gunite repairs. SHRP-S-405, 10... 

To illustrate randomized block designs, consider the following example an experiment is conducted to test the effectiveness of two humectants (wetting agents) on the operation of impressed current cathodic protection systems on reinforced concrete bridges. There are 120 reinforced... 

J2 Corrosion of steel reinforcing ban (reban) in a concrete bridge head, (a) The corrosion cell which arises due to water penetration and chloride pick-up from the concrete or from deicing salts, (b) The expansive corrosion products may cause cracking of the concrete. Tn severe cases, delamination results, (c) Impressed current, cathodic protection may be applied, (d) A flexible anode mesh may be installed (which is then covered with a concrete overlay)i Power usage is < 10 Wm" of the concrete surface. (Courtesy Raychem Ltd.)... 

Today loading piers are mostly cathodically protected with impressed current. At moorings for tankers, cathodic protection rectifiers are installed on extinguisher bridges as far as possible from the hazardous area. Otherwise, they must be of an explosion-proof type. 

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.)... 

The system was straightforward. One of the popular impressed current pipeline cathodic protection anodes of that time was made of a corrosion resistant silicon iron, surrounded by a carbon cokebreeze backfill. A well was dug near the pipeline, the anode put in surrounded by the backfill and the system connected to a DC power supply, with the negative terminal connected to the pipeline to make a cathodic protection system. Richard Stratfull look pancake silicon iron anodes, fixed them on a bridge deck and applied a carbon cokebreeze asphalt overlay (Stratfull, 1974). The systems installed in 1973 and 1974 were reviewed in 1989 and were still working (Broomfield and Tinnea, 1992),... 

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