Deck anode systems

Deck anode systems are generally embedded in a concrete overlay or recessed into slots cut in the deck. There are advantages and disadvantage. to both approache." , CK erlays increase the thickness of the deck, which can increase the deadload and reduce clearances. Anodes recessed in slots avoid these problems but they are difficult to cut and must be close together (about 300 mm) for adequate current. spread. 

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 ... 

This anode system is one of the most durable and can be applied in any condition from underground and underwater to dry atmospheric exposure where the change in appearance, profile and dead load is acceptable. It has been widely used on trafficked decks and on snbstrnctures, particularly in marine exposure conditions. 

The first reinforced concrete-impressed current CP system was an experimental system installed on a bridge support beam in 1959 [5]. A more advanced system was subsequently installed on a bridge deck in 1972 [6]. The anode system used in both applications was based on a conventional-impressed current CP system for pipelines, but "spread out" over a bridge deck. CP has since then become one of the few techniques that can be applied to control corrosion on existing structures. 

Rehabilitation is achieved by overlays such as latex-modified concrete, low-slump concrete, high-density concrete, and polymer concrete. They are commonly used for the rehabihtation of bridge decks. This procedure extends the life of a bridge deck by about 15 years. Impressed-current CP systems on bridge decks are now a routine rehabihtation teehnique because of the cooperative research with industry and states in the development of durable anodes, monitoring devices, and installation techniques. Titanium mesh anode, used in conjunction with a concrete overlay to distribute protective current, serves as a durable anode for use in impressed-current CP of reinforced concrete bridge deeks and widely accepted by state and other transportation agencies. 

Anode selection and application have proven to be a challenge in designing CP systems for concrete structures with adequate life. The anode for concrete bridge deck should have the following features ... 

Of all the systems cited above, only the titanium mesh anode and metallized zinc are in extensive use at present. The titanium mesh on bridge decks is durable over long time. The thermal-sprayed zinc is free from debonding problems but suffers from an increase in resistance over time. However, the Oregon DOT has had significant success with thermal-sprayed zinc anode on substructure components. The thermal-sprayed titanium has shown promise as a new anode. 

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. 

One of the first commercial, proprietary anodes for decks was a flexible cable with a conductive plastic round a copper condnctor. The cable was woven across the deck and then a concrete overlay applied. It was also used on substructures with a sprayed concrete overlay. This system was very popular in the 1980s but unfortunately the condnctive plastic started to fail after about five year s of service. This led to attack of the copper and, in some cases, expansion of the plastic which delaminated and spalled the concrete overlay. This system is no longer available. 

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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