Bridges corrosion control

The effort to implement bridge corrosion control maintenance practices, which achieve regulatory requirements and cost efficiency, cannot be successful without the development of reliable task-based cost data for bridge painting tasks. These data depend on many factors such as local labor costs and structural factors such as accessibility to contractor costing rules. 

Dust control is a major problem in corrosion control by silicone polymers. Dust particles which may bridge, or meerly lay upon conductors will absorb moisture diffusing through the silicone and result in a localized site of corrosion. We found this to be the case in a number of our early saunples. Following the results of this study, all of our encapsulated assemblies will be cleaned and encapsulated in a clean room which is serviced by HEPA filters. 

The methods utilized for corrosion control on bridges are specific to the type of bridge construction and whether its intended use is for new construction or main-tenance/rehabilitation of existing structures. The present discussion is focused on the... 

In the present discussion, reinforced concrete and prestressed concrete corrosion control methods are combined. Although prestressed concrete bridges have special concerns such as anchorage in both posttensioned and pretensioned structures and ducts for post-tensioned structures, the general corrosion control methods are applicable to both prestressed and conventional reinforced bridges. 

Salt-induced reinforcing steel corrosion in concrete bridges is a serious problem and an economic burden. Although the positive effect of corrosion protection measures can be seen on individual cases, there are many bridges (thousands) without corrosion control. 

It is useful to note that even the latest corrosion control methods are not likely to prevent all corrosion for the fife of the bridge structure. Therefore, there is a need for repair/rehabilitation of bridge stmctures, and the mitigation of existing corrosion will draw the attention of bridge engineers for years to come. 

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 ... 

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 ... 

Cathodic protection is a proven corrosion control method for protection of underground and undersea metallic structures, such as oil and gas pipelines, cables, utility lines and structural foundations. Cathodic protection is now widely applied in the protection of oil drilling platforms, dockyards, jetties, ships, submarines, condenser tubes in heat exchangers, bridges and decks, civil and military aircraft and ground transportation systems. 

Cathodic protection is by far the most versatile method of corrosion control, since it is applicable to any electrically continuous structure within a suitable electrolyte. Inasmuch as the steel embedded in concrete, and not the concrete itself, requires the protection from metallic corrosion, damp concrete serves as a suitable electrolyte, and even structures exposed to the atmosphere, such as bridge decks, can be protected cathodically. 

Exposure of the samples to a controlled moist atmosphere containing sulphur dioxide, as recommended in BS 1615 1972, Method H, is an example of a test bridging the gap between sealing tests and accelerated corrosion tests. After exposure for 24 h at 25 2°C, poorly sealed films show a persistent heavy white bloom, while good sealing produces at the most a slight superficial bloom. 

The slope is indicative of the type of release mechanism. A slope of 0.5 indicates a diffusion-controlled release a slope of 1.0 indicates that a corrosion-related mechanism is operable.The diffusion release mechanism is characterized by surface adsorption, ion exchange, and migration. Chemical corrosion, or alteration of the silicate lattice, is characterized by hydroxyl attack on silicon or by hydrogen attack on bridging oxygens. 

Since steel is the main structural material for bridges, buildings, and automobiles, controlling its corrosion is extremely important. To do so, we must understand the corrosion mechanism. Instead of being a direct oxidation process, as we might expect, the corrosion of iron is an electrochemical reaction, as illustrated in Fig. 11.17. 

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