Klassificering av vägtunnlars korrosivitetsgrad - Underlag för val av metalliska material och rostskyddssystem

Classification of the corrosivity of road tunnels – Basis for selection of materials and corrosion protection system

An increasing number of large road tunnel systems are being built or planned. The tunnels contain a number of metal components, such as road and traffic signs, light installations, cable racks, sheet steel linings, brackets, fasteners and other fixtures. The components are placed in various parts of the tunnels and exposed to the effects of differing levels of aggressive factors in the environment. Commonly used metallic materials that may be subject to corrosion are steels with rust protective painting, zinc coated steel with or without protective painting, coated or uncoated aluminium sheet and stainless steels. Little consideration is given today in the selection of metallic materials and corrosion protection measures to the fact that the degree of corrosivity in the tunnels will vary. A major reason for this is the lack of a technical basis for classification of the corrosivity. With a classification system specifically for road tunnels the selection of materials and corrosion protection system can be optimised. High-alloy stainless steels are for instance needed locally in certain particularly aggressive parts of the tunnel environment instead of the commonly used stainless steel grades and other less corrosion-resistant materials. By optimising the selection of materials and corrosion protection systems the total cost of maintenance, and also the risk for unexpected damage, will be decreased. The aim of the project is to establish criteria for assessment of the degree of corrosivity in road tunnels and, on the basis of this classification system, to prepare guidelines for the selection of metallic materials and corrosion protection system on construction of road tunnels as well as for the maintenance of existing tunnels. The project will thus provide a system for corrosivity classification of road tunnels, to be used for selection of materials as well as protective measures. The system will also serve as a basis for setting up maintenance programmes for road tunnels. Application of the classification system is expected to result in an increased lifetime for the metal components in the tunnels, and lower repair and maintenance costs. A number of tunnels will be selected to represent different typical road tunnel environments. The exposure sites will be chosen so that a range of geography, climate and traffic intensity factors will be covered. At each exposure site an exposure rack will be installed with test panels from carbon steel, zinc, stainless steel and aluminium. In addition steel and zinc panels with different pretreatments and selected coating systems will be exposed. Double test series will be set up so that intakes of panels can be made after two and four years respectively.