Durability and best corrosion protection for vehicle restraint systems

Vehicle restraint systems make a significant contribution to increasing road safety. An individual component of the systems are the so-called crash barriers made of galvanized steel. Guard rails are omnipresent on motorways and many country roads. Road users must be guided safely and protected from danger. To this end, systems of steel crash barriers are erected along roads to stop, redirect or divert vehicles leaving the roadway.

In addition to the traditional piece-galvanized steel crash barriers according to DIN EN 1461, since 2008 in Germany, for example, crash barriers made of "strip galvanized" steel have also been permitted.
The German Federal Ministry of Transport, Building and Urban Affairs (BMVBS) considers the requirements for the A- and B-bar (components no. 1.00 and 2.00) to be fulfilled with regard to safety, durability and aesthetics. There are no reservations against their use on German federal roads. The basis for the release was a long-term field test under the direction and supervision of the Federal Highway Research Institute (BAST) and the Research Association for Steel Application e.V. (FOSTA). Authorities and institutions in other European countries also assess the advantages of this technological alternative as very positive.

Atmospheric corrosion is mainly influenced by the content of sulphur dioxide in the air in combination with humidity. Furthermore, the durability in outdoor applications is directly proportional to the thickness of the zinc coating on the respective components.
Fortunately, the air quality in Europe has improved massively over the last decades. As a rule, effective long-term corrosion protection is now also achieved with economically thinner zinc coatings. Conventional coatings on crash barriers of up to 70 µm are being replaced by 42 µm thinner coatings. This enables the economical use of the precious raw material zinc, a precious metal that is only available in limited quantities on our planet. The starting material for this new generation of components for crash barriers is continuous hot-dip coated steel according to DIN EN 10346. The continuous strip galvanizing process can be precisely controlled and monitored. This ensures constant zinc layer thicknesses and a homogeneous surface quality over the entire strip length.

The strip galvanized steel strip, e.g. 3 mm thick, is brought into the desired shape on roll forming lines, punched and trimmed. The excellent zinc adhesion to the steel surface allows very tight bending radii. The very ductile zinc layer does not burst open during forming, corrosion protection is also ensured at the bending shoulders. The zinc layer is therefore very resistant to robust mechanical loads during transport, during installation, in contact with vehicles or in the event of stone chipping. Tie bars made of strip galvanized material are free of injurious zinc plumes, pimples and thickenings. They are therefore also very easy to install.

The corrosion on the exposed steel core on the outer edges and the punched holes of the finished tie bars is insignificant. Even after 16 years, field observations in Germany show no signs of relevant corrosion on the punched and cut edges. In fact, this is negligible. Widenings at the screw through holes or rust lugs on the longitudinal edges could not be detected. Structural integrity and optical aesthetics of the components are thus ensured. This finding is explained by an electro-chemical mechanism of action in which the less noble metal zinc is dissolved as a "sacrificial anode". In steel crash barriers, this effect is favoured by the particularly favourable ratio of galvanized surface area to cut edge area.

Strip-galvanized vehicle restraint systems convince through economic production, durability and economical use of resources. The total costs of a vehicle restraint system with bars made of pre-galvanized sheet metal are significantly lower than those of other solutions.