Low, not no maintenance - materials such as weathered steel or composites have special design and maintenance needs
This is an interesting and challenging time for those responsible for maintaining and updating our civil infrastructure. We've always had to keep an eye on the money.
But now we also have to concern ourselves with factors such as sustainability and greatly enhanced health and safety requirements for workforce and public alike. It is no wonder that interest in "low maintenance" options such as weathering steels and advanced composite materials is on the increase.
These alternatives to carbon steel or reinforced concrete appear to offer the prospect of structures that require little or no maintenance. Although they may involve greater cost and carbon to produce, their predicted long life with little intervention has the potential to more than offset this.
In reducing the need for maintenance it is possible to limit the amount of work at height required and the potential impacts of inspection and maintenance on availability of the structure or the roads, railways or watercourses beneath them.
Such approaches are not risk free, however. Weathering steel is capable of delivering very long life. But in order for a stable layer of corrosion product to form, the conditions have to be right. This is totally dependent upon correct design, specification, fabrication and maintenance.
In the UK, where relatively little weathering steel has been used to date, great care has generally been taken to ensure optimum performance.
Unfortunately, there are many examples in other countries where lack of surface preparation, trapping of water and de-icing salts, poor maintenance of deck joints or debonding of the protective oxide layer due to vibration have led to corrosion rates similar to uncoated carbon steel.
It is essential that an increased use of weathering steels is accompanied by greater awareness of design, fabrication and maintenance needs. Designers need to acknowledge that regular inspection is required and provide for safe access – assuming that you can economise by designing out access detailing because you are using low-maintenance materials in reality elevates health and safety risk.
We also have to ensure that those tasked with the inspection of such structures have the tools and skills to properly assess their condition.
This is particularly important as one of the principal visual inspection methods, looking for rust and brown stains, is clearly not appropriate for a material that relies on a layer of rust for its protection.
We face a similar challenge with advanced composite materials such as fibre reinforced polymers (FRP). Techniques have to be developed for their inspection and testing and inspectors need to be trained to use them.
We will be embracing these alternative technologies as they have much to offer. But we must ensure they are employed appropriately by committing to the training and support required. We must also acknowledge that there is no such thing as “maintenance free”.
- Paul Lambert is Mott MacDonald’s materials and corrosion engineering technical director