Modern civilisation is built on concrete and steel. Put the two together, though, and you can generate a problem.
Reinforcing concrete with steel rods called rebars is the basis of modern construction.
But because water gets in through tiny cracks, the rebars rust. This causes them to expand, widening the cracks and weakening the concrete.
Hence such structures require constant attention and often have design lives of only 60-100 years.
That is pitiful compared with, say, the concrete dome of the Pantheon in Rome—which was completed in 125ad and still stands.
Various ways of delaying or preventing concrete cancer, as this corrosion is known colloquially, have been tried.
These include recipes for concrete that is less permeable to water,
and rebars made from rust-resistant materials such as stainless steel or composites.
Such approaches work, but they can be expensive. This may be about to change.
Next year, if all goes well, a pair of footbridges intended to be cancer-proof will open in Geelong, a town 75km south-west of Melbourne, Australia.
These bridges, which will act as prototypes for more than 150 others planned for the expanding city,
will be constructed using a novel approach that combines glass-fibre and carbon-fibre rebars.
They will, though, cost about the same as equivalent conventional bridges.
The new design is the brainchild of a joint team of researchers from Deakin, a local university, and Austeng, the firm contracted to build the bridges.
This team began with commercially available rebars made from carbon-fibre composite.
Although these are as strong as steel ones, they are expensive.
They are, therefore, most often used in specialist structures such as buildings to house MRI hospital scanners,
where electromagnetic interference from metal can cause problems.