Bridges become an infrastructure problem as they get older, as de-icing salt and carbon dioxide gradually destroy the reinforced concrete. A new robot can now check the condition of these structures, even in places that people cannot reach.
We rely on Switzerland’s 3,500 motorway bridges – plus thousands more on cantonal roads – to carry us safely across valleys, streams, rivers and other roads. Most of these bridges have two factors in common: they are essential to Switzerland’s transport infrastructure and they are made of reinforced concrete. This material makes them safe and durable – until the onset of corrosion.
Corrosion jeopardises Swiss infrastructure
Corrosion occurs when chloride invades from de-icing salt and destroys the reinforcing steel inside concrete or when CO2 from the atmosphere lowers the concrete’s normally high pH. The damage becomes worse over time and is often visible only at a very advanced stage. In the long term, this can jeopardise the usability and safety of bridges and other supporting structures made of reinforced concrete. Furthermore, restoring these bridges is very expensive: the greater the damage caused by the corrosion, the more costly the repair work. “In addition, many bridges in Switzerland are already more than 50 years old, which makes corrosion increasingly problematic for Switzerland’s infrastructure,” explains Bernhard Elsener, professor at the Institute for Building Materials at ETH Zurich.
That is why Professor Elsener and a team of researchers developed the technology 25 years ago to identify corrosion at an early stage, attaching an electrode to a wheel and wheeling it across the surface of the reinforced concrete. The sensor measures the electric potential difference in the reinforced concrete – large differences mean that the reinforcement has already started to corrode in those areas. The data is transferred to a computer and then analysed.