Retaining walls, tunnels and bridges made of reinforced concrete characterise the Swiss cityscape and infrastructure. However, many of these structures are already several decades old – and chemical changes in the concrete affect the steel used. If the reinforcing steel begins to rust, the structure loses stability. The damage is particularly problematic in inaccessible places where conventional testing methods fail.
Electrochemical measurements as a new solution
Until now, engineers have had to break open parts of the concrete to check for corrosion damage. A time-consuming and often inadequate procedure. Talpa has developed a new method that works via drainage pipes. A special probe is inserted into the pipe and uses electrochemical signals to measure the likelihood of corrosion in the surrounding reinforced concrete.
“This has never been done before,” explains Lukas Bircher, one of the developers. “Previously, you had to remove entire concrete surfaces to find damage and could still easily miss a critical area.” With the new technology, entire sections of wall can now be systematically tested without destruction or costly construction work.
Measurements during operation – without a construction site
The method has already been successfully tested, including on a 200 metre-long retaining wall in Zurich-Höngg. The principle is a probe that is inserted into the drainage pipe and fixed in place with inflatable seals. The system then directs water into the measuring area, creating a conductive connection between the electrodes of the probe and the steel in the concrete. Based on the recorded electrical signals, the team can recognise whether and to what extent corrosion is present.
A new measurement is taken every 25 centimetres to record the condition of the entire section of wall. “This allows us to specifically identify those areas that actually pose a risk,” says Bircher. “This not only saves time, but also high costs for unnecessary interventions.”
50 years after the construction boom – the need for renovation is growing
Many of the reinforced concrete structures affected today date from the boom period between 1960 and 1980. Retaining walls from the 1970s in particular often contain cavities that favour corrosion. Previously, damage had to be identified by means of time-consuming spot checks, with a high risk of overlooking critical areas. The new method offers a comprehensive and reliable analysis for the first time.
From research to start-up Talpa-Inspection
The technology has such great potential that Bircher founds the start-up Talpa-Inspection together with two colleagues. The name “Talpa”, Latin for “mole”, symbolises the innovative way of making deeply hidden damage visible. Supported by an ETH Pioneer Fellowship, the team is further developing the technology and preparing to enter the market.
Future prospects, automation and scaling
The measurement is currently still partly manual, but the team is already working on an automated version. The aim is to make the probe more robust and further accelerate the measurement process. Demand is high. In Switzerland alone, there are over 1,000 kilometres of potentially affected reinforced concrete structures.
“Our method offers a real opportunity to extend the service life of existing structures,” says Bircher. “We hope that it will soon establish itself as a standard procedure for structural diagnostics.”
