Experts from the Duisburg, Germany-based Fraunhofer Institute for Microelectronic Circuits and Systems IMS have developed a transponder that is capable of identifying corrosion due to rust during the initial phase.
This transponder is able to measure and track continuously the depth of penetration of the salt ions into the concrete. This is more dependable and cost-effective technique.
A prototype transponder will be showcased at the Cologne, Germany-based EURO ID trade fair from May 4 to 6, 2010. The initial field testing of the sensor is in progress, with the sensor embedded in a test bridge made by the MPA Braunschweig.
Existing measures to detect the depth to which the ions have penetrated in concrete and the resulting damage, involves hammering the reinforced concrete by construction workers to locate cavities that denote damage due to corrosion. This process is time consuming, and is not quite effective.
Rust can cause damage to concrete bridges resulting in deadly consequences, a complete collapse at the worst. To withstand a broad range of impacts due to emissions, heavy traffic and frost concrete bridges would need to be strengthened. Besides these factors, these bridges have to deal with a range of road salts used to tackle icy roads during winter, like the most common sodium chloride used in large quantities on roads in Germany. These salts disintegrate to their ionic elements when the ice thaws. These ions penetrate the concrete and destroy its protective alkaline layer that is 5 cm thick. The steel rods that are utilized for reinforcing the concrete pad will rust when these salts pass on to them, causing damage to the structure, with the bridge collapsing under a worst case situation.
IMS researchers have created the integrated passive type of wireless transponder system, while the MPA Braunschweig’s facility for testing building materials has developed the sensor. The sensor, with very fine iron wires crisscrossing it, is installed at even distances. The extent of corrosion as well as the depth of penetration of the protective layer of the concrete is indicated by the number of defective iron wires.
According to the IMS researcher Frederic Meyer this technique helps them find out when the repair work is due. He informed that a magnetic field energizes the transponder for measuring the corrosion, instead of a battery, implying that its replacement can be avoided, enabling it to remain permanently in the concrete.