Sodium chloride is one of the most common salts used in winter to combat icy roads. But when the ice thaws, the salts break down into their ionic components, penetrating concrete. Any salt that leaches through to a bridge's steel reinforcing rods will cause them to rust, resulting in structural damage.
Until now there have been no effective tests to determine how deep the ions have penetrated the concrete and what damage they have already caused. But experts at the Fraunhofer Institute for Microelectronic Circuits and Systems in Duisburg, Germany, and the building materials testing facility in Braunschweig have developed a sensor-transponder that can continuously measure how deep the ions penetrate the concrete.
The researchers said the sensor is crisscrossed by very fine iron wires, laid down at even distances.
"If the dissolved salts reach the iron wires, these begin to corrode and break. The number of defective iron wires is an indicator of the extent of corrosion and the depth to which (the salts have) penetrated," Frederic Meyer, one of the researchers, said.
The researchers will present a prototype in Cologne during the May 4-6 European Trade Fair and Science Forum for Automatic Identification.