Cost-effective Warning System for Rust Developed
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| Image copyrighted/courtesy of Fraunhofer IMS |
Concrete bridges have to be strong enough to cope with a wide variety of different impacts: frost, heavy traffic and emissions all take their toll on these structures. And then there are the various types of road salt used in winter to combat icy roads. The most common of these is sodium chloride, which is deployed in large amounts on Germany's roads. When the ice thaws, these salts break down into their ionic components that penetrate the concrete, destroying its five-centimeter thick protective alkaline layer. Any salt that leaches through to the steel rods used to reinforce the concrete pad will cause them to rust, resulting in structural damage. The result is cracks. In a worst-case scenario the bridge itself could collapse.
Until now there has been no effective test to determine how deep the ions have penetrated the concrete and what damage they have already caused. Current practice is time-consuming and involves construction workers hammering on the reinforced concrete in search of cavities, which are a sure sign of corrosion damage. But experts at the Fraunhofer Institute for Microelectronic Circuits and Systems IMS in Duisburg have now hit upon a more reliable and cost-effective method for detecting rust corrosion at an early stage.
With a new sensor-transponder they can continuously measure and monitor how deep the ions have penetrated the concrete. While the sensor was developed by the building materials testing facility in Braunschweig (MPA Braunschweig), the integrated passive wireless transponder system is the work of IMS researchers. The sensor itself is crisscrossed by very fine iron wires, laid down at even distances.
When 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 concrete's protective layer has been penetrated. This would aid the workers to determine when the next repair work needs to be carried out.
The transponder transmits the measured data by wireless to the reading device carried by the construction workers. The transponder does not get the energy it needs to measure the corrosion from a battery, but from a magnetic field. This means it does not need to be replaced and can remain within the concrete structure permanently.
This technology will help to reduce the rate of bridge collapsing.
New technology aids 110-foot bridge to withstand magnitude-8.0 earthquake.
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| Photo by Mike Wolterbeek, University of Nevada, Reno |
After a succession of eight separate earthquake simulations, a 110-foot long, 200-ton concrete bridge model at the University of Nevada, Reno withstood a powerful jolting, three times the acceleration of the disastrous 1994 magnitude 6.9 Northridge, Calif. earthquake, and survived in good condition.
The University of Nevada research team is experimenting with and testing a number of materials and innovations to potentially revolutionize seismic design of future bridges to help protect lives, prevent damage and avoid bridge closure even when there is a strong earthquake.
This bridge is the use of glass and carbon fibers to support the bridge, precast columns, segmental columns and special steel pipe-pin connections in a high seismic setting. The bridge model is shaken with bidirectional forces to realistically simulate an earthquake.
The succesion in the test will lead to engineers having the ability to build safer bridges, to reduce lives lost during earthquakes.
(Articles courtesy of ScienceDaily)
