Scientists have developed a new method for dealing with the ages-old problem of bridge corrosion which involves the application of extremely mild electrical shocks to steel cabling.
The rusting of steel bridges remains a vexing dilemma for today's civil engineers. In Australia, even a landmark as renowned and iconic as the Sydney Harbour Bridge is still not immune to the wrath of corrosion, with the Roads and Traffic Authority (RTA) announcing several years ago that rust had affected the surface of large sections of the bridge despite repeated re-painting.
In the United States, the corrosion of reinforcing steel remains a key factor behind the precarious state of much of the country's aging infrastructure. According to the 2013 Report Card for America's Infrastructure issued by the American Society of Civil Engineers, one in nine of the nation's 607,380 bridges are categorized as structurally deficient, while their average age is fast approaching half a century.
This means that on any given day US motorists traverse deficient bridge structures on more than two hundred million occasions.
Scientists at the University of Buffalo (UB) in the state of New York believe they have now developed a technique which can help to detect bridge corrosion swiftly and conveniently, long before the damage it inflicts becomes too severe.
Their method involves sending an electric shock through the steel cables of bridges. Any diminution in the strength of the charge serves to immediately signify the presence of corrosion in the cable.
Salvatore Salamone, assistant professor of civil engineering at UB, Tresor Mavinga, a UB senior civil engineering and mathematics major, and Alireza Farhidzadeh, a civil engineering graduate student, first tested out the technique used piezoelectric transducers, which are capable of converting one form of energy into another for signalling purposes.
The transducers were connected to either end of wire before a single volt of electricity was sent through its length it using ultrasonic guided waves, which are capable of traversing large distances without significant loss of energy.
They then subjected the wire to rusting by immersing it in salt water before repeating the process to discover that much of the electrical charge was subsequently lost as a result of the corrosion incurred by the wire.
In order to implement this method to real world bridges, engineers only need to attach sensors and transducers to bridge cables. They do not even need to be on-site in order to conduct corrosion inspections, since the use of electrical measurements permits remote, off-site testing.
The new technique is far more quick and convenient than existing methods, which involve costly and time-consuming visual inspections, or can entail other troublesome, physically intrusive measures such as drilling into concrete to enable the direct examination of the cables.