UCD researchers are designing 'smart bridges' that can indicate when repairs are needed, writes DICK AHLSTROM
WE MIGHT have stopped talking about road salt, but councils around the State have not stopped using it. And with it comes the potential for corrosion of bridges as the supporting steel embedded in the concrete literally rusts away.
Salt corrosion of bridge steel is an inevitable but hidden process, making its detection a challenge for council engineers. A UCD researcher has come up with a possible answer – a bridge that can tell engineers when it needs repairs.
Dr Ciaran McNally in the university’s School of Architecture, Landscape and Civil Engineering leads a €3.25 million EU-funded research effort to develop smart bridges. It involves the work of seven university and private sector partners in six countries. The goal is to develop ways to detect hidden bridge corrosion long before it gets so bad that the entire bridge needs replacement. Behind this however is the benefit of training 14 PhD students, says McNally.
“It is a Marie Curie initial training network,” he explains. It is known as Team (Training in European Asset Management). “It is all about overall PhD training.”
They learn about company start-ups, intellectual property, entrepreneurship and innovation. “These are the skills needed in the future to bring this technology forward.”
In the process the partners and their PhD researchers – including five who will work in Ireland – will deliver real research and help save money on bridge repair long term.
“The whole idea is that it costs so much to put in the road and bridge network. It is a method of managing it the best way to get the most out of it,” McNally says.
Bridges are checked, but the damage can get too far before being detected, meaning the structure will need full replacement. “The whole industry of repairing bridges is massive, in the billions [of euro],” he says. “One of the main sources of deterioration is road salt.”
Dissolved salt penetrates through the surrounding concrete to corrode the steel reinforcing bars. “Essentially it will lose its performance over time and get exponentially worse,” he says. Road authorities have to rely on a “best guess” approach to picking up on damage. “This is all about putting sensors into the roads and bridges so the repairs can be done in time and avoid replacement.
“Putting sensors in allows you for example to make decisions at the right time. If you get there a bit earlier the cost will be less.”
An earlier warning might have prevented the deaths of 13 people and injuries to another 145 in the I-35 bridge collapse in Minneapolis, Minnesota, on August 1st, 2007.
This spectacular bridge failure was mainly attributed to design faults, with investigators less able to quantify corrosion damage.
The incident does show however the need for methods to detect problems before they happen. The Team consortium is looking at a number of options to detect the condition of a reinforced concrete bridge.
One involves using sensors embedded in the concrete that can measure electric current. The salt-steel reaction works like a battery to produce a current and this can be measured, McNally says.
Another approach is to measure bridge displacement when a lorry passes. Corroding steel loses stiffness and rigidity so a bridge in need of repair would flex more, he says.
One of the research partners, an Austrian company, has developed special sensors that can be embedded into road tarmac. They detect strains and may be able to predict surface failure before it happens.
Another approach involves trying to detect lorry wheel “rutting” in the tarmac surface even before this becomes visible.
McNally was very happy to have won the Marie Curie award given its value but also the distinction in winning one.
“They are quite competitive, the success rate is only 6 per cent,” he says.
The project got under way last November and five PhD candidates have been recruited so far. The remaining nine will be chosen before the end of this month for the four-year project.