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We might have stopped talking about road salt, but councils
around the country 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 in 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 option 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, according to McNally.
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.
A further 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
- not only 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 underway 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 4-year project.
Source - The Irish Times
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