By using sensors embedded within concrete at the time of construction, infrastructure operators might be able to avoid the kind of large-scale overhaul that is taking place at the Hammersmith Flyover, in London, which has been damaged by water-induced corrosion and closed for repairs ahead of the 2012 Olympics. Wikimedia Commons
If adopted, corrosion sensors embedded in concrete could detect structural instability years before that weakness is visible to inspectors.
April 10, 2012—The upcoming Olympics will be an opportunity for London to show off its engineering prowess, as numerous housing facilities and sports stadiums have sprung up seemingly overnight since the city was awarded the Games in 2005.
With just months to go before the July 27 opening ceremony, finishing touches are being put on the fields and tracks, which could host some historic sports moments. But the deadline has also put pressure on such infrastructure organizations as Transport for London to make sure all of the city’s main arteries are operating at full capacity.
One of those roads is the Hammersmith Flyover, an approach from the western suburbs into the city proper. A 200 m long section of that elevated roadway has been out of commission for months, and crews are only now preparing to replace the concrete and reinforce other pieces of the bridge ahead of the Olympics.
Ken Grattan, a physics professor and dean of the School of Informatics at City University London—who knows the road well because of his commute—says his school hopes to make this sort of emergency repair a thing of the past. A four-year research effort into corrosion monitoring systems for structures in extreme marine environments recently revealed that an early warning system to prevent this sort of decay is within reach. “That structure has not been monitored, and that structure is not able to handle the loading it should be handling,” Grattan says. “If you were driving in every morning from the west, as I used to do, it’s going to take you much longer to get into work. That’s how this sort of issue affects everyone.”
Lead researcher Tong Sun, along with partners at Queen’s University Belfast, were sponsored by the Engineering and Physical Sciences Research Council with a grant of nearly £500,000 (U.S.$ 793,846). In a press release, Sun said the key to success was finding polymer-based sensors that could withstand high alkaline levels, something found in environments subjected to constant moisture.
“We’ve got quite wide experience from other projects—whether we’re looking at very high temperatures or we’re looking at high levels of alkalinity or other less pleasant environments,” says Grattan. “Our experience has enabled us to design and build sensors able to deal with these harsh environments.”
The sensors developed by the research team, which should last for several years compared to currently available models which only last for a few weeks, are attached to the rebar embedded in concrete during the construction process. In concert with other sensors, they create a circuit that links up with an interrogation system that in turn communicates wirelessly with a base unit, which can then send findings to a server over the Internet, Grattan explains.
It’s a major improvement over visual inspections, especially for 50-year-old bridges like the one in Hammersmith. “If they had picked up that there were problems with rusting occurring, they could have got to a situation in which they could have improved the quality of the structure, stopped any further degradation of the reinforcement, and done it all in a very timely and organized way,” says Grattan.
Now the challenge is to take the study’s findings and convince industry leaders that it’s worth investing in the new technology.
“The main problem, of course, is the civil engineering industry is a pretty conservative industry,” Grattan says. “And it takes time for them to accept the fact that some of these new sensors and monitoring systems are systems that will enable us to do things that are of real value.”
Workshops have already been held with some major builders, and the scientists will continue to take advantage of a “follow-on” funding grant to pitch their system to those in the profession. “It’s really up to the industry to understand how big the threat is and look at these solutions to figure out [this] will help them move forward more quickly,” Grattan says.
Grattan likened the future of sensors that can be embedded directly into concrete to what has happened in the most recent generation of automobiles. “Thirty or 40 years ago, the only sensors on a car were the oil pressure sensor and perhaps a temperature sensor,” he says. “Now on even the most ordinary of automobiles, they’re very much stuffed full of sensors.”
As a result, he adds, “You get the best performance out of the car. You get good comfort out of the car, you get warning that anything is going wrong. That’s in one generation—and that’s in a car worth $30,000.
“If you look at buildings worth vastly more than that, I’d expect we’re going to see the actual structures full of sensors which will give the maintenance engineers a real sense of how sound these buildings are,” he says. Such sensors would streamline maintenance schedules and possibly obviate the need complete overhauls, he says. The goal is to build the sensors in during initial construction, follow their reports on structural stability, and head off repairs before an entire section of a bridge needs to be replaced.
“It’s all about just keeping our roads going and reducing the time it takes to get into work, or get into the shops, or just driving on the roads in a normal leisure pursuit,” says Grattan.