Paula Wallis, TunnelTalk

Radio frequency identification (RFID) technology is being used to track everything from, shipping containers across oceans and prized livestock through their lifecycle, to heavy machinery and now concrete tunnel segments. On the fabrication floor of Armtec's facility in Woodstock, Ontario, finger sized RFID tags are being imbedded into each of the 58,000 precast concrete segments for Toronto's Spadina Line subway extension. The tags will track each segment from fabrication and storage to shipment and installation and will provide valuable information during the maintenance cycles and design life of the twin-tube running tunnels.

RFID tags secured to the rebar cage

"We have essentially digitized our old fashioned hand written tracking systems," said Phil Sheldon, Operations Manager of Armtec's Woodstock facility. "Concrete components do not go missing that often, but they do get misplaced and when we lose track of a piece it can be very disruptive."

RFID was not a design requirement originally, but when Toronto Transit Commission (TTC) learned the fabricator had the capability, it requested the technology, said Sheldon. As far as he knows it is the first use of RFID in precast concrete segments for the tunneling industry.

The tags cost about a dollar a piece and are secured to the rebar cages of the segments at a designated location and encased in the concrete, which protects them against wind, rain and other adverse conditions.

"Using a handheld scanner, workers can instantly read an imbedded tag, review and update information, such as when and where it was fabricated, where it is located in the storage yard and when it was shipped," said Sheldon. "Our quality control team is also using the system to monitor quality during the fabrication process."

Tags are read by a handheld scanner

In 2010, TTC awarded Armtec the $43 million contract to supply the 58,000 liner segments over a two-year period for the twin 6.5km (4 mile) tunnels. To date, the fabricator has completed about 30,400 or a little more than half. "The contract requires handling hundreds of pieces per day," said Sheldon. "The tracking of those TTC pieces would have been difficult without RFID technology."

The benefits of RFID technology are passed along as the segments change hands says Ajit Pardasani, an engineer with Canada's National Research Council that is collaborating with Armtec to develop the system.

"After the unit is shipped to the construction site, now it is the contractor who needs to manage inventory," said Pardasani. "The contractor can digitally track what has been received, what, if anything, has been rejected, and what segments were damage in shipping. It can also locate where specifically the segments are installed in the tunnel, both its distance from the portal and its position in the segmental ring. The asset then changes hands again to the Owner who now has a digital record of the entire life of the segment to this point."

Tags can be read through the concrete

The greatest benefit however to the Owner is during the maintenance of the completed facility. Individual segments can be scanned and maintenance records updated to include current condition and location of any water leaks for example. "The Owner can do more accurate analysis by reviewing the historical record and by determining how many segments are experiencing the same problem, and if the problem is occurring in other sections of the tunnel," said Pardasani.

RFID technology has been in existence for a more than a decade but the falling cost of equipment and tags, the improved performance to a reliability of up to 99.9%, and a stable international standard for UHF passive RFID in 2010, has sparked renewed interest.

"The cost of implementing an RFID system runs anywhere from $200,000 to $300,000," said Pardasani, "and the tags can range in price from less than a dollar to up to $50 a piece depending on how sophisticated they are. But there is tremendous potential for reducing lost time and productivity and increasing efficiencies with such systems."

Segments at Armtec's 50 acre Woodstock plant

Armtec adopted RFID two and half years ago as a way of keeping track of its standard products including bridge girders and parking decks in its 20 hectare (50 acre) storage yard. Before RFID, Armtec estimates the annual cost of missing inventory at its Woodstock site was about $260,000 a year, including about $60,000 in penalties for late deliveries.

"A bridge girder is about 30m (98ft) long and weighs more than 50,000kg (55 ton)," said Sheldon, "but we sometimes lost them. After placing something in the yard, the crane operator would mark its location in a notebook. If the notebook was misplace or lost, or wasn't updated when the unit was relocated or shipped, we were in trouble.

Now I can be sitting in a coffee shop with a smart phone and can log on to the database, select a project and know in a matter of minutes what was cast today, review the quality control record, and know where those new segments are in our yard, something that would have taken me hours to do with our old hand written tracking system."

Custom-made trailers carry segments to site

Armtec is using a passive RFID system. Passive tags have no power source, unlike active tags that can constantly transmit their location via satellite, similar to GPS systems in cars. Active RFID tags are $30 to $50 and their batteries have a finite life span.

"We were looking for a simple tag that would survive in concrete," said Sheldon. "This system gives the Owner the ability to scan the segments 10, 20, 50 years from now and access its information."

RFIDs are finding greater applications in the construction industry. Active tags are playing a key role in the construction of the Freedom Tower, where the World Trade Center's Twin Towers once stood. About 20,000 tags supplied by an Austrian firm, Identec Solutions AG, are being used to monitor concrete curing. As floor slabs and walls are poured a tag is toss into the concrete. The battery-powered tags can transmit temperatures through up to 20ft of concrete to a handheld device where engineers can determine if the concrete is sufficiently cured to carry a load.

Embedding RFID tags in the Woodstock segment casting plant

Still the construction industry, as a whole has been slow to adopt the technology for several reasons said Pardasani.

"The major drawback is that there is no one unified system," he said. "There are so many stakeholders involved in the implementation of a project. The various entities come together for this one project and they then move on to something else. Each entity has its own unique system. Fabricators have a system that works best for them; contactors are using something else and owners something else again, so there is no seamless flow of information. Many of the systems are proprietary and mostly they are paper-based systems. Project management is one exception where you find information technology systems being embraced."

But with greater pressure to control costs and to speed up construction timelines Pardasani and Sheldon can see a time in the not to distant future when RFIDs will be specified in tenders.

References

Tunneling to commence in Toronto - TunnelTalk, May 2011
Spadina extension awarded in Toronto - TunnelTalk, Nov 2010

National Research Council Canada

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