August 24, 2007

Radio Frequency Identification gains popularity

The inroads they have made in the construction industry have been small and slow so far, but RFIDs, or Radio Frequency Identification tags, are gaining wider acceptance as people devise more ways to use them.

The problem is, finding those ways takes imagination (which not everyone has) and time (which no one has enough of).

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Korky Koroluk

A concrete engineer with the Michigan Department of Transportation, fed up with what he saw as the poor performance of a wired temperature sensor he was using to track the curing of concrete, let his imagination roam — and he invited others along.

Tim Stallard talked to several RFID suppliers before getting one interested. They, in turn, turned to a Canadian outfit, International Road Dynamics, to develop some software to help achieve Stallard’s goal: a way to detect the concrete’s temperature and estimate its strength without having to wait as long as conventional testing methods require.

IRD came up with software that runs on a hand-held PC. It measures temperature data retrieved from an RFID buried in the concrete. Then it puts the data into a maturity equation that compares the readings of the poured concrete with the results of two sample cylinders which were lab-tested before construction began.

It turns out that the system gives a picture of the concrete’s maturity much faster than pouring, curing and then breaking test cylinders. The system is now widely used in Michigan, and a few other states have picked it up. Tests have been done in bridge reconstruction in New York City and on runway re-surfacing at Newark Airport.

In the airport test, an RFID tag was buried in a test cylinder which in turn was buried in the new runway slab. When the software showed the cylinder was cured, it was pulled and a compression test performed. The RFID system had accurately predicted the cure rate of the cylinder. Yet the same concrete mix in lab samples took several days longer to harden to the same strength.

Will Hansen, a professor of civil engineering at the University of Michigan, recently did a study comparing RFID maturity testers and traditional test cylinders to determine the maturity of concrete during construction of a parking garage. He found that in each of three different sections of the poured concrete, the RFID system showed the desired strength had been reached 22-25 hours from the time the RFIDs were embedded in the wet concrete. In comparison, the field-cured cylinders showed the same strength in about 67 hours.

The conclusion Hansen reached was that, with the benefit of the information yielded by the RFID system, “the contractor can start the next construction step after 25 hours instead of three days.” That represents a lot of saved time, and, of course, money.

Hansen’s study extrapolated the data over the life of the project and found a cost saving of about $2,000 per pour by using the RFID system along with just a third of the conventional test cylinders. So, depending upon how many RFID tags are used, and whether the contractor has to buy a hand-held to run the software, Hansen concluded the system will to show a return on investment after just a couple of similar jobs.

In use, the system is simplicity itself. The RFID tags, before they are buried, are told to wake up every 30 minutes, take a temperature reading and store it. Then, the next day, or whenever it’s appropriate, an engineer takes a walk through the job with a handheld, and fairly close to each tag, pushes a button to upload the information. Push another button and the system will tell him precisely how hard the concrete is at that moment.

The company that ended up bringing the maturity sensors to market is technology integrator WAKE Inc. It has quite a bit about the technology on its website including Hansen’s scientific paper for the benefit of engineers who need more detail. The paper is titled Embedded Wireless Temperature Monitoring Systems for Concrete Quality Control. The website is at www.wakeinc.com

Korky Koroluk is an Ottawa-based freelance writer. Send comments to editor@dailycommercialnews.com

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