RFID helped set the foundation for the 1,776-foot Freedom Tower that was constructed where the World Trade Center’s original Twin Towers stood in New York City. Builders embedded thousands of active RFID (Radio Frequency Identification) tags with temperature sensors in the concrete used for the foundation and throughout the structure so they could easily and accurately monitor the curing process. The RFID tags were embedded in poured and pre-form concrete used throughout the structure, which has more than 2.6 million square feet of office and observation space and opened in 2011.
THE USE OF TAGS
The Freedom Tower has a blast-resistant steel frame with thousands of yards of concrete used for the foundation, stairwells, elevator shafts, and other elements. Many grades of concrete were used, and each cured differently. During construction, concrete had to be completely cured before it could bear a load. The process took weeks, which necessitated frequent monitoring to keep construction schedules up-to-date.
“There are several ways to monitor concrete maturity. One is mathematical models, which have a high margin of error. Construction tends to take longer because there’s such a safety factor to make sure the concrete is really cured,” says Peter Linke, president of IDENTEC SOLUTIONS, whose i-Q32 Temperature Tracking Tags and readers were used in the project. “There are also wired sensors, but the wire has to be removed later. You can throw our tags right into the concrete and read them with a handheld.”
Linke estimates the tags are embedded in concrete between 8 and 12 feet thick. The concrete used in the Freedom Tower is a much stronger grade than typically used in construction, and is a record for a New York City facility, but did not pose a problem for getting reads from the active UHF tags.
“We didn’t have to modify our product at all,” says Linke.
The HardTrack CMMS (Concrete Maturity Monitoring System) allows users to save time by communicating with RFID sensor tags buried in the concrete; the tags are waterproof and made for harsh environments.
CONCRETE MATURITY MONITORING SYSTEM
The tags are integral to the Concrete Maturity Monitoring System (HardTrack) developed by Wake, Inc., a data collection solutions provider. Wake developed the system several years ago and has provided it for other construction projects.
Linke says the Freedom Tower project was not a typical application for long-range active RFID, but it helped people see how the technology could be used. “When people think of RFID, they tend to think about EPC and Wal-Mart-type applications,” he says. “We see RFID as an intelligent wireless product rather than a standard EPC identifier. It is like a computer you can embed in something and access wirelessly.”
Once curing is complete, builders have no further use for the RFID tags, which are left encased in the concrete. Linke says they will remain readable for years, as long as the battery lasts.
HOW THE RFID TAG WORKS
An RFID tag uses an advanced radio frequency technology and operates at 915 MHz. It includes a temperature logger with an accuracy that exceeds the ASTM C1074-93 requirements. With the recommended hardware, the average range should be at least 15 to 20 feet. The RFID tag contains 32 KB of memory and a battery life of 6+ years. The tag can be programmed to wake up, read, and record the ambient temperature at user defined intervals. The stored information can be read at any time, with no restrictions on the number of times it is read.
Utilizing the most advanced durable wireless thermocouple technology, both handheld and remote wireless solutions are available allowing for ease of collecting temperature logs in the field or while working from your office location. There is no need to directly connect a device to each thermocouple to download temperature logs.
Each sealed temperature logger contains its own wireless RFID chip and either an internal thermocouple or external probe with a lead available in lengths of 2 meters, 4 meters, 6 meters, or 8 meters. ■
For More Information
For more information on Wake, Inc. and the HardTrack Maturity & Temperature Monitoring Solution, call 800.957.5606 in the USA; 647.931.6995 in Canada; and +61 4 0059 9007 in Australia and New Zealand. Email: firstname.lastname@example.org Web: www.wakeinc.com.
Modern Contractor Solutions, December 2014
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