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RFID Is the Cure for San Francisco Construction Project

Shimmick Construction has deployed an active UHF system, provided by Wake, Inc., that captures the temperature of concrete as it hardens after being poured.
By Claire Swedberg
Jul 08, 2014

Accurately monitoring the curing of concrete can be critical on large construction projects. If a slab is not given sufficient time to cure, cracks can develop when the next slab is poured, which would ruin that section. Companies have typically used temperature loggers with wires from the device running into the concrete, since concrete gives off heat as it cures. But wired sensors can be too cumbersome for large projects, so in such scenarios, a concrete consultant often sets a conservative estimated curing timeline based on the material being used, as well as other conditions. This often means extra time is built into a project's timeline, in order to ensure that all concrete poured is fully cured before employees proceed to the next step.

Shimmick Construction Co. preferred not to use wired sensors or build in extra curing time for the construction of San Francisco's new TransBay Transit Center, so the company chose to deploy an RFID solution provided by Michigan technology company Wake, Inc. The system, installed when the TransBay Transit Center project launched approximately two years ago, consists of active ultrahigh-frequency (UHF) RFID tags with built-in sensors, as well as handheld readers and software to interpret the collected temperature data. The tags' sensor probes are embedded in each concrete slab and the data is read remotely, making the system more nimble than conventional data loggers.

The sensor probes of RFID tags are embedded in a poured concrete, and the data is read remotely.
Shimmick is laying 100,000 cubic yards of concrete to build a below-grade substructure for the new San Francisco transit facility. Next, the company intends to utilize the same Wake Inc. technology—the Wireless Concrete Maturity & Temperature Monitoring Solution, also known as HardTrack—during the building of concrete pilings for a bridge associated with that project.

The project consists of 16 concrete slabs that make up the building foundation. Each slab must be fully cured before the one next to it can be poured, to prevent it from being cracked by any strain from the subsequent slab. The RFID technology provides data regarding the temperature of the concrete after it has been poured, explains Charlie Marrow, Shimmick Construction's project engineer, and Wake's software then determines the poured concrete's date of maturity. That data, he says, greatly reduces the amount of time required for the cooling and hardening of concrete before the next slab can be poured.

Charlie Marrow, Shimmick Construction's project engineer
"We had been looking for options in maturity monitoring," Marrow says, as the firm prepared to launch the large TransBay Transit Center project. Shimmick Construction needed a way to ensure that the concrete laying stayed on schedule. The company's concrete consultant estimated the pouring and curing time at a conservative 30 days of curing per pour. Each slab must reach that time requirement before the adjacent section can be poured. However, he notes, this would not have worked with the company's required project timeline. Therefore, the firm began looking into technology solutions that could track the exact date of curing—which could be considerably less than 30 days—thereby enabling the next slab to be poured sooner.

Curing-time estimates can lead to unnecessarily long waits, Marrow explains, which is why companies often use data loggers. A wired data-logger solution would have been unrealistic for the TransBay Transit Center project, though, due to the size of the area and the large volume of concrete being poured—both of which would have required the spreading of many feet of electrical wiring throughout the five-foot-thick concrete laying area.

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