San Francisco construction project uses RFID technology to speed up completion time
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Concrete curing monitoring is the key to large construction projects. If the slab curing time is not long enough, cracks may appear when the next slab is poured. Typically, companies use wired temperature loggers running in the concrete for monitoring. But such wired sensors are too cumbersome for large construction projects. Typically, workers will conservatively estimate cure times based on materials and weather conditions. This means that there is usually an estimated cure time fixed in the project schedule to ensure that the concrete is fully cured.
For the new Transbay Transit Center in San Francisco, contractor Shimmick Corporation did not use either option, instead, it used Wake Technology to provideRFIDplan. Installed two years ago, the system includes active UHF RFID tags with built-in sensors, a handheld reader and a software that analyzes temperature data. Sensor probes are placed into each concrete slab and transmit data remotely, which also makes the system more convenient than traditional data loggers.
Next, Shimmick intends to use HardTrack, a wireless concrete maturity and temperature monitoring solution provided by Wake Technology, in the construction of concrete piles.
The project has 16 concrete slabs that are the foundation of the building. Only after the slab is completely cured, the next slab is allowed to be poured, otherwise it will cause strain. Shimmick project engineer Charlie explained that RFID technology can detect concrete temperature data, which can then be analyzed by software provided by Wake to determine the curing completion date. With this data, the waiting time for the two slabs to be poured can be greatly reduced.
“We were looking for a cure completion monitoring solution, and finally, we decided to pilot the TransBay transit center project,” Charlie said. Shimmick needed to determine when the concrete would cure in the project schedule. The company’s concrete consultant conservatively estimated each pouring and curing time at 30 days. However, he pointed out that the estimated time for this solution is much less than 30 days, so there is a lot of time saving in the middle.
Charlie explained that cure time prediction can greatly reduce wait times, which is why the company uses data loggers. Of course, wired solutions are largely inadvisable due to the difficulty of cabling.
After using the HardTrack system, Shimmick can obtain daily temperature data and upload it to the back-end system to output an Excel table. At the same time, the company not only detects the multi-point temperature of each slab, but also can see the historical record of curing temperature. Wake software can also determine cure completion based on intensity-based differential measurements and present the data on a handheld reader.
The temperature sensor label (model i-Q350TL SL) is provided by Identec Solutions. Charlie said the lithium-ion battery-powered tags are designed to be fully embedded in concrete, but he opted to leave the tags partially exposed for multiple uses to reduce cost.
Charlie said the tags have a read range long enough to be used from a few hundred feet awayReaderread. Shimmick deployed about 100 reusable tags.
After each read, the staff will transfer the data to the PC via the USB interface and upload it to Shimmick’s server.
To date, Charlie said, the system has been solidified for two weeks, half the time the company expects. In the next phase, Shimmick intends to use the tags and readers on concrete support piles to cure.
Charlie added that Wake has offered several upgrades since the system was deployed, improving some of the system’s flaws.
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