...monitoring of important structures can be easily justified. "Only looking at short term hardware costs, sensors and acquisition systems may represent about 1% of the total construction cost of a structure....Considering the savings and higher structural safety levels they may provide, this is not expensive," he says.
 |  |
| Hot And Cold. Fluor Corp has tested maturity sensors in the tropics. Cold weather trials start now. Photo left by Greg Deminchuk,Fluor Canada, Ltd., right courtesy of Fiatech | |
Cussons test uses retrofitted sensors that track, almost by the minute, values from within the bridge. They trace variations in electrical potential, resistance, moisture and temperature. Those readings are helping map the DNA of deterioration, which could improve construction and repair techniques and lead to immense cost savings, he says.
While Cusson waits for the technology to gain a following, others are plunging in. "We are really excited about it," says George Rollins, global manager for technology services at Fluor Corp., Aliso Viejo, Calif. "It [embedded sensors] could be a huge benefit."
Fluor has been conducting trials with one application of sensors gaining buy-in among state highway officials. It uses arrays of embedded readers to gauge concrete maturity from within the form itself, rather than extrapolate developing strength from test samples. Fluor is testing the IntelliRock data logger "concrete maturity method" system, of Engius LLC, Stillwater, Okla. (ENR 8/19/02 p. 23).
Quick Results
More than thermometers, the sensors are film-can-sized devices with batteries, processors and memory. They are pre-calibrated with tests beforehand to the formulation being poured. Data is captured by connecting wires leading out of the concrete to hand-held readers. The system allows users to quickly and accurately gauge the state of the cure in real-time. "It allows us to remove forms earlier, to load the concrete earlier, or maybe just put construction tools on it soonerand all that improves our schedule," Rollins says.
After a successful hot-weather trial with the system on a pharmaceutical plant in Puerto Rico in late 2003, Fluor technology managers have recommended it to project managers. Now, Fluor is starting new trials on very cold weather construction in Kazakhstan and Canada.
 |
Like the wireless sensor trials at the visitors center in Washington and the plant project in Puerto Rico, the cold weather trials are conducted jointly with product vendors and FIATECH, a Houston-based consortium that fosters the adoption of promising new construction technology in facilities and infrastructure construction. Under its "Smart Chips" testing program, FIATECH taps vendors, contractors and academic partners to conduct carefully designed field trials. Its aim is to resolve questions about reliability and developand sharetechniques for putting new technology to good use. The cold-weather trials in Canada are one of the latest examples.
 |  |
| Changes. Wireless sensors monitor support steel response to cold during winter pour at U.S. Capitol Visitors Center so engineers can analyze impact. (Photo above courtesy of the Office of the Architect of the Capitol; photos below courtesy of Fiatech) | |
"It doesnt get any colder than here," says Scott Hounsell, a Fluor construction engineering manager for revamps, working on an Imperial Oil refinery site in Strathcona, Alberta. In the trial to begin later this month, embedded sensors will be placed in forms for grade beams and equipment bases and "table-top" slabs on the refinery site, which is being expanded for desulfurization of diesel fuel.
Winter temperatures at the site dip below -30°C. The practice, Hounsell says, is to build insulated tarp shelters to "heat and hoard," the pour. Ambient temperatures are brought to about 5C° and kept for seven days, or until the concrete obtains 70% of ultimate strength. In the upcoming trial, the data loggers will be used in tandem with traditional cylinder-breaks and lab tests to compare the systems.
The other cold-weather trial, which Fluor is conducting on its own because of the difficulties of coordinating a group study at the location, is at a $3.5-billion gas-oil separation plant in Tentiz, Kazakhstan. "The project is huge," Rollins says. "There is a lot of concrete there."
