A barge hit the Webbers Falls, Okla., bridge May 26, felling four spans (ENR 6/3 p. 11). The state hired Gilbert Central Corp., a Ft. Worth, Tex.-based unit of Peter Kiewit Sons Inc., to replace spans, piers and caps.

Photo courtesy of Newmerical Technologies)

Gilbert used Stillwater, Okla.-based Nomadics Construction Labs' intelliRock logger, a 35mm film canister-sized sensor containing battery, microprocessor, and temperature sensor, to measure, calculate and record concrete maturity continuously. Each logger measures a structure's time-temperature history for up to two months.

The loggers are installed by tying them to rebar before the pour or inserting them into wet concrete afterward. Wires can run as far as 100 ft. to where a handheld reader can download data for either direct reading or uploading to a computer. The reader-activated sensor will download up to 200 sets of logger data.

The reader and 25 loggers cost about $1,500. "We placed several sensors in each major element and they worked great," says Pete Byers, Oklahoma Dept. of Transportation's resident engineer, contracted from Cobb Engineering Co., Oklahoma City. The system helped accelerate the job, he says.

Steve Trost, NCL chief scientist, says one advantage the system has over concrete cylinder specimens is that it measures strength in the structure. "Typically a structure gains strength at a faster rate than a specimen and that allows you to strip forms and load the structure at just the right time," Trost says.