If there's a bedrock axiom to highway repairs, it's "be precise or pay the price." Overtime and contract penalties consume margins. And reputations are damaged when state transportation officials field calls from irate commuters (aka taxpayers) because the contractor failed to finish overnight repairs on time. These prospects faced Phoenix Construction of Lynn Haven, Fla., when it began year-long repairs on a stretch of I-75 in Tampa in 2006. Phoenix Construction's precision solution: give its concrete slabs a "brain" called intelliRock . With it, Phoenix Construction completed the project 75 days ahead of schedule.
The Florida Department of Transportation's (FDOT) project specifications were to repair a four-mile stretch of I-75, just south of I-4. Repair work began with a single lane shutdown at 8 p.m. and double lane closure at 11 p.m. All lanes had to be reopened to traffic by 5:30 a.m. the next morning. That depended on concrete cylinder samples testing to 2,200 psi. Failure to meet this target accrued penalties of $10,000 for the first 15 minutes and $5,000 for every 15 minutes after that. Acceptance cylinders had to achieve 3,000 psi 24 hours after each pour to authorize contractor payment.
Giving Concrete a "Brain"
Phoenix negotiated a zero dollar spec change that included intelliRock – a 1.5-in. encased data logger inserted in concrete. Developed by Stillwater, Okla.-based Engius, the data logger uses proprietary sensors to measure and log concrete strength in real-time by using the maturity method based on ACI and ASTM standards. "The concrete supplier provided a calibration curve that gave the Celsius-hour maturity target that intelliRock measured precisely," said Brian Wells of Tally Engineering, the concrete testing lab.
IntelliRock was placed in the last slab poured each night. After four nights, Phoenix gained enough data to optimize slab production. "The best thing intelliRock did for me is plan my slab production," said Rodger Calhoun, I-75 project superintendent for Phoenix Construction. "The concrete mix was designed to reach maturity in six hours or less. Depending on environmental conditions, intelliRock told me I was achieving maturity in 4.2 hours, giving me an extra hour and 45 minutes on some nights to pour slabs."
" IntelliRock measured maturity strength every minute, eliminating the need for the more time-consuming cast and break cylinders to meet road opening specifications," said David Hitchcock of Genesis CEI, which performed verification testing for FDOT. " Intellirock removed the human error associated with moving concrete cylinders before sufficient strength is achieved."
The data logger delivered added value when the "acceptance strength" cylinders for contractor payment were transported nightly for off-site testing. Acceptance cylinders had to be tested after 24 hours, which meant double, and sometimes triple, overtime for cylinders poured at 2 a.m. " IntelliRock in the cylinders demonstrated the concrete had achieved its 3,000 psi 'acceptance strength' in 12 to 14 hours," Hitchcock said. "That meant the cylinders could be broken in the afternoon, avoiding considerable after-hours overtime." "IntelliRock saved a minimum two hours overtime for each night of concrete production," Calhoun said.
IntelliRock delivered a smart solution for the contactor, the client and commuters in Tampa.