In Kansas City, Bottorff Construction provided all concrete work on a high profile, 276-unit, super energy-efficient multi-family apartment at Second and Delaware.
Bottorff Challenges Test Results
The team faced a number of challenges with their schedule during winter when temperatures dropped into the low 20°F (-6°C) range. Bottorff had 14 columns poured as part of their 200-level concrete work. Construction stopped when their inspection agency reported that traditional break-tests were low, suggesting the concrete had frozen or was in some way deficient. Bottorff challenged whether field-cured cylinders were following ACI guidelines for cold weather conditions and accurately reflecting strength of in-place concrete.
“The agency would cast their cylinders and set them outside, next to our forms and try to wrap them with our blankets to protect them,” says J.J. Hanses Field Superintendent for Bottorff. “We told them that they were going to break low doing their cylinders that way,” he adds.
Rip and Replace
Based on the lab results, Bottorff was confronted with the possibility of having to “rip and replace” all level-200 concrete work at a tremendous cost. Non-destructive testing with a rebound hammer confirmed that compressive strength had been achieved as the team had expected.
Geiger Ready-Mix Recommends a Better Way
Wanting to avoid further delays and discrepancies with the inspection agency’s lab results, Bottorff turned to Geiger Ready-Mix, one of the foremost concrete suppliers in Kansas City.
“The conditions here made it extremely difficult, if not unrealistic, for field-cured cylinders to capture the accurate in-place strength results required,” says William Pettit, Project Manager for Bottorff. “With a tight schedule to maintain, the time-consuming process of cylinder break tests was not meeting our needs, nor the building owners’,” adds Pettit.
Geiger recommended Giatec SmartRock™ Plus to enable Bottorff to capture real-time data on concrete temperature and strength. SmartRock™ Plus enables contractors to attach small, unobtrusive wireless sensors to the rebars of concrete pours. Data is uploaded immediately to an easy-to-use app on any Android or iOS device where it can be accessed at any time. The sensors have a battery life of up to four months. All data is ASTM C1074 compliant and approved by ACI 318, CSAA23.1 and the majority of USDOT specifications.
“We feel providing solutions that make our customer’s jobs easier, while having a positive impact on their bottom line, is one of the best ways we can add value,” says Jim Jauernig, General Sales Manager, Geiger Ready-Mix. “This value solidifies our relationship with them – and in this case, SmartRock™ Plus was a perfect fit.”
Bottorff used a total of 28 SmartRock™ Plus sensors for the next phase of concrete work – with a hard target of achieving 8,000 psi in 28-days.
Prior to using maturity sensors, Bottorff was waiting three days to strip concrete formwork – which delayed the entire project because the welder and others couldn’t access the site. “Instead, with SmartRock™ Plus, we had actual, reliable information in real-time which enabled us to make immediate decisions and strip forms the next day, based solely on the probe data,” confirms Pettit.
Agency Test Results Match SmartRock™ Plus Data
Bottorff and their testing agency continued to use break tests for absolute verification of concrete strength. When these results were available, SmartRock™ Plus sensors reported the same results within 200 psi.
“By using SmartRock™ Plus, rather than relying solely on traditional break tests, there was no hold-up in our schedule – none whatsoever” said Hanses.
“Using SmartRock™ Plus took a month off the schedule, saving tens of thousands of dollars”William Pettit, Project Manager, Bottorff Construction
The fact that SmartRock™ Plus provided a reliable counterpoint to lab test results was invaluable – enabling Bottorff to provide assurances to the building owner about achieving concrete strength. This allowed the team to move forward confidently with a more aggressive schedule on this very high-profile project.
Bottorff plans to continue to use SmartRock™ Plus sensors in all future projects.