Birdwell explains how the high-dose macro fiber contributes to a floor’s flatness and levelness results. “In my opinion, one thing the macro fibers assist with is in holding the concrete in place, reducing the differential surface shrinkage. So if you strike off at the right elevation, the concrete will stay at that elevation,” he says.
Precision in fine grading, form set-up, and place and finish operations are all instrumental in achieving high F-Numbers. The crews from Birdwell & Associates and Skene Concrete took special steps to precisely set form grade. “Everything starts with the accuracy of grade and the accuracy of the formwork,” Birdwell says. “We made sure all the forming done on the Rigby project was within 132 of an inch. It was probably the best forming job we have ever been a part of.”
Birdwell also explains that when he is on a project with high F-Number specifications, special care is taken to make sure the laser-guided screed is properly calibrated and operated. “We find that any tool or piece of equipment can be set up and operated with varying degrees of accuracy — even something as inherently accurate as a laser-guided screed. So the more you fine tune what you’re doing and how you do it, the higher level of results you get,” he says.
Through years of systematically testing various finishing scenarios, Birdwell has identified several best practices that maximize results on his company’s floors, including slab and mix design, screed set-up, placement speed, and finishing techniques. “Quality concrete floors are a process, not a product. This slab demonstrates that perfectly,” Birdwell says.
The result was a world record floor that measured FF 123/FL 123, both the highest FL numbers and highest combined F-Numbers ever for this type of project. Birdwell & Associates holds 23 Golden Trowel awards, the second highest number of awards won over the history of the competition. The company also currently holds three world records in the competition.
Birdwell & Associates will return to the Rigby project to polish the floors, adding additional benefits to the owner. “A polished finish will prevent the rink owners from having to reapply a $10,000 to $15,000 epoxy coating every year,” Birdwell explains.
Center for New Media
First-time entrants Messerly Concrete took home two 2012 Golden Trowel Awards, including a Gold Plate award for its work at the Center for New Media on the campus of Salt Lake Community College. The 6,639-square-foot film studio floor was specified at FF 100/FL 50; Messerly Concrete achieved an FF 114/FL 79 on the project.
The Messerly Concrete crew placed the monolithic, jointless slab with a 1.5-pound traprock mix, which Todd Messerly says offers a durable wear surface with a long service life. The crew reinforced the slab with #5 rebar, 16 inches on center. The mix included a shrinkage compensating additive, which Messerly explains causes the mix to expand rather than contract for the first 10 days after placement. After 10 days, the concrete has gained enough strength so when it relaxes it doesn’t crack.
Messerly says the entire construction process for a floor like this requires a high level of attention to detail. “There is a lot of prep and care necessary on the edge forms to ensure they are at the precise elevation. We use a laser to set initial grade, then go back with a builder’s level to make sure they are dead on,” he explains.
In the placement and finishing process, Messerly Concrete crews took numerous passes with the Laser Screed at different angles, then used bump cutters and check rods to cut off any excess material. The troweling process, Messerly adds, is an important step and requires continued attention to detail to ensure flatness.