Just like Kermit the Frog said, “It’s not easy being green.” Who knew concrete and frogs had so much in common?
To develop the green mix design used at the Port St. Lucie, Florida, heart sculpture, a lot of brainstorming and testing had to take place before it could even be poured on a jobsite.
It all started over a year ago when Richard Rhoades, vice president at Adena Corp. in Florida, began working with a team of players to see how they could come up with a more carbon-friendly mix for work in the thematic entertainment industry.
The first step was to dial in the right ratios of cement and slag.
“We teamed up with Cemex and started figuring out how much cement we could remove out of the concrete for our decorative mixes. We started utilizing slag because it is white and pure, and our colorants would be stable,” Rhodes said.
It took about six months of testing, but they finally achieved the results they were looking for. Their results got them to 50% slag and 50% cement. A .48 water-to-cement ratio was used, and a plasticizer, finishing aid, and other proprietary admixtures from Cemex were all added into the mix at the plant.
“After that we thought, OK. What can we do to remove steel?” Rhoades says.
Their research led them to testing 43mm basalt fibers. “They are heavy, so they don’t float to the surface,” says Rhoades.
In the end they came up with a design that they say was equal to or better than a traditional 100% cement formula. It was tested for how it reacted to colorants, foot traffic wearability, strength, and shrinkage.
“We found a negligible difference between the two mixes,” Rhoades says.
Safe and secure
With the mix design solidified, Rhoades reached out to Sheltra at ReForm Composites Engineering to inquire about adding PolyDowel at the slab joints.
“Concrete dowels are typically made of steel,” Sheltra says. “Composite options exist, but they are
too brittle to perform well in load-transfer applications. We developed a dowel with continuous fiber-reinforced thermoplastic, which uses recyclable thermoplastic resins similar to those found in water bottles.”
CFRTC dowels offer the same benefits people expect from composites, Sheltra continues. “They’re easy to install and rust-free—but with far greater toughness and full recyclability. Concrete joints using PolyDowel have even shown performance that exceeds steel options.”
While both the mix design and PolyDowel have been used in projects before, the Port St. Lucie Heart in the Park is the first application where they both came together outside of the themed entertainment industry.
“As we look toward the future of construction, structural engineers will naturally ask about real-world performance,” Sheltra says. “Laboratory studies can predict this well, but true confidence comes from
precedent. The Heart project helps set that precedent.”
