A Precast “Confection”

Using innovative 3D-printing technology for molds, a glistening white precast concrete tower in Brooklyn pays homage to the waterfront’s industrial history.

By Deborah Huso

A new 42-story commercial and residential tower along the East River waterfront in the Williamsburg neighborhood of Brooklyn is more than initially meets the eye. Thanks to an innovative collaboration involving large-scale 3D-printed molds, the tower pays homage to the recently restored Domino Sugar Factory building just down the street. The mixed-use structure at One South First opened for business fall 2019 and features a precast alabaster facade that glistens in the light like the sugar crystals once produced in the historic adjacent refinery.

The Domino Sugar Factory was once the world’s largest and most productive sugar refinery and helped fuel industrialization of the Brooklyn waterfront. After employing workers from around the globe for 150 years, the factory and surrounding industrial site had been vacant for more than 15 years when Two Trees Management began to work on a major redevelopment of the abandoned waterfront site.

Designing with a nod to history

Two Trees Management selected New York-based COOKFOX Architects, DPC, to help design the project. According to COOKFOX Senior Associate Arno Adkins, the firm sought to create a site-specific design that is referential to the history of the area while also focusing on sustainability. COOKFOX conducted research on the Domino Sugar Factory waterfront and decided to incorporate sugar’s crystalline molecular structure into a contemporary facade to connect the new building with its past.

“We were able to design a performative facade and fine-tune solar exposure,” Adkins explained. “As you walk around the building today, it’s subtle, but the shape of the facade changes due to solar orientation.”

Those subtleties were achieved in large part because of the use of precast concrete.

“We knew we wanted a facade that was performance-based and shaped,” Adkins said. “Other cladding options would have required more time, labor and material joints. Using precast resolved these issues and allowed us to achieve our design goals.”

To achieve the facade design, precast manufacturer Gate Precast Company selected a super white, sand-rich mix to mimic the size, shape and color of sugar crystals.

“The panels consisted of a polished finish on the proud surface of the panels and acid wash finish in the deep returns. The polished surface allows for the sun light to reflect and the acid-wash finish exposed the sand in panel, providing reflective and crisp looking panels, which gave the illusion that actual sugar crystals were attached to the precast facade,” explained Travis Fox, vice president and operation manager for Gate Precast’s northern division.

The mixed-use tower’s unique construction method grew out of a collaboration between Gate Precast and the Department of Energy’s Oak Ridge National Laboratory (ORNL). In one of the first large-scale uses of 3D-printing technology for construction, ORNL’s Manufacturing Demonstration Facility successfully showed that Big Area Additive Manufacturing (BAAM) could manufacture strong and versatile molds for precast concrete construction.

With more than 1,500 window openings, some as high as 12 feet and as wide as eight feet, and the need for more than 120 molds, the high-rise tower was an ideal candidate for the efficiencies of 3D-printing technology. COOKFOX looked to design precast concrete window panels that would not only suggest the bright, crystalline look of sugar crystals but also offer some “self-shading” to help meet sustainability goals. Had the precast manufacturer employed traditional master carpenters to build wood molds, it likely would have taken 40-plus hours per mold.

“No one had really done the large-format printing on this scale,” said Steve Schweitzer, vice president of operations at Gate. “But it would have taken longer to build the forms than the schedule allowed to produce the entire product.”

3D-printing on a large scale

According to Schweitzer, the amount of panel repetition and the large number of windows lent itself to the more efficient processes promised by 3D-printing. And with Gate’s precast manufacturing facilities located in both Kentucky and North Carolina, the 3D-printing also accelerated a construction schedule that could have been hampered by the distance.

To create the design for the 3D printers, CAD models are essentially sliced into layers to create a toolhead that drives the printer. The printer uses the toolpaths to extrude molten polymer to form the mold. It takes eight to 11 hours to print each mold and then another eight hours to machine it to the needed finish.

ORNL researchers designed molds out of carbon fiber-reinforced acrylonitrile butadiene styrene (ABS), a fairly common thermoplastic combined with carbon fibers. It took about six months to go from experimentation into production, with Gate Precast casting about 30 single-window sample panels. In total, they printed about 35 molds and built numerous others from wood for floors that had varied heights. Eighty percent of the panels with glazing were created using 3D molds.

“Tolerances were very tight, but we didn’t have the surface smoothness,” Schweitzer said. “3D-printing has that corduroy look, and you could see that at first, so Oak Ridge had to thicken the bead to get a smoother edge.”

Once ORNL established the molds’ viability for commercial use, the lab worked with Additive Engineering Solutions (AES) to print additional molds for the Domino Sugar project.

More rigorous than the wood molds they replaced, the 3D carbon fiber-based molds stood up to as many as 200 casts per mold, which was critical to maintaining the accelerated project schedule.

Adkins and Schweitzer said the team used the molds in multiple ways, too, by flipping them or turning them upside-down to get different-looking windows or taking a form out of one mold and putting it into another. The window molds on the east and west of the building were the same basic shapes. On the south elevation, the window molds had the horizontal elements projected, and on the north elevation, the vertical elements projected.

Time-saving installation

To save time, Gate Precast installed the windows into the precast punched window panels at its Kentucky and North Carolina plants. Schweitzer said the process presented challenges, particularly in terms of good weather for caulking since the panels were so large that window installations had to be completed outdoors. The caulking also had to cure for four days, so it was about a week’s cycle for window installation for each panel.

Getting the precast panels to the job site required careful planning given the tight construction site, shipping the panels to a drop lot and shuttling them to the job site. Baltimore-based E.E. Marr Erectors installed the panels using a swivel crane, which eliminated the need for, and costs of, a second tailing crane.

The construction team worked floor by floor, and because the windows were already installed, each floor was completely enclosed as it was built after joints were caulked. Bolted connections secured the panels.

Embeds extending above and below the floors accommodated all-thread rods at the back of the panels that allowed workers to slide windows into place and bolt them.

“Bolted connections led to 40% faster panel erection,” explained Russ Vines, vice president of engineering for Gate Precast. Quicker panel erection reduced the schedule while saving crane, crane operator expense and earlier dry-in of the building. Additionally, bolted connections were the best option versus welded connections if only to protect the pre-glazing. Weld splatter can cause expensive damage to glass and frames.

“The erection went relatively smoothly given the height of the building. Wind was the main nemesis,” Schweitzer said.

The future of 3D-printing for precast

Adkins said the outcome of the precast panels was sharp, crisp edges, which they were thankful for given it was the firm’s first large-scale project using 3D-printing technology.

“We’ve used it for study models, but large-format, 3D-printing of precast molds has not been widely used on a commercial scale yet,” he noted.

From the beginning of site excavation in early 2017 until receipt of the temporary certificate of occupancy was about two-and-a-half years. Schweitzer said the use of 3D-printing probably saved six months of construction time.

Precast, combined with the 3D-printing of molds, minimized construction waste, allowed Gate Precast to use skilled labor in different ways, and improved delivery and efficiency, according to Adkins. He’s excited about the future of design and construction using this new technology.

“Part of what’s fascinating is that now we’re using BIM and can share our very detailed Revit models back and forth with the manufacturer,” he explained. “We’re able to take the final model and go right into production. It’s a seamless way of going from designer to contractor.”

Deborah Huso is a freelance writer specializing in construction, real estate, finance and agriculture.