10 CityPoint Office Building
Street-level retail and 230,000 square feet of office space is being constructed at 10 CityPoint in Waltham, Massachusetts. The project features bands of large glass windows separated by architectural precast concrete spandrels in two colors that created some challenges in production and erection.
Designers for the project, which has leased its first-class office space to Wolverine Worldwide to serve as the headquarters for its Sperry Top-Sider, Saucony, Keds, and Stride Rite brands, specified precast concrete due to its economics, speed of construction, and aesthetic design, which provided the architectural feel the owners were seeking. That appearance consists of white spandrels with deep charcoal bands underneath the window lines, with a second thinner charcoal band at the base of the panels above the window line below.
Precaster Strescon Ltd. supplied 149 spandrels, all with the combined white and gray mix design, as well as 13 architectural infill panels and 14 architectural base panels. “It was a challenge to find the right mix of charcoal and white colors and mix them properly,” explains Thom Cormier, plant superintendent.
A key concern was the number of false joints in the panels, two of which divide the colors at the top and bottom while three more run through the white middle portion. The charcoal concrete was screened as it was poured to consolidate it and achieve a consistent color. But when the white concrete was added, crews found the charcoal concrete already was hardening. To alleviate this, the white was poured over the top (back side) of the charcoal concrete, wetting it enough to allow reinforcing to be added.
In addition, self-consolidating concrete was used for the white concrete, as it was found that whenever the white was mechanically vibrated into place, the existing charcoal concrete would bleed into the reveals and false joints. “We couldn’t get a crisp line for the charcoal concrete if we had to jostle it in any way,” Cormier explains. The self-consolidating concrete flowed into place with no mechanical action needed. A wood-float finish was applied to the panels.
Even with these added activities, the precaster produced six panels in a bed in eight hours. The typical panels were 26 to 35 feet long, 3 to 5 feet high, and 7 to 8 inches thick. The thickness was needed due to the false joints’ 1¾ inch-deep thickness, which offered deeper shadowlines.
Two key challenges arose during the erection, notes Philip Balboni, senior project manager for Commodore Builders, the general contractor. The first involved the design of the exterior corners to feature bevels rather than rectangular interfaces. That produced 45-degree angles on the edges with less concrete. “We had to be careful in handling and aligning the panels in those locations to ensure no damage, as they were more fragile,” he says.
The other challenge involved working out how sealant joints would be applied. Ultimately, the sealant was applied to the back side of the reveals on the panels except at the corners, where the sealant joints follow the reveals. “For the majority of the façade, having the sealant at the back of the reveals isn’t noticeable, but at the exterior corners it creates too much of a shadow line,” Balboni explains.
The project is on track to be completed in December 2015, with the precast concrete erection helping to say on schedule. “The installation went very well. No issues developed because we had worked things out in advance,” Balboni says. “It was a very favorable experience working with Strescon, as it always is.”
Cormier agrees. “The project had challenges, but everything worked out well. And the charcoal color is very impressive. It’s difficult to achieve a consistent, dark black across such long lengths, but this worked very well.”
Architectural Precast Elements:
• 149 architectural panels.
• 13 architectural infill panels.
• 13 architectural base panels.