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Case Studies  > NYC's Helena Conveys Strength in Design
A Learning Curve With Slag Cement
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Photo courtesy of Fox &
Fowle Associates

601 W. 57th - Manhattan, New York

Located in the heart of Manhattan at the corner of West 57th and 11th, The Helena is a 600,000-square-foot residential development with 597 rental apartments, underground parking and retail space at the building’s base which adds vitality to the Avenue’s street life.

The Helena is the first phase of the redevelopment of a former full-block industrial site which is currently master planned for mixed-use development. In order to reduce the perceived mass of the building, it was designed as a collection of interlocking volumes with varied mass, numerous high performance windows, and balconies.

Instead of using Fly Ash, the more commonly used supplementary cementitious material in the New York area, the concrete contractor decided to take on the challenge of using 45 percent slag cement mix on the project.

Jim Werner, sales representative for slag cement supplier Lehigh Cement (Allentown, Penn.), stated that “This was the first time slag cement was used in such a high percentage in a New York City high rise of this magnitude: "We knew it would work, we just didn't know how well it would work. With the mix we're using now, we're seeing the benefit of slag cement at one to three days, instead of the usual seven to 28 days. High early strengths are a priority on this project, which hinges on two-day construction cycles that can't afford significant slowdowns as temperatures drop.”

Bob Mannino, project engineer for concrete contractor, Pinnacle Industries (Harrison, NY), mentioned that in exchange for the material's benefits, the crews experienced a learning curve with slag cement on The Helena. Traffic in Manhattan prohibits the complete batching of water and chemicals at the ready-mix plant, so concrete truck drivers had to "learn the feel of this material. You have such a high dose of slag cement that as the concrete mixes in the truck, it sounds like a higher slump than it is." Mannino added that regardless, the benefits of the mix are worth it.

When construction started, the team thought that cold temperatures might necessitate a reduction in the amount of slag cement. “Slag cement performs better in hot weather, so we weren’t sure how it would perform coming into the winter months,” explains Jim Werner.

Structural engineers Severud Associates (Manhattan) installed thermocouples in the inner core of concrete slabs and columns of a few floors to measure temperature changes. “After a couple floors, we scrapped the monitoring, because we had proven that we had the proper temperatures. We got the early strengths that were required to maintain a two-day cycle,” says Bob Mannino.

“Our ultimate strengths far exceeded the required design strengths. We were very satisfied with the performance of the slag cement.” Mannino adds that because of its success on this project, Pinnacle Industries now uses between 25 and 30 percent slag cement replacement in all of its mixes for other projects. Mannino also explains, “We’re getting a more consistent quality in terms of early and ultimate strengths”.
 
Project Team:
Owner: The Durst Organization, New York, NY
Owner's Representative: Rose Associates, New York, NY
Architect: Fox & Fowle Associates, New York, NY
Structural Engineer: Severud Associates, New York, NY
Construction Manager: Kreisler Borg Florman, Scarsdale, NY
Concrete Contractor: Pinnacle Industries,Harrison, NY
Concrete Supplier: Empire Transit Mix,Brooklyn, NY
Cement & Slag Supplier: Lehigh Cement,Newark, NJ

Slag Cement Association