Lightweight Concrete Used to Help Comcast Center Achieve New Heights

By Bill Wolfe, Norlite Corporation

The Comcast Center is currently the tallest building in City Center Philadelphia. It is the tallest building between New York and Chicago and the11th tallest building in the country. The 58-story building received LEED Gold certification for the building’s core and shell from the United States Green Building Council (USGBC), making it the tallest LEED certified building in the nation. The Robert A.M. Stern Architects designed building, which stands 975 feet and totals 1.25 million square feet, is the Comcast Corporation’s headquarters.

Lightweight concrete (LWC) was utilized in the composite floor decks throughout the structure. One of the major advantages of lowering the density of the concrete on this project is the reduction of the deadload. Typical normal weight concrete weighs approximately 145 pounds per cubic feet as compared to a specified lightweight concrete density of 115 pounds per cubic feet. This reduction of density allows a concrete weight savings of over 20 percent. Additionally thinner slab sections are allowed for lightweight concrete to achieve the same fire ratings of a similar normal weight decks. A reduction in slab thickness from 4 ½ inches for normal weight concrete to a slab thickness from 3 ¼ inches for lightweight concrete when combined with the concrete density savings will reduce the total slab weight by 38 percent. The weight saving on a project this size was incredible. This load reduction often reduces the size of columns, beams, and girders as well as foundations and reinforcing steel saving materials and adding to the sustainability of the project. The reduced slab weight also allows for greater spans thereby improving the overall structural efficiency of the building.

The 35,000 cubic yards of lightweight concrete produced by Action Supply Company was placed by Madison Concrete Construction. The lightweight concrete mix design allowed pumping to the upper floors at an astounding height of over 950 feet.

Construction began in January 2005 with the structure officially opening on June 8, 2008.

  • Owner/Developer: Liberty Property Trust – Malvern, PA
  • Architect: Robert A.M. Stern Architects – New York, NY
  • Associate Architect: Kendall/Heaton Associates
  • Structural Engineer: Thornton Tomasetti – New York, NY
  • Construction Manager: L.F. Driscoll Company – Bala Cynwyd, PA
  • Ready mix supplier: Action Supply Company – Sharon Hill, PA
  • Lightweight Aggregate Producer: Norlite Corporation – Albany, NY