One of the world’s highest-profile construction projects for 2008 validates high performance concrete as an efficient load-bearing material with the potential
One of the world’s highest-profile construction projects for 2008 validates high performance concrete as an efficient load-bearing material with the potential to offer extraordinary security at a site forever linked to terrorism.
The Freedom Tower at Ground Zero in New York City has begun its ascent out of the massive foundation that was revealed during the post-September 11 World Trade Center site clearing. With a 200-ft.-square footprint Û matching that of each of the original Twin Towers Û the Freedom Tower combines a robust cast-in-place core that will carry loads along with perimeter steel columns.
The core will use high performance concrete mixes with design strengths up to 14,000 psi. New York City’s previous strength benchmark for buildings was a 12,000-psi mix specified for the reinforced concrete Trump World Tower (852 ft., 2001). Main Freedom Tower supplier Quadrozzi Concrete has formulated a family of mixes under the brand iCRETE, all incorporating locally derived Class C fly ash. The company is supplying much material from a Brooklyn plant located less than a mile from the Brooklyn Battery Tunnel, whose lower Manhattan portal is about ∫-mile from the World Trade Center site. A satellite plant in the Maspeth section of Queens will provide back up.
Los Angeles-based proprietors note that iCRETE is an advanced technology that increases quality and performance of ready mixed, and have assisted Quadrozzi Concrete and producers in other markets with mix development and approvals.We were given a tall task to design, test and produce the most extraordinary concrete ever poured in New York City, affirms iCRETE President Tony Arnold. We were able to exceed all tower design specifications. Beyond its engineering benefits for the structure, he adds, iCRETE addresses the project’s environmental goals by using supplementary cementitious materials at factors up to 40 percent.
While the tower is progressing under World Trade Center site owner Port Authority of New York and New Jersey, site lease-holder Silverstein Properties is proceeding with three other high-rise projects in a fast-track effort to replace much of the original building and retail space by 2011-12.