OVERVIEW
Soaring to a height of 1,776 feet (540-meters), the 2.6-million-squarefoot (242,000-square-meter) skyscraper known as One World Trade Center in the lower Manhattan district of New York City is a marvel of design and engineering. Construction of the building, previously called the Freedom Tower, began in April 2006 and at the time was the tallest building in the United States.
The Challenge
Sustainable design was a central theme to One World Trade Center’s development, with the Port Authority of New York/ New Jersey imposing a strict requirement for the replacement of Portland cement with recycled materials. In addition, extremely high performance concrete was necessary to meet the compressive strength requirements of the steel and concrete structural columns, which ranged from 14,000 psi (97 MPa) to 12,000 psi (83 MPa) for the lower 40 floors and 10,000 psi (69 MPa) to 8,600 psi (59 MPa) for the upper floors. The 12,000 psi (83 MPa) concrete phase of the project was the most challenging, with the engineers, owners and contractors all having their own requirements and specifications.
The Results
Through Master Builders Solutions‘ Green Sense Concrete mixture optimization service, Eastern Concrete Materials was able to proportion an EF Technology® concrete mixture with 71% cement replacement. The mixture replaced Portland cement with the recycled materials, non-cementitious fillers and specialized admixtures to exceed all the performance targets specified by the One World Trade Center project stakeholders. This EF Technology mixture was used for the 38,000 yd3 (29,000 m3) of concrete needed for the columns through the first 40 floors. To quantify the environmental impact of sustainable concrete for the structure, an Eco-Efficiency Analysis was conducted, using a methodology validated by NSF International, to compare the specialized EF Technology mixture to a reference mixture. Some practical equivalents for these savings are:
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