Soaring to a height of 1,776 feet (540-meter), the 2.6-million-sf (242,000-square-meter) building soon to become the new 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 dubbed the Freedom Tower, began in April 2006 and, when it is completed in 2013, it will be the tallest building in the U.S.
The building will feature an expansive public lobby, a series of mechanical floors, followed by 69 office floors that will include two television broadcast floors, mechanical floors and two restaurants. There will be an observation deck and parapet above these floors, and at the crown, a communications platform and a 408-foot (125-meter), cable-stayed antenna. Below-ground, concourses will offer 55,000-sf (5,100 square-meters) of retail space.
Sustainable design is central to One World Trade Center's development, integrating renewable energy, interior daylighting, reuse of rainwater and of recycled construction debris and materials. But one of the most sustainable elements of the structure is so integral to the mammoth skyscraper’s strength and durability that it might surprise you.
Concrete
The structural columns of One World Trade Center are comprised of steel and concrete. The compressive strength of concrete for these columns is divided into four phases starting at 14,000 psi (97 MPa) at the bottom of the building, and progressing through 12,000 psi (83 MPa), 10,000 psi (69 MPa) and 8,600 psi (59 MPa) to the top. The 12,000 psi (83 MPa) concrete phase of the project was extremely challenging, with the engineers, owners and contractors all having their own requirements and specifications.
Engineering requirements:
- Compressive strength: 12,000 psi (83 MPa) @ 56 days
- Over-design for safety: 1,900 psi (13 MPa)
- Modulus of elasticity: 7.0 million psi (48 GPa)
- Heat of hydration: Not to exceed 160 OF (70 OC)
- Non-air-entrained
Port Authority of New York/New Jersey:
- Quantity of portland cement in the mixture: Less than 400 lb/yd3 (240 kg/m3)
Contractor requirements:
- Slump flow: 22 – 26 inches (560 - 660 mm)
- Ability to pump to at least 40 floors
- No loss in concrete workability during transit and placement
- Aesthetically pleasing
To achieve the desired concrete properties, concrete producer Eastern Concrete Materials, Elmwood Park, N.J. and admixture supplier BASF Construction Chemicals, Beachwood, Ohio, partnered to develop a special high-strength, sustainable concrete mixture. This mixture was used for the 38,000 yd3 (29,000 m3) of concrete needed for the columns through the first 40 floors.
One of the biggest challenges in developing this concrete mixture was meeting the Port Authority of New York/New Jersey’s strict requirement for the replacement of cement. Through BASF’s Green Sense Concrete mixture optimization service, Eastern Concrete Materials was able to proportion a concrete mixture that met this requirement and allowed for the use of high levels of recycled materials. The mixture substantially replaced portland cement with the recycled materials, as well as silica fume, non-cementitious fillers and Glenium high-range water-reducing admixtures to exceed all the performance targets specified by the One World Trade Center project stakeholders.
To determine the environmental impact, an Eco-Efficiency Analysis of the concrete mixture was conducted, using a methodology validated by NSF International, to compare the specialized Green Sense Concrete mixture to a reference mixture. The results of this cradle-to-gate analyses included fresh water savings of 30,492 gallons (115,400 liters), energy savings of over 8 million kWh, air emissions savings of 12 million lb (5445 tonnes) of CO2, solid emissions savings of over 400,000 lb (180 tonnes) and fossil fuel savings of 750,000 lb (340 tonnes).
“We are extremely proud to be part of this historic and iconic project,” said John Salvatore, Head of BASF Construction Chemicals Americas. “But we are especially proud of the collaboration and innovation that was brought to bear in order to make a significant contribution to the enhanced sustainability of One World Trade Center.”
For more on innovative admixtures, click here to visit BASF Admixture Systems. +
Related Stories
Codes and Standards | Mar 2, 2015
Proposed energy standard for data centers, telecom buildings open for public comment
The intent of ASHRAE Standard 90.4P is to create a performance-based approach that would be more flexible and accommodating of innovative change.
K-12 Schools | Mar 1, 2015
Are energy management systems too complex for school facility staffs?
When school districts demand the latest and greatest, they need to think about how those choices will impact the district’s facilities employees.
Office Buildings | Mar 1, 2015
Google unveils dramatic tent-like, modular-focused plan for corporate HQ
The master plan by Bjarke Ingels and Thomas Heatherwick will wrap highly flexible office blocks in soaring translucent canopies.
Industrial Facilities | Feb 27, 2015
Massive windmill will double as mixed-use entertainment tower in Rotterdam
The 571-foot structure will house apartments, a hotel, restaurants, even a roller coaster.
Architects | Feb 27, 2015
5 finalists announced for 2015 Mies van der Rohe Award
Bjarke Ingels' Danish Maritime Museum and the Ravensburg Art Museum by Lederer Ragnarsdóttir Oei are among the five projects vying for the award.
Office Buildings | Feb 26, 2015
Using active design techniques to strengthen the corporate workplace and enhance employee wellness
The new Lentz Public Health Center in Nashville, Tenn., serves as a model of how those progressive and healthy changes can be made.
K-12 Schools | Feb 26, 2015
Should your next school project include a safe room?
Many school districts continue to resist mandating the inclusion of safe rooms or storm shelters in new and existing buildings. But that may be changing.
K-12 Schools | Feb 26, 2015
Construction funding still scarce for many school districts
Many districts are struggling to have new construction and renovation keep pace with student population growth.
K-12 Schools | Feb 26, 2015
D.C.'s Dunbar High School is world's highest-scoring LEED school, earns 91% of base credits
The 280,000-sf school achieved 91 points, out of 100 base points possible for LEED, making it the highest-scoring school in the world certified under USGBC’s LEED for Schools-New Construction system.
K-12 Schools | Feb 25, 2015
Polish architect designs modular ‘kids city’ kindergarten using shipping container frames
Forget the retrofit of a shipping container into a building for one moment. Designboom showcases the plans of Polish architect Adam Wiercinski to use just the recycled frames of containers to construct a “kids city.”
