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
| Oct 29, 2014
Better guidance for appraising green buildings is steadily emerging
The Appraisal Foundation is striving to improve appraisers’ understanding of green valuation.
| Oct 29, 2014
Increasing number of design projects meeting carbon reduction targets, says AIA report
Of the 2,464 projects accounted for in AIA's 2030 Commitment 2013 Progress Report, 401 are meeting the 60% carbon reduction target—a 200% increase from 2012.
Sponsored | | Oct 29, 2014
What’s the difference between your building’s coating chalking and fading?
While the reasons for chalk and fade are different, both occurrences are something to watch for. SPONSORED CONTENT
Sponsored | | Oct 29, 2014
Historic Washington elementary school incorporates modular design
More and more architects and designers are leveraging modern modular building techniques for expansion projects planned on historical sites. SPONSORED CONTENT
| Oct 29, 2014
Diller Scofidio + Renfro selected to design Olympic Museum in Colorado Springs
The museum is slated for an early 2018 completion, and will include a hall of fame, theater, retail space, and a 20,000-sf hall that will showcase the history of the Olympics and Paralympics.
Smart Buildings | Oct 29, 2014
SCAPE’s 'living breakwaters' resiliency development wins 2014 Buckminster Fuller Challenge
New York-based landscape architecture firm SCAPE won the Buckminster Fuller Institute’s 2014 Fuller Challenge, billed as socially responsible design’s highest award.
| Oct 28, 2014
4 keys to mastering 'design thinking' and the iteration process
When using design thinking and iteration, we’ll sometimes spend multiple days iterating idea after idea, heads down, only to realize we still don’t have it right, writes HDR's Amy Lussetto. She offers tips for success with these idea-nurturing tools.
| Oct 28, 2014
Miami accepts more modest plan to renovate its convention center
The city of Miami has awarded an $11 million contract for its on-again, off-again convention center renovation to Denver-based Fentress Architects, which will serve as the design criteria professional on this project.
| Oct 28, 2014
Kean University creates Michael Graves School of Architecture
Winner of the AIA Gold Medal, the National Medal of the Arts, the Topaz Medallion and the Driehaus Prize for Architecture, Graves is best known for his contemporary building designs and prominent public commissions.
| Oct 27, 2014
Davis, Calif., latest city to join race to develop 'innovation hubs'
The city plans to develop two "innovation centers" with a total of seven million sf of commercial space geared for local research and technology companies.
