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
| Mar 9, 2011
Winners of the 2011 eVolo Skyscraper Competition
Winners of the eVolo 2011 Skyscraper Competition include a high-rise recycling center in New Delhi, India, a dome-like horizontal skyscraper in France that harvests solar energy and collects rainwater, and the Hoover Dam reimagined as an inhabitable skyscraper.
| Mar 9, 2011
Igor Krnajski, SVP with Denihan Hospitality Group, on hotel construction and understanding the industry
Igor Krnajski, SVP for Design and Construction with Denihan Hospitality Group, New York, N.Y., on the state of hotel construction, understanding the hotel operators’ mindset, and where the work is.
| Mar 3, 2011
HDR acquires healthcare design-build firm Cooper Medical
HDR, a global architecture, engineering and consulting firm, acquired Cooper Medical, a firm providing integrated design and construction services for healthcare facilities throughout the U.S. The new alliance, HDR Cooper Medical, will provide a full service design and construction delivery model to healthcare clients.
| Mar 2, 2011
Design professionals grow leery of green promises
Legal claims over sustainability promises vs. performance of certified green buildings are beginning to mount—and so are warnings to A/E/P and environmental consulting firms, according to a ZweigWhite report.
| Mar 2, 2011
Cities of the sky
According to The Wall Street Journal, the Silk Road of the future—from Dubai to Chongqing to Honduras—is taking shape in urban developments based on airport hubs. Welcome to the world of the 'aerotropolis.'
| Mar 2, 2011
How skyscrapers can save the city
Besides making cities more affordable and architecturally interesting, tall buildings are greener than sprawl, and they foster social capital and creativity. Yet some urban planners and preservationists seem to have a misplaced fear of heights that yields damaging restrictions on how tall a building can be. From New York to Paris to Mumbai, there’s a powerful case for building up, not out.
| Mar 1, 2011
Smart cities: getting greener and making money doing it
The Global Green Cities of the 21st Century conference in San Francisco is filled with mayors, architects, academics, consultants, and financial types all struggling to understand the process of building smarter, greener cities on a scale that's practically unimaginable—and make money doing it.
| Mar 1, 2011
How to make rentals more attractive as the American dream evolves, adapts
Roger K. Lewis, architect and professor emeritus of architecture at the University of Maryland, writes in the Washington Post about the rising market demand for rental housing and how Building Teams can make these properties a desirable choice for consumer, not just an economically prudent and necessary one.
| Mar 1, 2011
New survey shows shifts in hospital construction projects
America’s hospitals and health systems are focusing more on renovation or expansion than new construction, according to a new survey conducted by Health Facilities Management magazine and the American Society for Healthcare Engineering (ASHE). In fact, renovation or expansion accounted for 73% of construction projects at hospitals responding to the survey.
| Mar 1, 2011
AIA selects 6 communities for long-term sustainability program
The American Institute of Architects today announced it has selected 6 communities throughout the country to receive technical assistance under the Sustainable Design Assessment Team (SDAT) program in 2011. The communities selected are Shelburne, Vt., Apple Valley, Mn., Pikes Peak Region, Co., Southwest DeKalb County, Ga., Bastrop, Tx., and Santa Rosa, Ca. The SDAT program represents a significant institutional investment by the AIA in public service work to assist communities in developing policy frameworks and long term sustainability plans.
