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 7, 2014
Thom Mayne's high-tech Emerson College LA campus opens in Hollywood [slideshow]
The $85 million, 10-story vertical campus takes the shape of a massive, shimmering aircraft hangar, housing a sculptural, glass-and-aluminum base building.
| Mar 7, 2014
Learning from common leadership errors
As a leader in the AEC world, you’ll likely find yourself making certain mistakes over the course of your career. Here are a few common leadership errors that can easily be avoided.
| Mar 6, 2014
BD+C wants to hear about your breakthrough ideas and projects for the Giants 300 report
BD+C's 2014 Giants 300 survey form is now available. But completing the survey is just one way to participate in the July Giants issue.
| Mar 6, 2014
Must see: Tour Seinfeld's apartment with virtual reality headset
Fans of the show can now explore a virtual 3D model of the iconic New York residence, thanks to one Web designer's painstaking effort.
| Mar 5, 2014
5 tile design trends for 2014
Beveled, geometric, and high-tech patterns are among the hot ceramic tile trends, say tile design experts.
| Mar 4, 2014
How EIFS came to America
Design experts from Hoffmann Architects offer a brief history of exterior insulation and finish systems in the U.S.
| Mar 4, 2014
If there’s no ‘STEM crisis,’ why build more STEM schools?
Before you get your shorts in a knot, I have nothing against science, technology, engineering, or even mathematics; to the contrary, I love all four “STEM” disciplines (I’m lying about the math). But I question whether we need to be building K-12 schools that overly emphasize or are totally devoted to STEM.
| Mar 3, 2014
Negotiate your way to success
There are few business skills as important as negotiation. Many successful businesspeople pride themselves on their ability to turn a deal in their favor. Here are a few key negotiation principles to ensure you’re generally getting a good deal.
| Mar 3, 2014
5 ways to gain clients you actually like
Gaining more clients is one thing. Gaining more clients that you actually like is something else entirely. Here are some tips to perfect the art of attracting and retaining clients that you enjoy working with.
| Mar 3, 2014
Engineering and construction CEOs are cautiously optimistic about the global economy, says PwC
Firm leaders remain leery about the availability of skilled workers, the state of government debt and deficits, and rising material prices, according to PwC’s 2014 Global CEO Survey.