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
Architects | Jan 4, 2017
The making of visible experts: A path for seller-doers in the AEC industry
Exceptional seller-doers have the ability to ask the right questions, and more importantly, listen.
Building Team | Jan 3, 2017
How does your firm’s hit rate stack up to the AEC competition?
If your firm is not converting at least a third of project proposals when competing for new work, it may be time to reassess your marketing tactics and processes.
Architects | Dec 9, 2016
Leddy Maytum Stacy Architects receives the 2017 AIA Architecture Firm Award
LMSA is the 54th AIA Architecture Firm Award recipient.
| Dec 8, 2016
Paul Revere Williams, FAIA, awarded 2017 AIA Gold Medal
The Gold Medal honors an individual whose significant body of work has had a lasting influence on the theory and practice of architecture.
Building Team | Dec 8, 2016
The NYC Public Design Commission recognizes 12 projects with its 2016 Excellence in Design Award
2016 marked the 34th year the Public Design Commission has handed out its Excellence in Design Awards.
Education Facilities | Dec 7, 2016
How corporate design keeps educational design relevant
Learning is a lot like working; it varies daily, ranges from individual to collaborative, formal to informal and from hands on to digital.
| Dec 6, 2016
Workplace pilots: Test. Learn. Build
Differentiated from mock-ups or beta sites, workplace pilots are small scale built work environments, where an organization’s employees permanently reside and work on a daily basis.
Building Team | Dec 2, 2016
Alexandria Real Estate Equities becomes first real estate investment trust to be named a First-in-Class Fitwel Champion
Fitwel building certification was developed to foster positive impacts on building occupant health and productivity through improvements to workplace design and policies.
Government Buildings | Dec 1, 2016
Unlocking innovation in the government workplace
Government work settings ranked the lowest in their effectiveness across the four work modes: focus (individual) work, collaboration, socializing (informal gathering that fosters trust and teamwork) and learning.
Architects | Nov 20, 2016
D.C.’s first distillery-eatery taps into a growing trend
The stylish location targets customers craving craft spirits and late-night dining.
