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
Giants 400 | Aug 26, 2021
2021 University Giants: Top architecture, engineering, and construction firms in the higher education sector
Gensler, AECOM, Turner Construction, and CannonDesign head BD+C's rankings of the nation's largest university sector architecture, engineering, and construction firms, as reported in the 2021 Giants 400 Report.
Giants 400 | Aug 26, 2021
2021 Data Center Giants: Top architecture, engineering, and construction firms in the U.S. data center facilities sector
Corgan, Holder Construction, Jacobs, and Whiting-Turner top BD+C's rankings of the nation's largest data center facilities sector architecture, engineering, and construction firms, as reported in the 2021 Giants 400 Report.
Hotel Facilities | Aug 26, 2021
Building hotels with modules, with citizenM's Menno Hilberts
In this exclusive interview for HorizonTV, Menno Hilberts, Managing Director of Project Management with hotelier citizenM, explains how the company is employing modular construction to help double its presence in the U.S.
Giants 400 | Aug 25, 2021
Top 40 Engineering/Architecture Firms for 2021
Jacobs, AECOM, Burns & McDonnell, and Alfa Tech top the rankings of the nation's largest engineering architecture (EA) firms for nonresidential buildings and multifamily buildings work, as reported in Building Design+Construction's 2021 Giants 400 Report.
Giants 400 | Aug 25, 2021
Top 95 Architecture/Engineering Firms for 2021
Stantec, HDR, HOK, and SOM top the rankings of the nation's largest architecture engineering (AE) firms for nonresidential and multifamily buildings work, as reported in Building Design+Construction's 2021 Giants 400 Report.
Giants 400 | Aug 25, 2021
Top 160 Architecture Firms for 2021
Gensler, Perkins and Will, HKS, and Perkins Eastman top the rankings of the nation's largest architecture firms for nonresidential and multifamily buildings work, as reported in Building Design+Construction's 2021 Giants 400 Report.
Sports and Recreational Facilities | Aug 25, 2021
The rise of entertainment districts and the inside-out stadium
Fiserv Forum, home to the 2021 NBA Champion Milwaukee Bucks, proved that the design of the space outside a stadium is just as important as inside.
Architects | Aug 24, 2021
AIA’s Compensation Report reveals how architecture firms weathered the pandemic
According to the report, architecture firms lost 16,000 positions between February and their low in July of 2020.
Architects | Aug 19, 2021
BD+C Events
Building Design+Construction's annual events include the Women in Design+Construction conference and the ProConnect meeting series.
Architects | Aug 19, 2021
Quattrocchi Kwok Architects marks 35 years in business with commitment to social justice
QKA, the largest architecture firm in the North Bay area of San Francisco, has received the JUST 2.0 Social Transparency Label from the International Living Future Institute.