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
Sports and Recreational Facilities | Dec 15, 2023
San Antonio Spurs’ new practice facility aims to help players win championships and maintain well-being
Designed by ZGF, the Victory Capital Performance Center uses biophilic design to promote better health and wellness on and off the court.
Affordable Housing | Dec 14, 2023
What's next for affordable housing in 2024?
As 2023 draws to a close, GBBN’s Mary Jo Minerich and Amanda Markovic, AIA sat down to talk about the future. What’s next in terms of trends, technology, and construction of affordable housing?
75 Top Building Products | Dec 13, 2023
75 top building products for 2023
From a bladeless rooftop wind energy system, to a troffer light fixture with built-in continuous visible light disinfection, innovation is plentiful in Building Design+Construction's annual 75 Top Products report.
Giants 400 | Dec 12, 2023
Top 35 Veterans Affairs Facility Architecture Firms for 2023
LEO A DALY, Page Southerland Page, Guidon, and HDR top BD+C's ranking of the nation's largest Veterans Affairs facility architecture and architecture/engineering (AE) firms for 2023, as reported in Building Design+Construction's 2023 Giants 400 Report.
Giants 400 | Dec 12, 2023
Top 40 Military Facility Architecture Firms for 2023
Michael Baker International, HDR, Whitman, Requardt & Associates, and Stantec top BD+C's ranking of the nation's largest military facility architecture and architecture/engineering (AE) firms for 2023, as reported in Building Design+Construction's 2023 Giants 400 Report.
Office Buildings | Dec 12, 2023
Transforming workplaces for employee mental health
Lauren Elliott, Director of Interior Design, Design Collaborative, shares practical tips and strategies for workplace renovation that prioritizes employee mental health.
Giants 400 | Dec 11, 2023
Top 150 Local Government Building Architecture Firms for 2023
Gensler, HOK, Stantec, and Skidmore, Owings & Merrill top BD+C's ranking of the nation's largest local government building architecture and architecture/engineering (AE) firms for 2023, as reported in Building Design+Construction's 2023 Giants 400 Report.
Giants 400 | Dec 11, 2023
Top 90 State Government Building Architecture Firms for 2023
Page Southerland Page, Skidmore, Owings & Merrill, Stantec, and NORR top BD+C's ranking of the nation's largest state government building architecture and architecture/engineering (AE) firms for 2023, as reported in Building Design+Construction's 2023 Giants 400 Report.
Codes and Standards | Dec 11, 2023
Washington state tries new approach to phase out fossil fuels in new construction
After pausing a heat pump mandate earlier this year after a federal court overturned Berkeley, Calif.’s ban on gas appliances in new buildings, Washington state enacted a new code provision that seems poised to achieve the same goal.
Green | Dec 11, 2023
U.S. has tools to meet commercial building sector decarbonization goals early
The U.S. has the tools to reduce commercial building-related emissions to reach target goals in 2029, earlier than what it committed to when it signed the Paris Agreement, according to a report by the U.S. Green Building Council.