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
Green | Jan 17, 2023
Top 10 U.S. states for green building in 2022
The U.S. Green Building Council (USGBC) released its annual ranking of U.S. states leading the way on green building, with Massachusetts topping the list. The USGBC ranking is based on LEED-certified gross square footage per capita over the past year.
Libraries | Jan 13, 2023
One of the world’s largest new libraries opens in Shanghai
Designed by Schmidt Hammer Lassen Architects, Shanghai Library East covers more than 1.2 million sf, 80% of it dedicated to community activity.
Religious Facilities | Jan 9, 2023
Santiago Calatrava-designed St. Nicholas Greek Orthodox Church opens in New York
In December, New York saw the reopening of the new St. Nicholas Greek Orthodox Church and National Shrine—the only religious structure destroyed on 9/11. Renowned architect and engineer Santiago Calatrava designed St. Nicholas Church to address the traditional Greek Orthodox liturgy while honoring the Church’s connection with the World Trade Center Memorial site.
Government Buildings | Jan 9, 2023
Blackstone, Starwood among real estate giants urging President Biden to repurpose unused federal office space for housing
The Real Estate Roundtable, a group including major real estate firms such as Brookfield Properties, Blackstone, Empire State Realty Trust, Starwood Capital, as well as multiple major banks and CRE professional organizations, recently sent a letter to President Joe Biden on the implications of remote work within the federal government.
Sustainability | Jan 9, 2023
Innovative solutions emerge to address New York’s new greenhouse gas law
New York City’s Local Law 97, an ambitious climate plan that includes fines for owners of large buildings that don’t significantly reduce carbon emissions, has spawned innovations to address the law’s provisions.
Fire and Life Safety | Jan 9, 2023
Why lithium-ion batteries pose fire safety concerns for buildings
Lithium-ion batteries have become the dominant technology in phones, laptops, scooters, electric bikes, electric vehicles, and large-scale battery energy storage facilities. Here’s what you need to know about the fire safety concerns they pose for building owners and occupants.
Market Data | Jan 6, 2023
Nonresidential construction spending rises in November 2022
Spending on nonresidential construction work in the U.S. was up 0.9% in November versus the previous month, and 11.8% versus the previous year, according to the U.S. Census Bureau.
Industry Research | Dec 28, 2022
Following a strong year, design and construction firms view 2023 cautiously
The economy and inflation are the biggest concerns for U.S. architecture, construction, and engineering firms in 2023, according to a recent survey of AEC professionals by the editors of Building Design+Construction.
Performing Arts Centers | Dec 23, 2022
Diller Scofidio + Renfro's renovation of Dallas theater to be ‘faithful reinterpretation’ of Frank Lloyd Wright design
Diller Scofidio + Renfro recently presented plans to restore the Kalita Humphreys Theater at the Dallas Theater Center (DTC) in Dallas. Originally designed by Frank Lloyd Wright, this theater is the only freestanding theater in Wright’s body of work.
University Buildings | Dec 22, 2022
Loyola Marymount University completes a new home for its acclaimed School of Film and Television
California’s Loyola Marymount University (LMU) has completed two new buildings for arts and media education at its Westchester campus. Designed by Skidmore, Owings & Merrill (SOM), the Howard B. Fitzpatrick Pavilion is the new home of the undergraduate School of Film and Television, which is consistently ranked among the nation’s top 10 film schools. Also designed by SOM, the open-air Drollinger Family Stage is an outdoor lecture and performance space.
