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
Office Buildings | Mar 12, 2018
Sound advice on workplace design
Thoughtful design, paired with a change management program to educate staff, can both enhance connectivity and minimize distractions.
Architects | Mar 9, 2018
Designing healthier buildings: Fitwel certification system
The Fitwel certification system is relatively simple and involves registering a building on a custom scorecard.
Architects | Mar 7, 2018
Balkrishna Doshi named 2018 Pritzker Laureate
Over the course of 70 years, Doshi was instrumental in shaping the discourse of architecture throughout India, from low-cost housing for thousands to landmark projects like the Indian Institute of Management.
Architects | Mar 7, 2018
New National Building Museum exhibit explores the architecture of the Manhattan Project
The exhibit will run through March 3, 2019.
Architects | Feb 27, 2018
But first, let me take a selfie: Designing sharable moments
The concept of “selfie walls” has been around for years, but with their growing popularity they have begun to evolve and take on a life of their own.
Market Data | Feb 27, 2018
AIA small firm report: Half of employees have ownership stake in their firm
The American Institute of Architects has released its first-ever Small Firm Compensation Report.
Museums | Feb 26, 2018
*UPDATED* Design team unveils plans for the renovated and expanded Gateway Arch Museum
The goal of the project is to create closer and more robust connections between the Gateway Arch Museum and the landscape of the Jefferson National Expansion Memorial.
Architects | Feb 23, 2018
AIA elevates 152 members and two international architects to the College of Fellows
AIA Fellowship recognizes significant contributions to profession of architecture and society.
Airports | Feb 21, 2018
Terminal Modernization: Why Bother? Part II
This is the second post in our series examining why airport operators should bother to upgrade their facilities, even if capacity isn’t forcing the issue.
Urban Planning | Feb 21, 2018
Leading communities in the Second Machine Age
What exactly is the Second Machine Age? The name refers to a book by MIT researchers Erik Brynjolfsson and Andrew McAfee.