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
K-12 Schools | Apr 13, 2023
Creating a sense of place with multipurpose K-12 school buildings
Multipurpose buildings serve multiple program and functional requirements. The issue with many of these spaces is that they tend not to do any one thing well.
Healthcare Facilities | Apr 13, 2023
Urgent care facilities: Intentional design for mental and behavioral healthcare
The emergency department (ED) is the de-facto front door for behavior health crises, and yet these departments are understaffed, overwhelmed, and ill-equipped to navigate the layered complexities of highly demanding physical and behavioral health needs.
Office Buildings | Apr 13, 2023
L.A. headquarters for startup Califia Farms incorporates post-pandemic hybrid workplace design concepts
The new Los Angeles headquarters for fast-growing Califia Farms, a brand of dairy alternative products, was designed by SLAM with the post-Covid hybrid work environment in mind. Located in Maxwell Coffee House, a historic production facility built in 1924 that has become a vibrant mixed-use complex, the office features a café bordered by generous meeting rooms.
Urban Planning | Apr 12, 2023
Watch: Trends in urban design for 2023, with James Corner Field Operations
Isabel Castilla, a Principal Designer with the landscape architecture firm James Corner Field Operations, discusses recent changes in clients' priorities about urban design, with a focus on her firm's recent projects.
3D Printing | Apr 11, 2023
University of Michigan’s DART Laboratory unveils Shell Wall—a concrete wall that’s lightweight and freeform 3D printed
The University of Michigan’s DART Laboratory has unveiled a new product called Shell Wall—which the organization describes as the first lightweight, freeform 3D printed and structurally reinforced concrete wall. The innovative product leverages DART Laboratory’s research and development on the use of 3D-printing technology to build structures that require less concrete.
Market Data | Apr 11, 2023
Construction crane count reaches all-time high in Q1 2023
Toronto, Seattle, Los Angeles, and Denver top the list of U.S/Canadian cities with the greatest number of fixed cranes on construction sites, according to Rider Levett Bucknall's RLB Crane Index for North America for Q1 2023.
University Buildings | Apr 11, 2023
Supersizing higher education: Tracking the rise of mega buildings on university campuses
Mega buildings on higher education campuses aren’t unusual. But what has been different lately is the sheer number of supersized projects that have been in the works over the last 12–15 months.
Architects | Apr 10, 2023
Bill Hellmuth, FAIA, Chairman and CEO of HOK, dies at 69
William (Bill) Hellmuth, FAIA, the Chairman and CEO of HOK, passed away on April 6, 2023, after a long illness. Hellmuth designed dozens of award-winning buildings across the globe, including the Abu Dhabi National Oil Company Headquarters and the U.S. Embassy in Nairobi.
Contractors | Apr 10, 2023
What makes prefabrication work? Factors every construction project should consider
There are many factors requiring careful consideration when determining whether a project is a good fit for prefabrication. JE Dunn’s Brian Burkett breaks down the most important considerations.
Mixed-Use | Apr 7, 2023
New Nashville mixed-use high-rise features curved, stepped massing and wellness focus
Construction recently started on 5 City Blvd, a new 15-story office and mixed-use building in Nashville, Tenn. Located on a uniquely shaped site, the 730,000-sf structure features curved, stepped massing and amenities with a focus on wellness.
