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
Healthcare Facilities | Feb 1, 2018
Early supplier engagement provides exceptional project outcomes
Efficient supply chains enable companies to be more competitive in the marketplace.
Industry Research | Jan 30, 2018
AIA’s Kermit Baker: Five signs of an impending upturn in construction spending
Tax reform implications and rebuilding from natural disasters are among the reasons AIA’s Chief Economist is optimistic for 2018 and 2019.
Market Data | Jan 30, 2018
AIA Consensus Forecast: 4.0% growth for nonresidential construction spending in 2018
The commercial office and retail sectors will lead the way in 2018, with a strong bounce back for education and healthcare.
Architects | Jan 29, 2018
14 marketing resolutions AEC firms should make in 2018
As we close out the first month of the New Year, AEC firms have made (and are still making) plans for where and how to spend their marketing time and budgets in 2018.
Education Facilities | Jan 29, 2018
My day as a kindergartner
The idea of a kindergarten-only school presents both challenges and opportunities in regards to the design.
AEC Tech | Jan 29, 2018
thyssenkrupp tests self-driving robot for ‘last mile’ delivery of elevator parts
“With driverless delivery robots, we could fill a gap and get spare parts from our warehouses to the jobsite faster,” said thyssenkrupp SVP Ivo Siebers.
Architects | Jan 26, 2018
Stephen Ayers, FAIA, honored with the 2018 AIA Thomas Jefferson Award
The award honors significant contributions to public architecture.
Architects | Jan 26, 2018
Recipients for the 2018 Collaborative Achievement Award selected
The recipients will be honored at the AIA Conference on Architecture 2018 in New York City.
K-12 Schools | Jan 25, 2018
Cost estimating for K-12 school projects: An invaluable tool for budget management
Clients want to be able to track costs at every stage of a project, and cost estimates (current and life cycle) are valuable planning and design tools, writes LS3P's Ginny Magrath, AIA.
Architects | Jan 25, 2018
Four keys to designing autistic-friendly spaces
Autism, in part, gave us modern architecture, writes PDR’s Julie Troung.