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
Building Team Awards | Apr 10, 2015
Virtual collaboration helps complete a hospital in 24 months
PinnacleHealth needed a new hospital STAT! This team delivered it in two years, start to finish.
Building Team Awards | Apr 10, 2015
New arts venue reinvigorates Virginia Tech's campus
The STV-led Building Team creates a world-class performance and arts venue with learning and entrepreneurial dimensions.
BIM and Information Technology | Apr 9, 2015
A carboard box by Google can bring virtual reality to architecture
The global search engine giant has launched a new product, Google Cardboard, that easily allows users to experience virtual reality.
Building Team Awards | Apr 9, 2015
Multifaced fitness center becomes campus landmark
A sloped running track and open-concept design put this Building Team to the test.
Building Team Awards | Apr 9, 2015
Nation's first LEED-certified bus depot
A bus garage in Harlem shows that even the most mundane of facilities can strut its environmentally sensitive stuff.
Building Team Awards | Apr 9, 2015
Setting the bar for port-of-entry design
Whenever you eat a tomato from Mexico, there’s a one-in-three chance it came through this LEED Gold gateway.
Building Team Awards | Apr 9, 2015
Big D’s billion-dollar baby: New Parkland Hospital Tops the Chart | BD+C
Dallas’s new $1.27 billion public hospital preserves an important civic anchor, Texas-style.
Building Team Awards | Apr 9, 2015
IPD-driven fusion facility serves science and student life in Chicago
In dire need of modern science labs and a student union, North Park University built both—in the same building.
Building Team Awards | Apr 9, 2015
‘Prudent, not opulent’ sets the tone for this Catholic hospital
This Building Team stuck with a project for seven years to get a new hospital built for a faithful client.
Building Team Awards | Apr 9, 2015
9/11 museum triumphs over controversy
The Building Team for this highly visible project had much more than design, engineering, and construction problems to deal with.