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
| Jan 21, 2011
Upscale apartments offer residents a twist on modern history
The Goodwynn at Town: Brookhaven, a 433,300-sf residential and retail building in DeKalb County, Ga., combines a historic look with modern amenities. Atlanta-based project architect Niles Bolton Associates used contemporary materials in historic patterns and colors on the exterior, while concealing a six-level parking structure on the interior.
| Jan 21, 2011
Research center built for interdisciplinary cooperation
The Jan and Dan Duncan Neurological Research Institute at Texas Children’s Hospital, in Houston, the first basic research institute for childhood neurological diseases, is a 13-story twisting tower in the center of the hospital campus.
| Jan 21, 2011
Music festival’s new home showcases scenic setting
Epstein Joslin Architects, Cambridge, Mass., designed the Shalin Liu Performance Center in Rockport, Mass., to showcase the Rockport Chamber Music Festival, as well at the site’s ocean views.
| Jan 21, 2011
GSA Recognizes the Best in Public Architecture
The U.S. General Services Administration recognized the best in public architecture and civilian federal workplaces at the 2010 GSA Design Awards in Washington, D.C. This year's 11 award winners showcase the federal government's commitment to cutting-edge architectural design and its focus on sustainability.
| Jan 20, 2011
Houston Dynamo soccer team plans new venue
Construction is scheduled to begin this month on a new 22,000-seat Major League Soccer stadium for the Houston Dynamo. The $60 million project is expected to be ready for the 2012 MLS season.
| Jan 20, 2011
Worship center design offers warm and welcoming atmosphere
The Worship Place Studio of local firm Ziegler Cooper Architects designed a new 46,000-sf church complex for the Pare de Sufrir parish in Houston.
| Jan 20, 2011
Construction begins on second St. Louis community center
O’Fallon Park Recreation Complex in St. Louis, designed by local architecture/engineering firm KAI Design & Build, will feature an indoor aquatic park with interactive water play features, a lazy river, water slides, laps lanes, and an outdoor spray and multiuse pool.
| Jan 20, 2011
Community college to prepare next-gen Homeland Security personnel
The College of DuPage, Glen Ellyn, Ill., began work on the Homeland Security Education Center, which will prepare future emergency personnel to tackle terrorist attacks and disasters. The $25 million, 61,100-sf building’s centerpiece will be an immersive interior street lab for urban response simulations.
| Jan 19, 2011
Industrial history museum gets new home in steel plant
The National Museum of Industrial History recently renovated the exterior of a 1913 steel plant in Bethlehem, Pa., to house its new 40,000-sf exhibition space. The museum chose VOA Associates, which is headquartered in Chicago, to complete the design for the exhibit’s interior. The exhibit, which has views of five historic blast furnaces, will feature artifacts from the Smithsonian Institution to illustrate early industrial America.
| Jan 19, 2011
Baltimore mixed-use development combines working, living, and shopping
The Shoppes at McHenry Row, a $117 million mixed-use complex developed by 28 Walker Associates for downtown Baltimore, will include 65,000 sf of office space, 250 apartments, and two parking garages. The 48,000 sf of main street retail space currently is 65% occupied, with space for small shops and a restaurant remaining.
