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
| Apr 19, 2012
The 10 mistakes most likely to get you sued
The California Chamber of Commerce has produced a white paper cataloging the top 10 mistakes most likely to get a company sued. While a few of the laws cited apply specifically to California, some of them are federal and may apply in your state.
| Apr 19, 2012
Holcim cement plants recognized at PCA Spring Meeting
The Holly Hill plant received the PCA’s Chairman’s Safety Performance Award in recognition of their exceptional health and safety programs. The Theodore plant received the Environmental Performance Award in recognition of the steps they take beyond those required by laws, regulations and permits to minimize their impact on the environment.
| Apr 19, 2012
KTGY Group’s Arista Uptown Apartments in Broomfield, Colo. completed
First of eight buildings highlights unique amenities.
| Apr 19, 2012
Nauset begins work on $20M Joint Forces HQ at Hanscom AFB
3D imaging key to project timetable and cost containment.
| Apr 19, 2012
HBD Construction names Steven Meeks vice president
Meeks will provide expertise for the company in its many diverse areas of construction projects including health care, senior living, education and retail.
| Apr 18, 2012
Lafarge moving North American headquarters to Illinois
Lafarge CEO John Stull says the factors in their decision were location in the Midwest and area transportation.
| Apr 18, 2012
Positive conditions persist for Architecture Billings Index
The AIA reported the March ABI score was 50.4, following a mark of 51.0 in February; greatest demand is for commercial building projects.
| Apr 18, 2012
Syska Hennessy re-launches Information and Communication Technology practice
The ICT practice will focus a blend of products including Information Technology, Security, Audiovisual, Building Automation, Fire Life Safety, Medical Communications and Intelligent Building Systems.
| Apr 18, 2012
Perkins+Will designs new complex for Johns Hopkins Hosptial
The Charlotte R. Bloomberg Children’s Center and the Sheikh Zayed Tower create transformative patient-centric care.
| Apr 18, 2012
BBS Architects & Engineers acquires Ward Associates
The merged companies’ on-going project portfolio valued at $220 million.