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 13, 2011
Duke University parking garage driven to LEED certification
People parking their cars inside the new Research Drive garage at Duke University are making history—they’re utilizing the country’s first freestanding LEED-certified parking structure.
| Apr 13, 2011
Red Bull Canada HQ a mix of fluid spaces and high-energy design
The Toronto architecture firm Johnson Chou likes to put a twist on its pared-down interiors, and its work on the headquarters for Red Bull Canada is no exception. The energy drink maker occupies 12,300 sf on the top two floors of a three-story industrial building in Toronto, and the design strategy for its space called for leaving the base building virtually untouched while attention was turned to the interior architecture.
| Apr 13, 2011
Former department store gets new lease on life as MaineHealth HQ
The long-vacant Sears Roebuck building in Portland, Maine, was redeveloped into the corporate headquarters for MaineHealth. Consigli Construction and local firm Harriman Architects + Engineers handled the 14-month fast-track project, transforming the 89,000-sf, four-story facility for just $100/sf.
| Apr 12, 2011
Rutgers students offered choice of food and dining facilities
The Livingston Dining Commons at Rutgers University’s Livingston Campus in New Brunswick, N.J., was designed by Biber Partnership, Summit, N.J., to offer three different dining rooms that connect to a central servery.
| Apr 12, 2011
Retail complex enjoys prime Abu Dhabi location
The Galleria at Sowwah Square in Abu Dhabi will be built in a prime location within Sowwah Island that also includes a five-star Four Seasons Hotel, the healthcare facility Cleveland Clinic Abu Dhabi, and nearly two million sf of Class A office space.
| Apr 12, 2011
Luxury New York high rise adjacent to the High Line
Located adjacent to New York City’s High Line Park, 500 West 23rd Street will offer 111 luxury rental apartments when it opens later this year.
| Apr 12, 2011
College of New Jersey facility will teach teachers how to teach
The College of New Jersey broke ground on its 79,000-sf School of Education building in Ewing, N.J.
| Apr 12, 2011
Mental hospital in Boston redeveloped as healthcare complex
An abandoned state mental health facility in Boston’s prestigious Longwood Medical Area is being transformed into the Mass Mental Health Center, a four-building mixed-use complex that includes a mental health day hospital, a clinical and office building, a medical research facility for Brigham and Women’s Hospital, and a residential facility.
| Apr 12, 2011
Miami courthouse design does justice to children and the environment
Suffolk Construction broke ground recently for the Miami-Dade County Children’s Courthouse, a $328 million project the firm has a 30-month contract to complete.
| Apr 12, 2011
Long-awaited San Francisco center is music to jazz organization’s ears
After 28 years, SFJAZZ is getting its first permanent home. The San Francisco-based nonprofit, which is dedicated to advancing the art of jazz through concerts and educational programs, contracted local design firm Mark Cavagnero Associates and general contractor Hathaway Dinwiddie to create a modern performance center in the city’s Hayes Valley neighborhood