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
| May 16, 2014
Toyo Ito leads petition to scrap Zaha Hadid's 2020 Olympic Stadium project
Ito and other Japanese architects cite excessive costs, massive size, and the project's potentially negative impact on surrounding public spaces as reasons for nixing Hadid's plan.
| May 15, 2014
Paints, coatings, and sealants: 10 new ways to seal the deal
Color-shifting finishes, dry-erase surfaces, and stain-blocking paints are highlighted in this round up of new offerings in paints, coatings, sealants, and finishes.
| May 15, 2014
Biking to work up by 60 percent, according to Census Bureau report
Many U.S. cities are seeing an increase in bicycle commuters, according to new a U.S. Census Bureau report. While bicyclists still account for just 0.6% of all commuters, some of the nation's largest cities have more than doubled their rates since 2000.
| May 15, 2014
'Virtually indestructible': Utah architect applies thin-shell dome concept for safer schools
At $94 a square foot and "virtually indestructible," some school districts in Utah are opting to build concrete dome schools in lieu of traditional structures.
| May 15, 2014
First look: 9/11 Memorial Museum opens to first-responders, survivors, 9/11 families [slideshow]
The 110,000-sf museum is filled with monumental artifacts from the tragedy and exhibits that honor the lives of every victim of the 2001 and 1993 attacks.
| May 14, 2014
New study shows employees aren't happier working in green buildings
People working in buildings certified under LEED’s green building standard appear no more satisfied with their workplace environments than those in conventional buildings, according to new research from the University of California, Berkeley, and the University of Nottingham.
| May 14, 2014
Construction growth looking up: Gilbane Spring 2014 Economic Report
Construction spending for 2014 should finish 6.6% higher than in 2013, with nonresidential work contributing substantially.
| May 14, 2014
Prefab payback: Mortenson quantifies cost and schedule savings from prefabrication techniques
Value-based cost-benefit analysis of prefab approaches on the firm's 360-bed Exempla Saint Joseph Heritage Project shows significant savings for the Building Team.
| May 13, 2014
First look: Nadel's $1.5 billion Dalian, China, Sports Center
In addition to five major sports venues, the Dalian Sports Center includes a 30-story, 440-room, 5-star Kempinski full-service hotel and conference center and a 40,500-square-meter athletes’ training facility and office building.
| May 13, 2014
Drexel University case study report: Green Globes cheaper, faster than LEED
GBI’s Green Globes certification process is significantly less expensive to conduct and faster to complete than LEED certification, says Drexel prof.
