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
| Nov 29, 2010
Data Centers: Keeping Energy, Security in Check
Power consumption for data centers doubled from 2000 and 2006, and it is anticipated to double again by 2011, making these mission-critical facilities the nation’s largest commercial user of electric power. Major technology companies, notably Hewlett-Packard, Cisco Systems, and International Business Machines, are investing heavily in new data centers. HP, which acquired technology services provider EDS in 2008, announced in June that it would be closing many of its older data centers and would be building new, more highly optimized centers around the world.
| Nov 29, 2010
New Design Concepts for Elementary and Secondary Schools
Hard hit by the economy, new construction in the K-12 sector has slowed considerably over the past year. Yet innovation has continued, along with renovations and expansions. Today, Building Teams are showing a keener focus on sustainable design, as well as ways to improve indoor environmental quality (IEQ), daylighting, and low-maintenance finishes such as flooring.
| Nov 29, 2010
Renovating for Sustainability
Motivated by the prospect of increased property values, reduced utility bills, and an interest in jumping on the sustainability bandwagon, a noted upturn in green building upgrades is helping designers and real estate developers stay busy while waiting for the economy to recover. In fact, many of the larger property management outfits have set up teams to undertake projects seeking LEED for Existing Buildings: Operations & Maintenance (LEED-EBOM, also referred to as LEED-EB), a certification by the U.S. Green Building Council.
| Nov 23, 2010
The George W. Bush Presidential Center, which will house the former president’s library
The George W. Bush Presidential Center, which will house the former president’s library and museum, plus the Bush Institute, is aiming for LEED Platinum. The 226,565-sf center, located at Southern Methodist University, in Dallas, was designed by architect Robert A.M. Stern and landscape architect Michael Van Valkenburgh.
| Nov 23, 2010
Honeywell's School Energy and Environment Survey: 68% of districts delayed or eliminated improvements because of economy
Results of Honeywell's second annual “School Energy and Environment Survey” reveal that almost 90% of school leaders see a direct link between the quality and performance of school facilities, and student achievement. However, districts face several obstacles when it comes to keeping their buildings up to date and well maintained. For example, 68% of school districts have either delayed or eliminated building improvements in response to the economic downturn.
| Nov 16, 2010
Architecture Billings Index: inquiries for new projects remain extremely high
The new projects inquiry index was 61.7, down slightly from a nearly three-year high mark of 62.3 in September, according to the Architecture Billings Index (ABI). However, the ABI dropped nearly two points in October; the October ABI score was 48.7, down from a reading of 50.4 the previous month. The ABI reflects the approximate nine to 12 month lag time between architecture billings and construction spending.
| Nov 16, 2010
Brazil Olympics spurring green construction
Brazil's green building industry will expand in the coming years, spurred by construction of low-impact venues being built for the 2016 Olympics. The International Olympic Committee requires arenas built for the 2016 games in Rio de Janeiro meet international standards for low-carbon emissions and energy efficiency. This has boosted local interest in developing real estate with lower environmental impact than existing buildings. The timing couldn’t be better: the Brazilian government is just beginning its long-term infrastructure expansion program.
| Nov 16, 2010
Green building market grows 50% in two years; Green Outlook 2011 report
The U.S. green building market is up 50% from 2008 to 2010—from $42 billion to $55 billion-$71 billion, according to McGraw-Hill Construction's Green Outlook 2011: Green Trends Driving Growth report. Today, a third of all new nonresidential construction is green; in five years, nonresidential green building activity is expected to triple, representing $120 billion to $145 billion in new construction.
| Nov 16, 2010
Calculating office building performance? Yep, there’s an app for that
123 Zero build is a free tool for calculating the performance of a market-ready carbon-neutral office building design. The app estimates the discounted payback for constructing a zero emissions office building in any U.S. location, including the investment needed for photovoltaics to offset annual carbon emissions, payback calculations, estimated first costs for a highly energy efficient building, photovoltaic costs, discount rates, and user-specified fuel escalation rates.
