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
| Jun 18, 2013
Report: HVAC occupancy sensors could slash building energy demand by 18%
Researchers at the DOE's Pacific Northwest National Laboratory conclude that significant energy savings can be achieved by varying ventilation levels based on the number of people in a given space.
| Jun 18, 2013
Turner report: Activity in urban markets driving construction cost increases
Turner Construction Company announced that the Second Quarter 2013 Turner Building Cost Index – which measures costs in the non-residential building construction market in the United States – has increased to a value of 859. This reflects a 1.18% increase from the First Quarter 2013 and 4.00% yearly increase from the Second Quarter 2012.
| Jun 17, 2013
First look: Austin to get first high-rise since 2003
Developer Cousins Properties broke ground on the 29-story Colorado Tower in downtown Austin, Texas, the city's first high-rise building since Cousins' completed the Frost Bank Tower a decade ago.
| Jun 17, 2013
DOE launches database on energy performance of 60,000 buildings
The Energy Department today launched a new Buildings Performance Database, the largest free, publicly available database of residential and commercial building energy performance information.
| Jun 14, 2013
First look: Callebaut's eye-popping Möbius building for Taichung arts center
French design firm Vincent Callebaut Architectures has released renderings of "Swallow's Nest," an entry in a design competition for a new cultural center, fine arts museum, and public library in Taichung City, Taiwan. The building, based on a Möbius ring, swirls around a central "Endless Patio."
| Jun 14, 2013
Purdue, industry partners test light steel framing for seismic safety
A partnership of leading earthquake engineering researchers from top U.S. and Canadian universities and design professionals from the steel industry have begun the final phase of a three-year project to increase the seismic safety of buildings that use lightweight cold-formed steel for their primary beams and columns.
| Jun 13, 2013
7 great places that represent excellence in environmental design
An adaptive reuse to create LEED Platinum offices, a park that honors veterans, and a grand national plaza are among the seven projects named winners of the 2013 Great Places Awards. The Environmental Design and Research Association recognize professional and scholarly excellence in environmental design, with special attention paid to the relationship between physical form and human activity or experience.
| Jun 13, 2013
Richard Smith joins Cannon Design Science + Technology practice
Cannon Design, an internationally ranked architectural, engineering and planning firm, is pleased to announce Richard Smith has joined the firm as a Principal. Smith joins the leadership team for Cannon Design’s Science + Technology (S&T) practice and will focus on developing strategies for immediate and long-term growth.
| Jun 13, 2013
Winfrey hired as Health and S&T studio head for SmithGroupJJR Dallas
SmithGroupJJR, one of the nation’s largest architecture, engineering and planning firms, has hired David Winfrey, AIA, LEED AP BD+C, as leader of its Health and Science & Technology Studio at its Dallas, Texas office.
| Jun 13, 2013
WorkingBuildings acquires Specialty Operations Solutions
The WorkingBuildings Companies, a leading provider of comprehensive Owner-based solutions for the built environment, announces the acquisition of Specialty Operations Solutions (SOS), a national provider of research and laboratory services.
