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
| Feb 14, 2012
Thornton Tomasetti names Al Hashimi vice president for its Middle East Operations
Al Hashimi is joining the company to help expand Thornton Tomasetti’s business in the region and support clients locally.
| Feb 13, 2012
WHR Architects renovation of Morristown Memorial Hospital Simon Level 5 awarded LEED Gold
Located in the Simon Building, which serves as the main entrance leading into the Morristown Memorial Hospital campus, the project comprises three patient room wings connected by a centralized nursing station and elevator lobby.
| Feb 13, 2012
Center for Sustainable Building Research launches CommercialWindows.org
Resource aims at reducing commercial operating costs and energy consumption.
| Feb 13, 2012
New medical city unveiled in Abu Dhabi
SOM’s design for the 838-bed, three-million-square foot complex creates a new standard for medical care in the region.
| Feb 10, 2012
Task force addresses questions regarding visually graded Southern Pine lumber
Answers address transition issues, how to obtain similar load-carrying capabilities, and why only some grades and sizes are affected at this time.
| Feb 10, 2012
Atlanta Housing Authority taps Johnson Controls to improve public housing efficiency
Energy-efficiency program to improve 13 senior residential care facilities and save nearly $18 million.
| Feb 10, 2012
Besculides joins New York Office of Perkins Eastman as associate principal
Besculides joins with more than 17 years’ experience in design, business development, and account management for the government, healthcare, and corporate practice areas with a particular focus on the financial and media sectors.
| Feb 10, 2012
Mortenson Construction research identifies healthcare industry and facility design trends
The 2012 Mortenson Construction Healthcare Industry Study includes insights and perspectives regarding government program concerns, the importance of lean operations, flexible facility design, project delivery trends, improving patient experience, and evidence-based design.
| Feb 10, 2012
LAX Central Utility Plant project tops out
Construction workers placed the final structural steel beam atop the Plant, which was designed with strict seismic criteria to help protect the facility and airport utilities during an earthquake.
| Feb 8, 2012
Nauset completes addition and renovation for Winchester senior living community
Theater, library, fitness center, and bistro enhance facility.