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
| Aug 11, 2010
Gensler, HOK, HDR among the nation's leading reconstruction design firms, according to BD+C's Giants 300 report
A ranking of the Top 100 Reconstruction Design Firms based on Building Design+Construction's 2009 Giants 300 survey. For more Giants 300 rankings, visit http://www.BDCnetwork.com/Giants
| Aug 11, 2010
Gensler, Arup, HOK among the largest office sector design firms
A ranking of the Top 100 Office Design firms based on Building Design+Construction's 2009 Giants 300 survey. For more Giants 300 rankings, visit http://www.BDCnetwork.com/Giants
| Aug 11, 2010
Callison strengthens retail design presence with RYA acquisition
Callison LLC on June 1 acquired RYA Design Consultancy, a Dallas-based retail architecture and design firm with offices in New York City. The new “Callison RYA Studio” will merge staff and clients into Callison ’s existing retail practice at their Dallas and New York offices.
| Aug 11, 2010
Prism-shaped design unveiled for five-star hotel in Saudi Arabia
Goettsch Partners has been commissioned by Saudi Oger Ltd. to design a new five-star, 214-key business hotel in the King Abdullah Financial District in Riyadh, Saudi Arabia. As a design-build assignment, Saudi Oger is serving as the contractor, selected by developer Rayadah Investment Company. The project is sited on Parcel 1.08, one of the first 10 parcels currently under development in the massive new master-planned district.
| Aug 11, 2010
Construction Specifications Institute to end support of MasterFormat 95 on December 31, 2009
The Construction Specifications Institute (CSI) announced that the organization will cease to license and support MasterFormat 95 as of December 31, 2009. The CSI Board of Directors voted to stop licensing and supporting MasterFormat 95 during its June 16, 2009, meeting at the CSI Annual Convention in Indianapolis.
| Aug 11, 2010
Gensler among eight teams named finalists in 'classroom of the future' design competition
Eight teams were recognized today as finalists of the 2009 Open Architecture Challenge: Classroom. Finalists submitted designs ranging from an outdoor classroom for children in inner-city Chicago, learning spaces for the children of salt pan workers in India, safe spaces for youth in Bogota, Colombia and a bamboo classroom in the Himalayan mountains.
| Aug 11, 2010
F&S Partners merges with SmithGroup
F&S Partners, a Dallas architecture firm specializing in the design of educational, recreational, and religious projects, has merged with SmithGroup, a top 10 U.S. architecture/engineering firm. The 40-person office in Dallas will carry the name SmithGroup/F&S.