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
| Mar 6, 2012
Joliet Junior College achieves LEED Gold
With construction managed by Gilbane Building Company, Joliet Junior College’s Facility Services Building combines high-performance technologies with sustainable materials to meet aggressive energy efficiency goals.
| Mar 5, 2012
Tishman constructing new courthouse in Philadelphia
Construction is underway for the Pennsylvania Department of General Services’ 510,000-sf facility.
| Mar 5, 2012
Perkins Eastman pegs O’Donnell to lead K-12 practice
O’Donnell will continue the leadership and tradition of creative design established by firm Chairman and CEO Bradford Perkins FAIA, MRAIC, AICP in leading this market sector across the firm’s 13 offices domestically and internationally.
| Mar 5, 2012
Moody+Nolan designs sustainable fire station in Cincinnati
Cincinnati fire station achieves LEED Gold certification.
| Mar 5, 2012
Gilbane Building Co. wins top honors at ASA Houston awards ceremony
Gilbane was also named General Contractor of the Year for the seventh time in 11 years and won the inaugural Safety Program of the Year award.
| Mar 5, 2012
Franklin Institute in Philadelphia selects Skanska to construct new pavilion
The building has been designed by SaylorGregg Architects and will apply for LEED Silver certification.
| Mar 2, 2012
By the Numbers
66 skyscrapers to built in China over six years; 1,000 questions in the Modern Architecture game; 21,000 new jobs.
| Mar 1, 2012
Intelligent construction photography, not just pretty pictures
Our expert tells how to organize construction progress photos so you don’t lose track of all the valuable information they contain.
| Mar 1, 2012
AIA: A clear difference, new developments in load-bearing glass
Earn 1.0 AIA/CES learning units by studying this article and successfully completing the online exam.
