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
High-rise Construction | Jun 23, 2015
The world's best new skyscrapers for 2015
One World Trade Center and Abu Dhabi's Burj Mohammed Bin Rashid Tower are among the four towers named Best Tall Buildings by the Council on Tall Buildings and Urban Habitat.
Museums | Jun 23, 2015
Moreau Kusunoki's 'art in the city' scheme wins Guggenheim Helsinki design competition
The firm’s design concept makes use of the museum’s site, turning it into a bustling, well-connected waterfront hub.
Architects | Jun 22, 2015
NCARB adopts alternative for certification of foreign architects
The change, effective July 1, 2016, will replace the current BEFA Program’s requirements, eliminating the committee dossier review and the need to document seven years of credentialed practice in a foreign country.
BIM and Information Technology | Jun 21, 2015
11 tips for mastering 3D printing in the AEC world
Early adopters provide first-hand advice on the trials and tribulations of marrying 3D printing with the science of building technology.
Events Facilities | Jun 19, 2015
4 ways convention centers are revamping for the 21st century
Today's convention centers require more flexible spaces, the ability to blend virtual and in-person events, and meaningful sustainability, writes Skanska's Tom Tingle.
Engineers | Jun 18, 2015
Architecture and engineering profit margins deliver third consecutive year of growth
Operating profits of AE firms have reach their highest level since 2009, according to a new report by PSMJ Resources.
Architects | Jun 17, 2015
Starchitects' napkin sketches raise thousands for San Diego’s AIAS chapter
Prominent architects who submitted a total of 23 napkin doodles were Zaha Hadid, Cesar Pelli, Robert Venturi, Massimiliano Fuksas, Thom Mayne, and Bjarke Ingels.
BIM and Information Technology | Jun 16, 2015
What’s next for 3D printing in design and construction?
The 3D printer industry keeps making strides in technology and affordability. Machines can now print with all sorts of powderized materials, from concrete to chocolate.
Office Buildings | Jun 12, 2015
Houston's energy sector keeps office construction humming
Colliers International projects continued expansion this year in its quarterly report on national office market.
Smart Buildings | Jun 11, 2015
Google launches company to improve city living
The search engine giant is yet again diversifying its products. Google has co-created a startup, called Sidewalk Labs, that will focus on “developing innovative technologies to improve cities.”