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
Office Buildings | Jun 3, 2024
Insights for working well in a hybrid world
GBBN Principal and Interior Designer Beth Latto, NCIDQ, LEED AP, ID+C, WELL AP, share a few takeaways, insights, and lessons learned from a recent Post Occupancy Evaluation of the firm's Cincinnati, Ohio, office.
Multifamily Housing | Jun 3, 2024
Grassroots groups becoming a force in housing advocacy
A growing movement of grassroots organizing to support new housing construction is having an impact in city halls across the country. Fed up with high housing costs and the commonly hostile reception to new housing proposals, advocacy groups have sprung up in many communities to attend public meetings to speak in support of developments.
MFPRO+ News | Jun 3, 2024
New York’s office to residential conversion program draws interest from 64 owners
New York City’s Office Conversion Accelerator Program has been contacted by the owners of 64 commercial buildings interested in converting their properties to residential use.
MFPRO+ News | Jun 3, 2024
Seattle mayor wants to scale back energy code to spur more housing construction
Seattle’s mayor recently proposed that the city scale back a scheduled revamping of its building energy code to help boost housing production. The proposal would halt an update to the city’s multifamily and commercial building energy code that is scheduled to take effect later this year.
Mass Timber | May 31, 2024
Mass timber a big part of Western Washington University’s net-zero ambitions
Western Washington University, in Bellingham, Wash., 90 miles from Seattle, is in the process of expanding its ABET-accredited programs for electrical engineering, computer engineering and science, and energy science. As part of that process, the university is building Kaiser Borsari Hall, the 54,000-sf new home for those academic disciplines that will include teaching labs, research labs, classrooms, collaborative spaces, and administrative offices.
Construction Costs | May 31, 2024
Despite challenges, 2024 construction material prices continue to stabilize
Gordian’s Q2 2024 Quarterly Construction Cost Insights Report indicates that supply chain issues notwithstanding, many commodities are exhibiting price normalization.
University Buildings | May 30, 2024
Washington University School of Medicine opens one of the world’s largest neuroscience research buildings
In St. Louis’ Cortex Innovation District, Washington University School of Medicine recently opened its new Jeffrey T. Fort Neuroscience Research Building. Designed by CannonDesign and Perkins&Will, the 11-story, 609,000-sf facility is one of the largest neuroscience buildings in the world.
Architects | May 30, 2024
AE firm Goodwyn Mills Cawood merges with Southland Engineering
Architecture and engineering firm Goodwyn Mills Cawood (GMC) is further expanding its services through a strategic merger with engineering firm Southland Engineering in Cartersville, Ga.
K-12 Schools | May 30, 2024
Inclusive design strategies to transform learning spaces
Students with disabilities and those experiencing mental health and behavioral conditions represent a group of the most vulnerable students at risk for failing to connect educationally and socially. Educators and school districts are struggling to accommodate all of these nuanced and, at times, overlapping conditions.
MFPRO+ New Projects | May 29, 2024
Two San Francisco multifamily high rises install onsite water recycling systems
Two high-rise apartment buildings in San Francisco have installed onsite water recycling systems that will reuse a total of 3.9 million gallons of wastewater annually. The recycled water will be used for toilet flushing, cooling towers, and landscape irrigation to significantly reduce water usage in both buildings.
