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
Smart Buildings | Apr 7, 2023
Carnegie Mellon University's research on advanced building sensors provokes heated controversy
A research project to test next-generation building sensors at Carnegie Mellon University provoked intense debate over the privacy implications of widespread deployment of the devices in a new 90,000-sf building. The light-switch-size devices, capable of measuring 12 types of data including motion and sound, were mounted in more than 300 locations throughout the building.
Affordable Housing | Apr 7, 2023
Florida’s affordable housing law expected to fuel multifamily residential projects
Florida Gov. Ron DeSantis recently signed into law affordable housing legislation that includes $711 million for housing programs and tax breaks for developers. The new law will supersede local governments’ zoning, density, and height requirements.
Energy Efficiency | Apr 7, 2023
Department of Energy makes $1 billion available for states, local governments to upgrade building codes
The U.S. Department of Energy is offering funding to help state and local governments upgrade their building codes to boost energy efficiency. The funding will support improved building codes that reduce carbon emissions and improve energy efficiency, according to DOE.
Steel Buildings | Apr 6, 2023
2023 AISC Forge Prize winner envisions the gas station of the future
Forge Prize winner LVL (Level) Studio envisions a place where motorists can relax, work, play, shop, or perhaps even get healthcare while their vehicles charge.
Architects | Apr 6, 2023
New tool from Perkins&Will will make public health data more accessible to designers and architects
Called PRECEDE, the dashboard is an open-source tool developed by Perkins&Will that draws on federal data to identify and assess community health priorities within the U.S. by location. The firm was recently awarded a $30,000 ASID Foundation Grant to enhance the tool.
Architects | Apr 6, 2023
Design for belonging: An introduction to inclusive design
The foundation of modern, formalized inclusive design can be traced back to the Americans with Disabilities Act (ADA) in 1990. The movement has developed beyond the simple rules outlined by ADA regulations resulting in features like mothers’ rooms, prayer rooms, and inclusive restrooms.
Market Data | Apr 6, 2023
JLL’s 2023 Construction Outlook foresees growth tempered by cost increases
The easing of supply chain snags for some product categories, and the dispensing with global COVID measures, have returned the North American construction sector to a sense of normal. However, that return is proving to be complicated, with the construction industry remaining exceptionally busy at a time when labor and materials cost inflation continues to put pricing pressure on projects, leading to caution in anticipation of a possible downturn. That’s the prognosis of JLL’s just-released 2023 U.S. and Canada Construction Outlook.
Cladding and Facade Systems | Apr 5, 2023
Façade innovation: University of Stuttgart tests a ‘saturated building skin’ for lessening heat islands
HydroSKIN is a façade made with textiles that stores rainwater and uses it later to cool hot building exteriors. The façade innovation consists of an external, multilayered 3D textile that acts as a water collector and evaporator.
Market Data | Apr 4, 2023
Nonresidential construction spending up 0.4% in February 2023
National nonresidential construction spending increased 0.4% in February, according to an Associated Builders and Contractors analysis of data published by the U.S. Census Bureau. On a seasonally adjusted annualized basis, nonresidential spending totaled $982.2 billion for the month, up 16.8% from the previous year.
Sustainability | Apr 4, 2023
ASHRAE releases Building Performance Standards Guide
Building Performance Standards (BPS): A Technical Resource Guide was created to provide a technical basis for policymakers, building owners, practitioners and other stakeholders interested in developing and implementing a BPS policy. The publication is the first in a series of seven guidebooks by ASHRAE on building decarbonization.
