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
GIANTS 19 PREMIUM | Dec 23, 2019
Top 90 Sports Facilities Architecture Firms for 2019
Populous, HKS, HOK, Gensler, and HNTB top the rankings of the nation's largest sports facilities sector architecture and architecture engineering (AE) firms, as reported in Building Design+Construction's 2019 Giants 300 Report.
| Dec 18, 2019
Reconsidering construction robotics
After decades when experts predicted that robots would become more prevalent on construction sites, it would appear that the industry has finally reached that point where necessity, aspiration, and investment are colliding.
75 Top Building Products | Dec 16, 2019
Top Window and Door Products for 2019
Pella’s Rolscreen retractable screen and NanaWall’s HSW single-track sliding glass wall are among the 16 window and door products to make Building Design+Construction’s 2019 101 Top Products report.
75 Top Building Products | Dec 16, 2019
Top Structural Products for 2019
Inpro’s Fireline 140 fire barrier and Owens Corning’s Foamglas cellular glass insulation are among the 10 structural products to make Building Design+Construction's 2019 101 Top Products report.
75 Top Building Products | Dec 16, 2019
101 Top Products for 2019
Building Design+Construction readers and editors select their top building products for the past 12 months in the fourth-annual 101 Top Products report.
75 Top Building Products | Dec 16, 2019
Top Plumbing Products for 2019
Sloan's CX Flushometer and Zip Water's HydroTap are among the eight plumbing products to make Building Design+Construction's 2019 101 Top Products report.
75 Top Building Products | Dec 16, 2019
Top Interior Building Products for 2019
Arktura's Delta Drop ceiling and CertainTeed's Decoustics Rondolo wood panels are among the 13 new interior products to make Building Design+Construction's 2019 101 Top Products report.
75 Top Building Products | Dec 16, 2019
Top Glass and Glazing Products for 2019
SageGlass's Harmony dynamic glass and Vitro Architectural Glass's Acuity low-iron glass are among the nine new glass and glazing products to make Building Design+Construction's 2019 101 Top Products report.
75 Top Building Products | Dec 16, 2019
Top Flooring Products for 2019
Tarkett’s aviation-inspired flooring collection and J+J Flooring’s textile composite flooring are among the four new commercial flooring products to make Building Design+Construction’s 2019 101 Top Products report.
75 Top Building Products | Dec 16, 2019
Top Building Systems Products for 2019
FabricAir’s ceiling-hung fabric duct and Ellumi Lighting’s bacteria-killing lights are among the 13 new building systems products to make Building Design+Construction's 2019 101 Top Products report.