Taking advantage of innovative construction materials, the 104-story, 1,776-ft. One World Trade Center tower is designed to be the safest and most environmentally friendly commercial building in the world, according to Lafarge.
The structure includes a massive cast-in-place, reinforced concrete inner core that runs the full height of the tower–an extra-strong backbone that provides support for gravitational loads as well as resistance to wind and seismic forces. The concrete core walls measure three feet thick or more above ground and up to twice that below grade. Higher up, the concrete core walls slim down to 2-ft. thick.
The 200,000 cu. yd. of concrete used in the tower's superstructure – with a strength that has never been used on such a scale in building construction – was custom-designed to ensure high levels of durability, constructability and sustainability, notes the company. Supporting columns on the first 40 floors were made from 12,000- to 14,000-psi self-consolidating concrete and the upper floors with 8,600- to 10,000-psi mix designs.
To meet the compressive strength requirements, the design and engineering team relied on a highly specialized concrete mix that included Lafarge Portland Type I/II and NewCem slag cements, as well as other supplementary cementitious materials. Engineered for high strength and long-term durability, NewCem slag cement helps achieve greater strength potential and helps control shrinkage, creep and cracking in mass concrete structures.
High-strength concrete was the ideal material for meeting the high-priority safety requirements for One World Trade Center because key supporting members-such as elevator and stair enclosures-often relied upon to resist wind, seismic and other impact forces, are designed with an extra measure of durability and resilience.
The concrete also made a strong contribution to the sustainable design of the building, which is expected to receive LEED Gold certification when it opens later this year. In addition, the tower was constructed with mostly post-industrial recycled materials, including the NewCem slag cement, which is a by-product of the steel-making process.