Ready Mix USA is expected to provide approximately 80,000 cubic yards of ready-mix concrete for the construction of 1105 West Peachtree—a 3.5-acre, multi-use development in midtown Atlanta. The $530 million project got off to a necessarily cool start in mid-2019 when the Cemex USA subsidiary used liquid nitrogen to meet temperature-controlled mix specifications for the foundation.
|In order to avoid unnecessary congestion at Midtown Armour, which is a single central mixed plant, Ready Mix USA staged only one liquid nitrogen tanker (left) at a time.
|Developed by Atlanta-based Selig Enterprises, the 1105 West Peachtree complex will feature three buildings: a 31-story, 660,000-sq.-ft. office tower, a 64-unit luxury condo tower and a 178-room hotel. Completion is scheduled for the second half of 2021.
Since the three-tower complex takes up an entire city block and stands above a mass-transit rail station, it required a unique foundation design with an innovative concrete mixture and pour conditions. The foundation needed nearly 20 transfer girders with varying dimensions, although typically at 7- x 10- x 100-ft. The girders were built using ultra-strong 8,000-psi mass concrete, poured at temperatures below 58° F. Mat foundation placements and beams in elevated floors also required the temperature-controlled mix, resulting in approximately 2,800 cubic yards of concrete with the below 58° F mix specification.
Ready Mix set up two liquid nitrogen stations at its Midtown Armour plant to chill the mass concrete to meet the stringent specifications and deliver each load, which on average were 9 cubic yards/truck, at the correct temperature. Typically, a volume of 50-54 gallons of liquid nitrogen per yard was used to meet the requirement. Careful and frequent temperature monitoring was conducted by Quality Control and Operations staff before and after nitrogen treatment at Midtown Armour, upon arrival at the site, and at the point of discharge, note Ready Mix officials. Overall, 11,000 gallons of nitrogen were consumed per placement, based upon an average volume of 210 cubic yards.
“At Ready Mix USA, we embrace innovation, so our customers get exactly what they need, when they need it,” says Cemex USA Regional President – MidSouth Region Marc Tyson. “With 1105 West Peachtree, we are using state-of-the-art techniques to help develop eye-catching buildings that will be beautiful and functional additions to our community.”