we could easily take the spread to 31 inches, whereas most standard SCC mixes would fall apart at that mark.” To achieve specified perfor- mance goals, the SCC mix for the columns contained a high percentage of cementitious material to control heat gain. As a final step, a demonstration trial was run in a job-site column form to fine-tune the mix and ensure stakeholder expectations were met with flow through and consolidation around the heavily congested reinforcement, strength attainment, and surface finish quality. Work gets underway Construction on the airport project kicked off in January 2016. Six months later, crews were placing pile caps on more than 4,000 pre- stressed, precast concrete piles that were driven 100 feet into sand strata to support the weight of the superstructure. The building’s concrete columns were each supported by four to twelve of these 14-inch-square piles. All of the structural columns were constructed in 20-foot lifts. Work on the exterior perimeter columns started with soil excavation for column placement and then pouring a concrete footing over the pile caps. A rebar cage –assembled horizontally– was then lifted by a crane, placed vertically onto the footing and attached to the footing’s metal starter bars. After cleaning the formwork and applying a release agent to prevent the bonding of concrete to it, crews bolted the two-piece steel formwork around the rebar cage and poured the concrete into the form. The superstructure was designed with a moment-frame system – a hy- brid of steel beams connected to embeds on the concrete columns – to keep the internal spaces of the building as open as possible. Concrete for the internal columns was poured up to the second-floor of the struc- ture and then steel erectors assembled the structural steel. After the deck was put in place, concrete was poured for the second-floor slab and crews worked off the slab to extend the columns up to the third floor. This same work process was followed to extend the columns up to the roof line.
The column rebar cage was placed on a concrete footing poured over four to twelve piles. Photo: Gibbs Construction
Working the terminal and concourses at the same time, the project team required seven cranes on the job site for all the concrete column construction activity. Following a tight production schedule, crews were pouring concrete in 20-foot lifts on four or five columns a day, removing formwork after 12 to 24 hours and starting the next 20-foot lift the next day. Prior to every pour, an independent quality-control laboratory tested the SCC mix to ensure the temperature was below its maximum specified value and that the spread was within the desired range for placement. Six to eight test cylinders were also taken to de- termine 7-day and 28-day strength breaks. The columns were hitting their seven-day strengths in three to four days. A new world-class aerial landmark When the new modern terminal opens in May, it will not only be an example of outstanding design and stellar engineering, but also a trib- ute to all the construction trades in making the architectural vision a reality. Construction of the 350 structural columns took about 12 months and required more than 6,500 cubic yards of the Agileflow concrete to complete. The specified compressive strength on this project was 7,000 psi at 28 days; however, the SCC mix consistently achieved strengths surpassing 11,000 psi. “We are all very proud to have played a role in the successful comple- tion of this magnificent new aerial landmark and the lasting impression it will leave for millions of visitors to the city of New Orleans,” said Lopez. “The superb self-consolidating properties of the advanced SCC product was a great solution to our column production challenges, and the surface finish allowed for the final field finish with minimal rubbing and patching—a huge benefit in terms of time and labor cost savings.”
STEPHEN SALZER (steve.salzer@lafargeholcim.com) is sales manager and DENNIS TRAYLOR (dennis.traylor@lafargeholcim.com) is assistant quality control manager at Lafarge, a member of LafargeHolcim (www.MaterialsThatPerform.com). They can be reached at (504) 834-3341.
All the concrete structural columns for the terminal were constructed in 20-foot lifts. Photo: New Orleans International Airport
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csengineermag.com january 2020
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