Advanced self-consolidating concrete provides the ideal solution to challenges in constructing tall and complex columns at world-class terminal.
By Stephen Salzer and Dennis Traylor
Many things come to mind when people think of New Orleans – the beautiful architecture of the buildings, the vibrancy of the French Quarter and, of course, the landmark Superdome for great sporting events. What they probably don’t picture is a spectacular world-class airport welcoming them to the Big Easy, but that’s exactly what millions of air travelers will soon experience when they visit the Crescent City.
A visionary project of the City of New Orleans, the new terminal at Louis Armstrong New Orleans International Airport will showcase the vibrant spirit and distinct culture of the city. The Hunt-Gibbs-Boh-Metro Joint Venture team was the construction manager of this $1 billion game-changing project, which is one of the most visible symbols of infrastructure rebuilding in the Gulf South region post-Katrina.
The world-class design of the 972,000-square-foot replacement terminal was conceived by Pelli Clarke Pelli Architects and executed by the Crescent City Aviation Team, a joint venture of Leo A. Daly Company and Atkins North America, Inc.
The complex will feature three concourses with 35 passenger gates, seamless connections between concourses, nearly 80,000 square feet of retail space, parking garages and a surface parking lot, and an enormous concrete apron that ties into existing runways.
According to the design team, the terminal’s architectural form evokes the geography of the Delta region and the soft curves of the Mississippi River. The curved, T-shaped building forms a gentle arc on three sides, and a monumental roof rises toward the structure’s centerline where it crests over a large central skylight. Designed to allow long spans, the spherical-shaped roof is supported by massive concrete columns to reflect the region’s modern and upward trajectory.
Construction required an advanced SCC solution to flow through and consolidate around highly congested reinforcement in the columns without the use of vibrators. Photo: New Orleans International Airport
Column construction challenges
To optimize the complex geometric design of the structure, the project team used specialized software to distribute the column grid, optimize the roof shape and right-size the building footprint. They also relied on innovative building materials throughout the project, including an advanced self-consolidating concrete (SCC) to produce the 350 massive support columns for the superstructure. The heights of the 40-inch and 48-inch terminal columns ranged from 47 to 73 feet, and the heights of the 28-inch and 30-inch concourse columns ranged from 33 to 51 feet.
One of the biggest challenges in constructing the tall and complex columns was finding the ideal concrete mix that would perform on a variety of levels. The use of a conventional concrete was not an option for this application due to all the highly congested steel reinforcement, embeds and anchor bolts within the columns. In addition, project specifications required a high-quality class A exposed concrete finish, which would not be possible using a standard concrete mix.
According to Mike Lopez, project superintendent at Gibbs Construction, the project team needed an innovative concrete solution that would flow easily through and firmly self-consolidate around all the highly congested embedded reinforcement within the columns, as well as achieve a 28-day compressive strength of 7,000 psi. The concrete also needed to produce a smooth high-end surface aesthetic that the owner was expecting with every pour.
Selecting the right mix
To meet the stringent performance criteria for this high-vertical application, the project team selected an advanced self-consolidating concrete (SCC), called Agileflow™ (formerly Agilia®). This highly fluid concrete places more quickly than standard concrete, flows easily through highly congested reinforcement and provides superior non-segregation properties for greater structural integrity. Other advantages of the SCC technology include increased strength, higher-quality finished surfaces and reduced production times and labor costs.
“We used this very workable SCC mix provided by Lafarge on another project that had very large transfer beams containing highly congested steel rebar and post-tensioned cables,” said Lopez. “Based on the product’s performance in that extremely challenging application, we were confident that it was the ideal solution for constructing the structural support columns at the airport.”
Based on all the logistics challenges and other delays that come with working on a 100-acre airport construction site, the ability of the product to maintain its workability for up to two hours was another benefit valued by the project team. With most standard SCC mixes, the spread starts to decline tremendously at 1 hour and could cause stability problems.
Following a common defined procedure, Agileflow mixes are custom-designed based on the targeted performance properties for each site-specific application. The key to successful performance requires special care in the selection and proper proportioning of materials in the mix to avoid segregation while providing optimal workability properties.
Primary considerations in developing the optimal concrete for the airport columns were flowability, viscosity, compressive strength, durability, and maximum temperature gain control. Key performance parameters included compressive strength of 7,000 psi at 28 days, maximum temperature of 95 degrees F, and spread of 28 to 31 inches.
“We design our Agileflow advanced SCC mixes to flow at higher capacities and to avoid separation in applications with high drop heights,” said BJ Eckholdt, quality control manager at Lafarge, a member of LafargeHolcim. “With the concrete developed for the airport columns, we could easily take the spread to 31 inches, whereas most standard SCC mixes would fall apart at that mark.” To achieve specified performance 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 prestressed, 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 hybrid 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 structure 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.
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 determine 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 tribute 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 completion 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 (firstname.lastname@example.org) is sales manager and Dennis Traylor (email@example.com) is assistant quality control manager at Lafarge, a member of LafargeHolcim (www.MaterialsThatPerform.com). They can be reached at (504) 834-3341.
*This article was originally published in Civil + Structural Engineer in April 2019