When Performance Matters: Advanced Self-Consolidating at Louis Armstrong International Airport
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 Big Easy. 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.
Building a Superstructure: Column Construction Challenges
To optimize the complex geometric design of the iconic 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.
Achieving the Optimal Mix While Avoiding Segregation Challenges
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.
A new world-class aerial landmark
When the new modern terminal opens in May 2019 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.”