Hartsfield-Jackson Atlanta International is a critical link in the world’s air transportation infrastructure.
During September through November 2006, a 10,000-ft main runway was replaced by GSC Atlanta Inc., a wholly owned subsidiary of Kiewit Southern Co. With a 60-day traffic interruption window, and $225,000 per day in liquidated damages on the line, Kiewit was able to efficiently optimize concrete workflow and monitor concrete quality.
The runway project entailed the removal and replacement of the 10,000-ft-long runway 8R/26L, a 3,500-ft-long taxiway and 14 taxiway/runway approaches. Over 140,000 cu yd of concrete were used to complete the 150-ft-wide and 20-in.-thick pavement. With a 60-day clock ticking, time and resources were critical. Prior to the runway closing, Kiewit was already saw-cutting the runway into panels at night to prepare for rapid removal. Once paving was started, Kiewit was placing up to 8,000 cu yd per day during their 24-hour, seven-day work weeks. At this rate, timely and accurate information for quality control and workflow decisions was critical.
Going down that path
During construction, the Kiewit team was looking for flexural strength targets of:
- 450 psi to drill dowel holes;
- 500 psi to allow construction traffic; and
- 650 psi for air traffic.
The runway was paved in 25-ft-wide lanes averaging 1,600 ft in length. Timing of the doweling operation, which included the drilling and placement of over 60,000 dowels, was critical to allow the rapid placement of adjacent lanes.
“Dowel drilling was our critical path activity,” explained Drueke. “You may spall the edges of the concrete if you drill too early.”
Also, construction traffic needed access to the pavement as soon as possible. “The key to completing the concrete pavement on schedule was achieving the required flexural strength as quickly as possible,” said James Woodward, concrete pavement quality manager for Kiewit Southern Co.
As concrete strength information was needed for optimum timing of these operations, concrete maturity readings were taken and the pavement strength could be determined in real-time.
“If conventional methods were used, the time frame for drilling the dowels would have been approximately 45-55 hours after completion of each lane of pavement and additional hours would be required to allow construction traffic,” explained Woodward.
However, considering the heat generated and trapped in the concrete placement itself, the intelliRock concrete maturity system used indicated the 450 psi flexural strength requirement for drilling was met in only 13-15 hours, far before the two to three days needed to reach strength in the standard-cured beams.
“This saved about 1½ days of wait time for each lane where dowels were required,” Woodward added. “Since $225,000 would be assessed for each day the project was late, the [concrete maturity] system greatly reduced that risk. Overall it is estimated that two to four weeks of construction time were saved by the use of [the concrete maturity system].”
The concrete maturity meter used on the Hartsfield-Jackson Airport project consisted of sensors that were embedded in the concrete placement and a hand-held reader that was used to communicate with the sensors. The information collected by the sensors was stored in the sensor, which was inside the concrete placement where it was protected from construction activities. Instantaneous strength readings could then be taken at any time by reattaching the reader to a sensor in the location of interest and viewing the maturity readings.
“Kiewit introduced this technology to Atlanta’s Department of Aviation (DOA) on a previous project in 2004” said Brian Drueke, project quality manager for Kiewit Southern Co. The DOA has been subsequently experimenting with the technology.
On this project, concrete maturity technology was mandated by the DOA to ensure rapid construction. “We’re constantly looking for innovative technologies that can improve the quality and economics of airport construction,” said Frank Hayes, a consultant to the DOA.
Beam it down
One of the many challenges faced on this project was getting timely information to monitor concrete quality. Since sometimes 10,000+ cu yd of concrete were being placed per day, a considerable amount of concrete was placed before the first traditional beam specimens were broken. Furthermore, 110,000 cu yd was already placed before receiving the first 28-day break. By comparing beam strength information reported by the concrete maturity system with the actual early age strength of the beam specimens, mix quality could be verified within hours of placement. This allowed for a rapid response to strength deviations and rapid feedback from mix design changes, thereby minimizing risk. Rapid QC, along with the additional information provided by intelliRock, resulted in a high level of quality assurance and risk mitigation. Furthermore the project never hit a red light resulting from mix quality issues.
The project originally required seven beams for every 200 cu yd of concrete (750 sets or 5,250 beams); however, based on early trial successes with the concrete maturity system to manage workflow, that number was reduced to one set per 500 cu yd, thereby reducing the number of beams by over 3,000 specimens—a 60% reduction.
Maturity matters
Air traffic was interrupted on midnight on Sept. 8 and resumed the morning of Nov. 6.
“Due to the forethought by the DOA, information from [the concrete maturity system] kept the project on schedule and resulted in substantial savings to both the contractor and owner,” said Woodward.
“We could have completed the job without maturity, but it would have taken major resource adjustments or a change in mix design,” added Drueke. “More cement doesn’t equate to better concrete.”
“From an owner’s perspective, we were happy that we could meet the schedule requirements without adding more cement to the mix,” said Hayes. If workflow decisions would have been based only on traditional beams, the resources needed to complete the project on time, such as staffing and equipment, would have been increased substantially to avoid the $225,000 per day penalty. Also, more expensive concrete would have been needed which would have added $200,000 to the cost of materials.”
