Airport Revitalization with Portland-Limestone Cement Concrete:
A Foundation of Strength

After a long service life, taxiways at the airport needed rehabilitation, partly due to the cracking from alkali-silica reaction, or ASR. The airport authority, in their role as owners, collaborated with the designer to opt for concrete as the ideal choice for a multitude of practical reasons. Concrete stood out due to its exceptional long-term durability, capacity to endure heavy equipment traffic, and resilience against challenging exposure conditions, including freezing temperatures and deicer applications.

​

Lighter Traffic Volume, Heavy-Duty Pavement

​

Even regional airports such as SPI require heavy-duty pavements to carry traffic from airplanes and other large, heavy equipment. The combination of pavement thickness and concrete strength make it possible to support heavy loads without cracking. For the taxiway rehabilitation project at SPI, designers selected a pavement thickness of 17.5 inches. Rather than a compressive strength, they specified a 28-day modulus of elasticity (E) of 6.5 million psi. 
 

Generally, a higher E is correlated to a higher compressive strength, but it’s the higher modulus of elasticity that helps concrete resist cracking as it carries heavy rolling traffic loads. Rigid pavements, such as concrete, excel in their ability to efficiently distribute loads across a broader surface area compared to flexible pavements. Additionally, the strength and thickness of these robust pavements alleviate pressure on the subgrade, resulting in enhanced pavement longevity.
 

Exposure conditions were a major factor when designing the concrete mix for these taxiways. A moderately low water to cement ratio of 0.40 and 6% air content increase durability, especially for freeze-thaw and deicer exposures. This resulted in a fairly stiff mixture, so a water reducer was beneficial to workability and achieving a 2- to 3-inch slump that works well with conveyors for moving concrete into place. The 20% fly ash content helps protect against ASR deterioration.

Smooth Operations, Compact Construction Schedule 

​

By airport standards, this project required a rather modest 45,000 square feet of pavement. The concrete placement took just 48 hours, and the overall project was completed in one month. The early fall weather was nearly ideal for concrete work: 70 to 80 degrees Fahrenheit and a relative humidity of 40% to 60%. Light winds were no problem as the membrane-forming curing compounds helped prevent evaporation from the freshly placed pavement.
 

Like the portland cement it replaced, the portland-limestone cement was compatible with the concrete mix design parameters and requirements for mixture handling and placing methods. It was compatible with the necessary admixtures, allowed for the use of fly ash for ASR resistance, and as an extra benefit, it reduced the carbon footprint of this project immensely. PLC lowers the carbon footprint by up to 10% compared to portland cement. Replacing portland cement with PLC for the 2500 cu yd of concrete needed to rebuild these taxiways is estimated to have saved about 42 metric tons of CO2.