October 5, 2026 - Coal fly ash helped engineers build pavement capable of supporting jumbo jets at Newark International Airport in New Jersey, providing a lasting example of how coal combustion byproducts can serve demanding infrastructure applications.

Construction during the early to mid-1970s incorporated fly ash into the foundations beneath runways, taxiways and aircraft aprons. An archived Federal Highway Administration report described Newark as the largest single reported U.S. project using fly ash in pozzolan-stabilized pavement bases at that time.

The agency reported that the pavement sections were still performing satisfactorily after at least 20 years. That finding documents their historical performance rather than establishing their condition today.

Newark International Airport, New Jersey

Photo Credit: James Leynse/Getty Images

A Foundation Designed for Heavy Aircraft

Newark’s pavement system combined an asphalt surface with a substantial supporting base made from lime, Portland cement, fly ash and aggregate.

Engineers constructed the base in three layers, adjusting the mixture between layers. Fly ash accounted for approximately 10% to 12% of the material, while lime and Portland cement together represented 3% to 4%.

The stabilized sections measured between 24 and 36 inches thick. A mixture containing 4% combined lime and Portland cement, along with crushed stone and sand, developed ultimate strengths of approximately 2,000 to 2,600 pounds per square inch.

Those figures illustrate the difference between incorporating coal ash into an engineered structural material and simply using it as loose fill.

How the Material Developed Strength

Fly ash contributes to pavement stabilization through reactions that create a cementitious binder. The resulting matrix holds aggregate particles together and gives the base its load-bearing properties.

FHWA guidance explains that the type of ash matters. Fly ash from bituminous coal generally requires an activating material such as lime or Portland cement. Some ashes from subbituminous coal or lignite have self-cementing characteristics.

Successful construction also requires suitable moisture levels, thorough compaction and controlled curing. Time and temperature affect strength development, while adequate resistance to freezing and thawing is important in colder climates.

Benefits Depend on Careful Engineering

FHWA identifies several potential advantages of fly-ash stabilization, including improved strength and durability, opportunities to use lower-quality aggregates and reduced construction costs.

However, the material requires careful design. Shrinkage can produce cracks in a stabilized base that subsequently extend into the asphalt surface, increasing maintenance needs.

Ash composition, aggregate selection, ingredient proportions and construction practices therefore influence the finished pavement’s performance. Newark’s results do not mean that every source of coal ash will perform equally well.

The airport project demonstrated that properly designed coal-ash mixtures could withstand demanding aircraft loads over many years. It remains a historical example of coal byproducts contributing useful engineering properties to major American transportation infrastructure.