Common Uses of Fly Ash

Historical Uses of Fly Ash

  • The Ancient Romans added volcanic ash to concrete to strengthen structures such as the Roman Pantheon and the Coliseum which are both still standing today.
  • The first major use of fly ash in concrete in the United States was used to repair a tunnel at the Hoover Dam in 1942.
  • The Hungry Horse Dam, one of the largest structures in the country was constructed starting in 1948 with concrete containing fly ash.
  • The Ronald Reagan Building and the International Trade Center in Washington, DC, were both built with concrete containing fly ash.


Fly ash has been used around the world as an ingredient in concrete for more than 60 years. Concrete is a construction material consisting primarily of aggregates, Portland cement, and water.

Fly ash can be used to create superior concrete products because of its cementitious properties. Mixing fly ash with Portland cement mixtures can produce stronger and longer lasting roads and bridges than concrete made with only Portland cement as the binder (glue). Fly ash commonly offsets 15-30% of Portland cement in concrete and even higher rates in certain application.

Advantages of using fly ash in concrete:

Improved workability of concrete due to the nature and shape of the ash particles

  • Reduced water demand
  • Reduced bleeding at the edges of pavement
  • Increased ultimate strength of the concrete
  • Reduced permeability to moisture, improving long-term durability of the concrete
  • Decreased heat of hydration during concrete curing
  • Greater concrete resistance to various forms of deterioration
  • Reduced concrete shrinkage



 Fly ash can be used as a borrow material for highway embankments. When fly ash is compacted, a structural fill can be constructed that can support highways.

 Advantages of using fly ash in embankments:

  •  Elimination of the need to purchase, permit, and operate a borrow pit
  • Placement over low-bearing-strength soils
  • Ease of handling and compaction, which reduces construction time and equipment costs


Flowable Fill

 Flowable fill is a material that flows like a liquid, is self-leveling, requires no compaction or vibration to achieve maximum density, hardens to a predetermined strength, and is sometimes used as a controlled low-strength material. When it is made with coal fly ash it can be used in place of conventional backfill materials and alleviates problems and restrictions generally associated with the placement of those materials.

 Advantages of using fly ash in flowable fill:

  •  Placement in any weather, including freezing conditions
  • 100 percent density with no compactive effort
  • Ability to fill around and under structures inaccessible to conventional fill placement techniques
  • Increased soil-bearing capacity
  • Prevention of post-fill settlement problems
  • Increased speed and ease of backfilling operations
  • Decreased variability in the density of backfilled matierals
  • Improved on-the-job safety and reduced labor and excavation costs
  • Easy excavation later when properly designed


Stabilized Road Base Course

 Fly ash and lime can be combined with aggregate to produce a quality stabilized road base course. These road bases are referred to as pozzolanic-stabilized mixtures and are advantageous over other base materials because they provide:

  •  A strong durable mixture
  • Reduced costs
  • Autogenous healing
  • Increased energy efficiency


Asphalt Pavements

 Fly ash also can be used as a mineral filler in asphalt pavements. Mineral fillers increase the stiffness of the asphalt mortar mix, improve the rutting resistance of pavements, and improve the durability of the mix.

 Advantages of using fly ash in asphalt pavements:

  •  Reduced potential for asphalt stripping
  • Reduced cost compared to other mineral fillers

Grouts for Pavement Subsealing

 Grouts for pavement subsealing are proportioned mixtures of fly ash, water, and other materials used to fill voids under a pavement system without raising the slabs by drilling and injecting grout under specified areas of the pavement.

 Advantages of using fly ash in grouts for pavement subsealing:

  •  Quick correction of concrete pavements
  • Minimal traffic disturbance
  • Development of high ultimate strength


Concrete Blocks

 Fly ash can replace sand in autoclaved aerated concrete blocks, a puffed type of solid concrete block already used widely for building construction throughout Europe and Asia. AAC blocks can contain as much as 70% ash and are lightweight and strong, although they can be cut with a saw and hold nails. They are also fire and creep resistant and have good insulating properties for both heat and sound. As American timber resources dwindle and become more expensive, AAC is expected to become a prevalent commercial building material in the United States.


 Recently, fly ash has been used as an ingredient in “ashalloys” a blend of ash and lightweight metals such as aluminum and magnesium. Ashalloy castings are advantageous in weight and cost sensitive products such as automobiles and trucks. Currently companies are developing an ashalloy that would displace some of the lead in lead-acid batteries with fly ash. Such a lead ashalloy would lighten batteries by 50% expanding their usefulness in electric vehicles by increasing acceleration and range. It would also reduce environmental effects associated with the use of lead.


Use of Fly Ash Based on American Coal Ash Association 2004