Environmental Purchasing Bulletin #63:
Fly Ash In Concrete

PLEASE NOTE:  These bulletins, published since 1997, are historical.  The content is not updated.

• Introduction
• Fly Ash
  • Benefits
  • Allowance/Specifications
  • Technical Bulletins
• For More Information
• Environmental Purchasing Program

Introduction

Derived from burning coal, fly ash is a valuable additive that makes concrete stronger, more durable and easier to work with. According to the Federal Highway Administration (FHA), the use of fly ash in concrete started in the United States in the early 1930's. The major breakthrough in using fly ash in concrete was the construction of Hungry Horse Dam in 1948, utilizing 120,000 metric tons of fly ash. This decision by the U.S. Bureau of Reclamation paved the way for using fly ash in concrete constructions.

According to the Western Region Ash Group, energy can be saved by reducing the fossil fuel consumption required to produce competing products such as cement, lime and crushed stone, and to mine products such as gypsum, limestone, sand, clay and gravel. For example, each ton of Fly Ash used to replace a ton of cement saves the equivalent of one barrel of oil required to produce the cement. Cement and lime are the third most energy-intensive materials to produce on a per-ton basis, after to steel and aluminum.

Fly Ash

Following is an excerpt from the Western Region Ash Group website: "fly ash is the very small particle mineral residue that results from the burning of powdered coal in utility boilers. The individual particles are very small, like talcum powder, and are carried up and out of the boiler in the flow of exhaust gases leaving the boiler after the coal is consumed. Hence the term " Fly Ash". The Fly Ash particles are removed from the stack gasses using Electrostatic Precipitators, Flue Gas Desulfurization (FGD) systems or Bag Houses and are collected and stored dry for recycling. Fly Ash is a pozzolan: a silica, alumina, and calcium based material which, in the presence of water, will chemically combine with the free lime contained in the fly ash and produces a cementitious material with excellent structural properties. Fly Ash can be used as a direct replacement for portland cement in making concrete, in addition to many other applications." Please check the appropriate specification/standard or your local vendor for the particular application, because percentages of allowable fly ash vary.

Benefits of Using fly ash in concrete:

• Pozzolanic properties reduce need for cement
• Spheres act like ball bearings, increasing workability
• Fills in voids with cementitious material and acts as filler, reducing total surface area to be covered with cement
• Retards heat of hydration; important for large concrete pours (dams, Hibernia oil platform)
• Increased strength with age

Other fly ash uses:

• Road base-substitute for aggregate
• Structural fill-high shear strength, good compaction
• Waste stabilization-solidify into inert mass
• Soil modifier-Aids in compaction, soil density, controls swell potential
• Backfill-Can be poured in place, less time consuming

Allowance/Specifications:

Standards and specifications used in design, and specification documents are maintained in many trade associations and regulatory bodies, according to the specific application. Please follow the links in the "For More Information"; Section to access these specifications or for information how to obtain these specifications, if fees are required.

• American Society of Testing Materials (ASTM)

ASTM C618-00

Standard Specification for Coal Fly Ash and Raw or Calcined Natural Pozzolan for Use as a Mineral Admixture in Concrete

• American Association of State Highway and Transportation Officials (AASHTO)

AASHTO M-295 Use of Fly Ash in Portland Cement Concrete

• Washington State Department of Transportation (WSDOT) 1998 Standard Specifications for Road, Bridge, and Municipal Construction)

9.23.9 Fly Ash

Fly ash shall conform to the requirements of AASHTO M 295 Class C or F including optional chemical requirements as set forth in Table 2 and with a further limitation that the loss on ignition shall be a maximum of 1.5 percent.

Some other areas where fly ash is mentioned:

•  

  2-09.3(1)E Backfilling - Controlled Density Fill

•  

  5-05.3(1)A Alternate Concrete Mix Design for Paving

•  

  6-02.3(2) Proportioning Materials

•  

  6-02.3(2)A Contractor-Provided Mix Design

•  

  9-01.2(4) Blended Hydraulic Cement

   

Technical Bulletins

All of the following bulletins are from the ISG Resources website. Please follow these links, or go to their home page for more information:

Case Study:

Seattle Seahawk Garage & Exhibition Hall

Bulletins:

1. Fly Ash -- Types and Benefits
2. Chemical Comparison of Fly Ash and Portland Cement
3. Strength of Fly Ash Concrete
4. Proportioning Fly Ash Concrete Mixes
5. Fly Ash Improves Workability of Concrete
6. Fly Ash Decreases Permeability of Concrete
7. Fly Ash Increases Resistance to Sulfate Attack
8. Fly Ash Decreases Potential Alkali / Silica Reactivity
9. Fly Ash Increases Resistance to Freezing and Thawing
10. Fly Ash for Structural Concrete
11. Fly Ash for Pumped Concrete
12. Fly Ash for Controlled Density Fill

13. Fly Ash for Concrete Pavement
14. Fly Ash for Pipe Manufacturing
15. Fly Ash for Precast / Prestressed Concrete
16. Fly Ash for Block Manufacturing
17. Fly Ash for Architectural Concrete
18. Fly Ash for Stone Matrix Asphalt
19. Permeability of High-Reactivity Metakaolin Concrete
20. Strength of High Reactivity Metakaolin Concrete

For More Information

Federal Highway Administration (FHA)

Western Region Ash Group

Fly Ash Research Center

American Coal Ash Association

American Society of Testing Materials (ASTM)

American Association of State Highway and Transportation Officials (AASHTO)

Washington State Department of Transportation (WSDOT) Standard Specifications for Road, Bridge, and Municipal Construction (large PDF (Adobe Acrobat) file -- 800 pages):

Local company that sells fly ash:

ISG Resources

Contact: Kent Balcom

Technical Service Representative

951 Industry Drive

Tukwila, WA 98188

Phone: (206)575-2504

Mobile: (206)399-6166

All of the above information is for informational purposes only and In no way should an external link be considered any form of endorsement by King County. Thank you.

The King County Environmental Purchasing Program assists County agencies in implementation of King County Executive Policy CON-7-1-2, which requires agencies to use recycled and other environmentally preferable products wherever practicable.

The program assembles information about these products and makes it available to specific agency users who can evaluate them and develop applications in County projects.

These environmental purchasing bulletins contain information about the results of product evaluations and other accomplishments of County agencies. We hope this information will help you find ways to use recycled materials in the work of your agency and that you will contact us if we can help you with further information or if you have suggestions.