Buyer's Guide to Coal Ash-Containing Products

The use of fly ash in concrete is the highest-volume application for fly ash. Bottom ash is also used in concrete, but at a lower rate and primarily as an aggregate.

Fly ash can be used to help overcome customer complaints about "rocky" mixes, "sticky" mixes, "bleeding" mixes, "lean" mixes, and other common problems. It also presents an opportunity for their producer to keep concrete prices competitive with other materials such as wood and asphalt.

Benefits of Using Coal Ash as a Cement Replacement

Concrete requires less water when fly ash is used in place of cement, resulting in less shrinkage and cracking.
Improves water tightness (permeability) and corrosion in concrete.
Easier to place, pump, work, and finish.
Increased acid and sulfate resitance.
Long-term strength gain.
Saves virgin materials, energy, and landfill costs and reduces pollution.

Replacement Rates

Replacement rates of coal fly ash for cement in the production of concrete generally do not exceed 20% to 30%, although coal fly ash-blended cements may range from 0 to 40% coal fly ash by weight, according to American Society for Testing and Materials (ASTM) C 595, for cement Types IP and I (PM). The U.S. Environmental Protection Agency suggests that 15% is a more accepted rate when coal fly ash is used as a partial cement replacement as an admixture in concrete.

It is important to note that many state departments of transportation limit the addition of fly ash to 20% without addressing the issue of optimum performance. Higher additions (40%-60%) of fly ash can generally be used with high-calcium (Class C, or cementitious) fly ash such as those from Powder River Basin coals. Increasing the addition of Class C fly ash from 20% to 40% will generally result in a better-performing concrete. This is NOT true for Class F ashes that are nonreactive and pozzolanic. Generally, a 20% addition of Class F fly ash is optimum.

Availability

Your local concrete supplier can advise you about the best mix for your job. The only way to ensure that fly ash will be used in concrete is by requesting it. For further information, contact:

National Ready Mix Association
900 Spring Street
Silver Spring, MD 20910
Phone: 301-587-1400
888-846-7622
Fax: 301-585-4219
Web Address: www.nrmca.org

Portland Cement Association
5420 Old Orchard Road
Skokie, IL 60077
Phone: 847-966-6200
Fax: 847-966-8389
E-Mail: info@portcement.org
Web Address: www.portcement.org

Agencies desiring a testing or quality assurance program for cements, blended cements, or coal fly ash should contact:

U.S. Army Engineer Waterways Experiment Station
PO Box 631
Vicksburg, MS 39180

EERC • University of North Dakota • 15 N 23rd St • Grand Forks • North Dakota • USA • 58202-9018 • Phone (701) 777-5000 • Fax (701) 777-5181