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Fly Ash, Pozzolans, and SCMs

sample image
SEM image of fly ash
from Coronado Generation Station, Arizona
(more about SEM images)

Fly ash is a coal combustion byproduct. New Mexico coals are quite high in ash content so there is a significant amount of ash that is left after burning the coal at a power plant. This material can be used in other products, such as concrete products, soil stabilization, and asphalt products. Not all fly ash is used and that must be disposed of either at the powerplant or taken back to the mine and put in the pits.

Pozzolans are siliceous or siliceous aluminous materials that alone possess little or no cementitious value that will, in a finely divided form and with water, chemically react with cement at ordinary temperatures to form compounds with hydraulic cementitous properties. Supplementary cementitous materials (SCMs) are finely divided, non-crystalline or poorly crystalline materials similar to pozzolans. They possess latent cementing properties that become active in the presence of portland cement and water (Malhotra and Mehta, 1996). Pozzolans can be natural or artificial; primarily artificial pozzolans are those formed as a byproduct of some industrial process such as fly ash, but can include calcined shales and clays. SCMs include ground, granulated blast furnace slag (GGBFS), and high-calcium fly ash. Although Class F fly ash and silica fume are not strictly supplementary cementitious materials, but they are often grouped with GGBFS and Class C fly ash in industry literature as SCMs. Pozzolans and SCMs are called mineral admixtures when added to concrete or blended cements.


  1. Hoffman, G.K., May 2000, Uses of Fly Ash from New Mexico Coals: New Mexico Geology, Vol. 22, No. 2, p. 25-36.
  2. Hoffman, G.K., May 2000, Fly Ash Utilization in the Western United States, 36th Forum on the Geology of Industrial Minerals and 11th Extractive Industry Geology Conference, Bath, England. Abstract
  3. Hoffman, G.K., 2002, Fly Ash utilization in the Western United States: In Scott, P.W., and Bristow, C.M., eds., Industrial Minerals and Extractive Industry Geology: The Geological Society, London, p. 331-339
  4. Hoffman, G.K., 2006, Pozzolans and Supplementary Cementitious Materials: in Kogel, JE. Trivedi, NC., Barker, J.M., and Krukowski, S.T., eds., .Industrial Minerals and Rocks 7th Edition, Society for Mining, Metallurgy and Exploration, Inc., Littleton, CO,  p.
  5. Hoffman, G., May 2007, Environmental and economic factors influencing use of mineral admixtures in concrete over the last 25 years: Proceedings of the 43rd Forum on the Geology of Industrial Minerals 2007: Colorado Geological Survey, Resource Series 46 p.301-322.. Abstract
  6. Hoffman, G.K., March 2009, Factors Influencing use of Mineral Admixtures for the past decade in the Western US, SME Annual Meeting, Denver, CO, preprint 09-081.