HOFFMAN, GRETCHEN K., New Mexico Bureau of Mines and Mineral Resources, Socorro, NM

ABSTRACT: Uses Of Fly Ash From New Mexico Coals

New Mexico's coal mines produced 26.7 million st of coal in 1997. Two-thirds of this tonnage was delivered to three electrical generating stations in New Mexico. All but a small portion of the remaining production is shipped by rail to generating stations in Arizona. New Mexico coals are high in ash content, from 13-27%, creating significant amounts of coal combustion byproducts, most of which is fly ash.

Fly ash is captured from the flue gas after coal combustion by electrostatic or mechanical means. The type of coal, particularly the total silica, alumina, and iron oxides, and the amount of calcium-bearing minerals in the inorganic fraction determine the class of fly ash (C or F). Fly ash is an artificial pozzolan with many characteristics that make it attractive as an admixture to concrete, including strength, lowering heat of hydration, workability, and resistance to alkali-silica reaction. Use of fly ash lowers the cost of the concrete and saves energy by decreasing the amount of cement needed.

Fly ash usage from New Mexico coals is about 44% (1.56 million st) of the total 1997 fly-ash production (3.56 million st). New Mexico coals produce Class F fly ash with high silica and low calcium content. These characteristics make New Mexico fly ash a beneficial admixture for Portland cement and concrete, particularly in the Southwest where alkali-silica reactivity is a problem because of the type of aggregate available.

AAPG Search and Discovery Article #90915©2000 AAPG Rocky Mountain Section, Albuquerque, New Mexico