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Fly Ash Identification
Fly ash is the leftover residue from burning coal. Coal is a main fuel component for producing electric power. As a result, tons of fly ash are produced from the coal burning process. The fly ash can have a variable composition, based on the additives used with the coal, such as oil and flue gases. The produced fly ash has a siliceous, or silica-based, composition that functions similarly to the cement portion of the concrete mixture.
Curing Time
Fly ash slows concrete curing time. The change in curing time depends on the fly ash volume within the concrete mixture. The fly ash addition actually hinders the temperature from rising within a curing concrete mixture. Natural concrete curing involves a heightened temperature from the concrete's components reacting with one another. In fact, more fly ash within the concrete mixture will produce even lower concrete temperatures. The resulting lower concrete temperature slows the curing time.
Advantages
In general, a slower curing time would be considered a disadvantage to the concrete drying process, causing a construction job to last longer than normal. However, a slow curing time aids in finished concrete quality. Concrete will crack less during the curing time, producing a strong final material. In addition, water permeability is reduced since fly ash fills in tiny spaces within the concrete structure to lessen pore size.
Applications
Structural concrete, such as building columns, can use between 15 and 35 percent of fly ash within a concrete mixture, based on cement weight. However, larger concrete projects, like dams, can use up to 70 percent fly ash within the concrete mixture. This large fly ash volume percentage helps strengthen the overall final structure for many years of reliable use.