Use of Chicago Fly Ash in Reducing Cement-Aggregate Reaction
C. H. Scholer and G. M. Smith
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The use of 20 to 30 percent Chicago fly ash, by total weight of fly ash plus cement, effectively and economically inhibits certain types of cement-aggregate reaction in concrete. Fly ash, a finely divided dry powder collected by precipitators from flue gases of pulverized coal-burning power plants, forms a cementing medium when it combines with the lime liberated during the hydration of a portland cement. The data presented in this paper refer only to a fly ash obtained from the Chicago area; fly ash from other localities: may not necessarily produce the same results since they are known to vary considerably in chemical and physical properties. Laboratory tests consisted of subjecting 3 x 4 x 16-m. beams to two difierent accelerated exposures to determine cement-aggregate compatibility. These two accelerated exposures have shown an excellent correlation with observed field service records. Cement-aggregate reaction as referred to in this paper is not restricted to the alkali-aggregate reaction, but refers to the physical and perhaps chemical reactions or a combination of both which causes the expansion that is accompanied by "map cracking." Use of fly ash produces concretes similar in nature to concretes with ordinary portland cement, with fly ash concretes showing an increase in workability and improved finishing characteristics.