Proportioning Concrete Mixtures Using Fly Ash
C. E. Lovewell and George W. Washa
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Results of compressive strength tests of concrete are shown comparing concrete mixtures containing Chicago fly ash with mixtures made without fly ash. The straight portland cement mixes contained from 4 to 6 bags of portland cement per cu yd of concrete and varied in half-bag increments. The mixes containing fly ash were proportioned to have approximately the same early strengths as the comparable straight portland cement mixes. To accom-plish this the cement content could not be reduced by more than 1 bag per cu yd of concrete, and the fly ash added had to exceed the amount of cement removed. The amount of fly ash,needed to replace each pound of cement re- moved increased as the richness of the original straight portland cement mix decreased. Data show that existing concrete technology can serve as a guide in proportioning concrete mixtures containing fly ash and that results can be predicted with reasonable accuracy.