EFFECT OF FLY ASH ON THE AIR-VOID STABILITY OF CONCRETE

Concrete containing both portland cement and fly ash were evaluated to determine the effect of fly ash on air-void stability. Tests indicate that air contents of concrete containing Class C fly ash appear to be more stable than those of concrete containing Class F fly ash. The higher the organic matter content of a fly ash, the higher will be the air-entraining admixture requirement for concrete in which the admixture is used. The higher the air-entraining admixture requirement, the greater is the air loss on extended mixing. Even though the air volume is reduced the spacing factor, specific surface, and number of voids are little affected. The "Foam Index" test was conducted and found to be a satisfactory method for checking air-entraining admixture requirements. (Author)