Effectiveness of Fly Ash Replacement in the Reduction of Damage due to Alkali-Aggregate Reaction in Concrete

Josef Farbiarz and Ramon L. Carrasquillo


The concrete industry is faced with the urgen need of improving its knowledge about the mechanism by which fly ash helps in the reduction of damage due to alkali-aggregate reaction in concrete to acceptable levels.

The main objective of this research was to identify the most relevant components of fly ash, cement, and concrete aggregates affecting the alkali-aggregate reaction, and to find a relationship between them, indicating type and amount of a given component acceptable for use in concrete to ensure no damage due to alkali-aggregate reaction. The research approach used in this investigation was to conduct a comparative study of the behavior of several mixes made using several aggregate sources in combination with cements with high and low alkali content, and containing different types of fly ash at different replacement percentages.

The variables studied included:
(1) alkali content of the cement,
(2) available alkali content of the fly ash,
(3) degree of alkali reactivity of the aggregate,
(4) type and source of fly ash, and
(5) percentage of cement replaced.

Test results presented in this report are limited to 90-day exposure testing. However, exposure testing of all specimens will continue until the 24-month test age and the results will be included in later reports.

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