President, Dunstan Laboratories, Inc., Denver, Colo
Concrete aggregates may contain reactive constituents that will react with alkalies in cement causing disruptive expansions. Concrete deterioration caused by alkali-aggregate reaction can be prevented by using nonreactive aggregate or using cement with sufficiently low alkali content. However, energy conservation and pollution controls can be expected to indirectly increase the alkali content of some cements. On the other hand, the availability of nonreactive aggregate is continually reduced. Other preventive techniques, such as the use of pozzolan admixtures, can be used. But pozzolans vary in their effectiveness in reducing alkali-aggregate reactions. This paper discusses the use of fly ash pozzolan, a finely divided material collected from the exhaust flues of coal-burning power plants, to reduce alkali-aggregate reaction. The effectiveness of fly ash to reduce this reaction appears to depend, in part, on the chemical composition of the fly ash and also on the percent weight replacement of cement by fly ash.
Paper ID: CCA10212J