Relevance and evaluation methods of alkali-aggregate reactions in concrete and their occurrence in Portugal. The contribution of geologic knowledge

Abstract

Alkali-aggregate reactions may be considered one of the more deleterious causes of concrete structures degradation. Their kinectics depend on the reactivity of natural aggregates containing species of reactive aggregates (silicic or dolomitic ones) and on the alkali content of the cement matrix and of the aggregates themselves. The occurrence of such reactions may act as a severe limitation of the structures performance, reason why an adequate evaluation of the geologic materials is highly recommendable for defining the appropriate concrete mixes where those reactions might be avoided and for identifying the causes, the actual effects and the predictable behaviour of structures. This paper deals with some geological aspects, characteristic of Portuguese aggregates, and presents some information on the petrographic and mineralogic identification techniques which are illustrated with results obtained in some studied cases.