Durability Enhancement of Concrete Dams by Controlling and Mitigating AAR Problem

Many concrete dams have suffered from heavy deterioration due to Alkali Aggregate Reaction(AAR).The alkali aggregate reaction occurs between the alkalies in cement paste and reactive minerals in the aggregate produces expansive gel resulting in map cracking and low service life of concrete dams. Researches show that a solution for controlling or mitigating this problem is the usage of appropriate supplementary cementing materials in the mixture design of concretes. This paper discusses the effectiveness of various artificial and natural pozzolans as supplementary cementing materials in controlling AAR expansion for various reactive aggregates. Petrographic examination of aggregates was carried out to determine the types of active minerals. Accelerated mortar bar and concrete prism methods were used to evaluate the reactivity of aggregates. Results of the tests show that for each pozzolan there would be an optimum content to be effective in suppressing AAR expansion in accelerated test method. Results of the long-term prism method show that the expansion is not only related to the type and quantity of the supplementary cementing materials but also depends upon the type and the minerals of the aggregates. However reactivity of some aggregates may be controlled by the optimum content of each pozzolanic materials. It is also concluded that individual evaluation test method may not be suitable for some aggregates and final assessment should be based on different test methods.