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The Three Gorges Dam is famous for being the largest dam throughout the world. Research studies were first conducted in 1984 to investigate the effect of alkali-aggregate reaction (AAR) on the concrete used to construct this dam. The expansion rate of AAR is closely related to the time changes (the time-cumulating effect). The results of AAR were obtained from the observations recorded for a time period of about 20-30years. In this study, we discovered that the expansion rate cumulates as the age extends, and the maximum value of expansion rate can be observed only in certain periods. In particular, the ''peak'' in the curve of expansion rate appears circa in ages 13-16years. Thereafter, the expansion rate of mortar witnessed a declining trend; perhaps, some parts of the long-term mortar containing non-reactive aggregates will undergo a harmful expansion if the alkali content exceeds over 1.20%. Thus, the expansion in this circumstance would be more than 0.1%. However, micro analysis indicates that although the expansion rate of mortar is over 0.1%, no apparent characteristics of AAR are apparent. We could effectively inhibit AAR by adding fly ash and slag. Alumina-oxygen tetrahedron(AlO"4)^5^- was formed, and it rapidly hydrated and intensively absorbed the ions into the gel structure. Once the hydration products attain a high specific surface area in an alkaline medium, the products participating in the reaction involving reactive aggregates of alkali undergo reduction consequently.
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