Abstract: The effects of alkali as different alkali metal ions and as combined with different anions on the hydration characteristics of cement-based materials are reviewed. Besides, in the light of the microstructure and composition of hydration products of cement-based materials, the interaction between alkali and hydration products of cement-based materials are analyzed and compared. The effects of alkali on the hydration characteristics of cement-based materials are different according to different forms of alkali. Alkali changes the structure and composition of cement hydration products, and hydration products in turn absorb hydration products selectively, and thus the cement-based materials exhibit different macro-properties. Moreover, considering the equivalent weight of alkali content as the alkali content in cement-based material is of some deficiencies. Therefore, the effect of the alkali-based form cannot be neglected for the fine control of the performance of cement-based material.

Key words: alkali metal ions, cement-based materials, hydration products, microstructure, anions, forms of existence