Impact of chemical admixtures on cement hydration

Many chemical admixtures are known to retard cement hydration. This is an intentional effect of retarders. However, for many other admixtures such as superplasticizers, it is mostly an undesired side effect that becomes more and more problematic in modern concrete with reduced clinker content. In this chapter, the general mechanisms that affect the hydration processes and the behavior of most chemical admixtures are described. This includes possible modification of the rates of the dissolution, nucleation, and/or growth of various phases as well as destabilization of the silicate–aluminate–sulfate balance. Because of the importance of polycarboxylate ether (PCE) superplasticizers and the flexibility in their molecular design, a special section presents information concerning their impact on hydration. Finally, sugars are discussed because they are the most used set retarders and that important steps have been made in studying their impact on retardation.