Jeknavorian – Impact of Water Reducers and Superplasticizers on the Hydration of Portland Cement
Ara A. Jeknavorian, Ph.D.
Research Fellow, W.R. Grace – Conn., Cambridge, MA
In conjunction with their cement dispersing function, normal and high range (superplasticizing) chemical admixtures almost invariably affect the rate of the cement hydration process. For a given cement, this affect can vary significantly depending on the chemistry of the cement dispersing agent, the addition rate, the time of addition relative to the initiation of cement hydration, and the amount of dispersant adsorbed on the cement surface as a function of time. Further complicating our understanding of the impact of these additives on cement hydration are the selective interactions between the type of additive and the major and minor compounds and phases of the cement, and the various associated mechanisms that can delay the rate of cement hydration. Such mechanisms can include nucleation poisoning, alterations to the semipermeable barrier formed during the induction period, and calcium chelation. In this paper, the major classes of normal and high range water reducing chemistries are ranked as to their impact on cement hydration, especially as related to their cement dispersing power, and the various mechanisms associated with changes in cement hydration are reviewed.