Adsorption of chemical admixtures

Abstract The properties of most of admixtures come from their ability to adsorb on the surface of particles (as observed for water reducers, superplasticizers, and retarders) or on the liquid–vapor interface (e.g., for air-entraining or shrinkage-reducing admixtures). Their adsorption behavior depends not only on their chemical composition, molecular structure, and dosage but also on the characteristics of the adsorbent surface and the composition of the liquid phase. This is particularly important during cement hydration, when the formation of new phases and an evolving ionic activity may alter strongly adsorption efficiency of admixtures. In practice, the determination of an adsorption isotherm allows for comparing the adsorption behavior of admixtures. The most common way to quantify the amount of adsorbed molecules is the solution depletion method. This method and its limitations, as well as the modeling of the adsorption isotherm, are deeply discussed to show that adsorption measurements and their interpretation are not trivial.