A review of cement–superplasticizer interactions and their models

This paper presents a focused review of cement–superplasticizer interactions. It has been concluded from the survey of the literature that cement–superplasticizer interactions are generally preceded by the adsorption of superplasticizers on the hydrating cement particles. However, the mechanisms of such adsorptive interactions have not been adequately addressed experimentally or discussed in the literature. The reason for this appears to be the lack of a conceptual model that can delineate the results to date and project needed experiments. A charge-controlled-reaction mechanism model involving Ca²⁺ ions from initial hydration is proposed to explain the adsorption characteristics of superplasticizers and other organic additives and their effects. The calcium ions released by hydration form a bilayer immediately upon contact of water with the cement, which is followed by adsorption of superplasticizer anions on the Ca²⁺ ion side of the bilayer. The interfacial structures and their influence on electrical characteristics, hydration reactions and phase growth in the hydrating cement are discussed in terms of the proposed model.