Calcium complexation and cluster formation as principal modes of action of polymers used as superplasticizer in cement systems

Superplasticizers are added to fresh concretes in order to improve workability. The interaction of superplasticizers with cement during hydration is not fully understood. It is investigated if the measured effects are principally related to the polymer structure and must therefore be considered in discussions.By means of titration experiments and utilizing a calcium selective electrode the quantification of complexed ions in aqueous solution is investigated. Adsorption of polymers both on cement and tricalcium silicate is analyzed by measuring the total organic carbon (TOC). Finally, the aqueous solution is investigated by analytical ultracentrifugation (AUC).Complexation of calcium ions by polymers is the result of attractive forces evoked by their functional groups. Thereby, complexation is observed both in solution and on surfaces (adsorption). Besides ion–polymer complexes it is demonstrated that also larger aggregates (clusters) of organic polymers and inorganic crystals are formed. Thus, superplasticizers exert three different principal modes of action.