While dispersion mechanisms appear well understood in general terms, many details remain unresolved, in particular, cement-superplasticizer incompatibility.3 This term refers to specific combinations of cement and superplasticizers that show poor rheological properties unless excessive amounts of polymer are added, or for which the duration of the dispersion effect is extremely short.
These incompatibilities arise from the reactivity of cement and in particular from the calcium aluminate phases, which have the strongest initial reaction in the presence of water. The influence of the cement chemistry on superplasticizer performance is well established4, 16 and is attributed in part to the intercalation of the superplasticizers into hydration products.17 The intercalated polymer is lost for dispersion purposes and this decreases efficiency.18 In other cases, the efficiency of some polycarboxylates can be lowered because of competitive adsorption from sulfate ions.19