Superplasticizers cement paste viscosity

Superplasticizers reduce both the yield value and plastic viscosity [24] of cement pastes. At higher dosages (for example 0.8% for SNF) [5, 6], the yield value approaches zero and the system becomes essentially Newtonian. 

The cement composition affects the rheological behavior of the system cement pastes having low C3S/ C2S and C3A/C4AF ratios have a higher viscosity when the superplasticizer addition is delayed [27],... 

Figure 10 shows the effect of a SMF-based superplasticizer on a cement paste. Large irregular agglomerates of cement particles predominate in a water suspension (Fig. 10a). The addition of a superplasticizer causes dispersion into small particles (Fig. 10b). A viscometer is used to measure the effect of a superplasticizer on rheology. Figure 11 plots the viscosity changes in cement containing SNF exposed to different times.

At any particular time, the viscosity is lower for the paste containing the admixtures. It has been reported that 1% superplasticizer at a w/c ratio of 0.3 shows the same fluidity as cement paste at a w/c ratio of 0.4 without the admixture. 

Superplasticizers are a class of materials which reduce viscosity and yield stress of the cementitious mixture. Superplasticizers have their sulfonic groups oriented towards water with their other side attached to cement grains. They form a monolayer arormd the grains. The water trapped within the original flocks is released and contributes to the mobihty of the concrete paste and its workabihty (reduced viscosity within a certain time frame). Superplasticizers do not have much effect on sirrface tension of water. ... 

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