Applying the Bingham rheological model for the obtained flow curves of the modified Portland cement pastes (Figure 3), an exponential relationship was found between the different dosage of the plasticising admixtures and the paste yield stress [[tau].sub.0] (Figure 4a) as well as the plastic viscosity [[mu].sub.pl].
Increasing the dosage of the plasticising admixtures (LS, PCE or MAP) from 0 to 0.8% of cement weight, not only the flowability of modified Portland cement pastes increases (Figure 3), but also their rheological properties change (Figure 4).
It was found that the superplasticiser (PCE) reduces the yield stress and plastic viscosity of modified Portland cement paste more effectively than the plasticiser (LS) and the superplasticiser (MAP).
In the case of different plasticising admixtures (different chemical composition) and their dosages (from 0.2 to 1.2% of the cement weight), experimentally the change in water demand was determined for obtaining the modified Portland cement pastes of the equivalent viscosity (Figure 5).
Figure 5 shows that increasing the dosage of the plasticiser (LS) from 0.2 to 1.2% of the cement weight, the reduction in the water demand of the modified Portland cement paste is steadily increasing from 3 to 11%, while increasing the dosage of the superplasticiser (PCE and MAP) from 0.2 to 0.8%, the reduction in the paste water demand intensively increases from 15 to 30% and from 12 to 25%, respectively.