## 3. Results and Discussion
### Rheological Performance  
Figures 3 and 4 show the consistency curve of the fresh concrete added with NPCE prepared by VMA combinations at an initial time and after 60 min, respectively. The plastic viscosity and yield stress are derived by applying the Bingham model to these results. Moreover, the plastic viscosity and yield stress of the fresh concrete are depicted in Figures 5 and 6, respectively. With the addition of only PCE (plain), the plastic viscosity is found to be at 1.11 Pa s at the start time and 1.21 Pa s after 60 min of testing. Moreover, the yield stress is found to be at 2.89 Pa at an initial time and 3.45 Pa after 60 min of testing. With the addition of PCE with one type of VMA (HL, HH, WG, GG, and ST), the plastic viscosity of WG samples is the highest, followed by GG, HH, HL, and ST. Moreover, the yield stress of WG samples is also the highest compared to other types of VMAs. It shows that WG is strongly adsorbed onto cement particles, and this adsorption could be the reason for the increase in the yield stress due to bridging flocculation. In particular, when ST is added, the plastic viscosity value is found to be similar to the plain sample, but the yield stress is reduced. Due to this, slump flow is improved, but shows a more severe segregation.  
With the addition of PCE with two types of VMA (HLW and HHW), plastic viscosity and yield stress of the HHW sample are higher compared to the HLW sample. It is considered that the viscosity of concrete increased as the amount of HPMC increased from 0.3% to 0.6%.  
With the addition of PCE with three types of VMA (HLWG, HLWS, HHWG, and HHWS), the plastic viscosity and yield stress of HHWG are the highest, followed by  
\begin{table}
\begin{tabular}{|c|c|c|c|c|c|} \hline  & **Plain** & **HL** & **HH** & **WG** & **GG** & **ST** \\ \hline Initial & & & & & \\ \cline{2-6}  & 565 mm \(\times\) 545 & 660 mm \(\times\) 6  
the HLWS, HHWG and HHWS sample. It is considered that the combinations of GG increased the plastic viscosity of concrete more than with the combinations of ST, because the cohesion of GG is stronger than that of ST in cement paste. In summary, adding VMA shows a higher plastic viscosity when compared to plain samples [39; 40; 41; 42]. The plastic viscosity and yield stress show a proportional relationship regardless of the combinations of VMA and the elapsed time. Moreover, the plastic viscosity and yield stress decrease when the slump flow is increased and vice versa. An inverse relationship is found between the plastic viscosity or yield stress and the slump flow [43].  
Figure 3: Consistency curves of fresh concrete added with NPCE prepared by VMA combinations at the initial time. (**a**) Combinations of one type of VMA only. (**b**) Combinations of two types of VMAs. (**c**) Combinations of three types of VMAs.  
Figure 4: Consistency curves of fresh concrete added with NPCE, prepared by VMA combinations after 60 min. (**a**) Combinations of one type of VMA only. (**b**) Combinations of two types of VMAs. (**c**) Combinations of three types of VMAs.  
Figure 5: Plastic viscosity and elapsed ratio of fresh concrete by different combinations of VMAs.