## 4 Conclusions  
This study focused on the physical phenomena, such as fluidity, rheological properties, and compressive strength, of normal-strength, high-fluidity concrete (NSHFC) with a different type of polycarboxylate-based superplasticizer (NPCE):  
(1) When the amount of HPMC increased from 0.3% to 0.6%, the slump flow decreased due to the increase in the plastic viscosity of concrete. The elapsed ratio of concrete decreased due to the delay in the setting time of HPMC. Regardless of the amount and combinations of HPMC, ST had an effect on increasing fluidity and reducing the elapsed ratio, whereas WG had an effect on reducing fluidity and increasing the elapsed ratio. These results are similarly reflected in all combinations of VMAs.  
(2) Adding VMA caused a higher plastic viscosity compared to the plain sample. The plastic viscosity and yield stress showed a proportional relationship, regardless of the combinations of VMA and the elapsed time. Moreover, the plastic viscosity and yield stress decreased when the slump flow increased, and increased when the slump flow is decreased. This showed an inverse relationship between the plastic viscosity or yield stress and the slump flow.  
(3) The compressive strength at 28 days was found to be in the order of WG (36.1 MPa) > GG (29.7 MPa) > ST (25.9 MPa) > HL (24.8 MPa) > HH (24.4 MPa), compared to when VMA was used alone. When two or more types of VMA were added, the unique characteristics of VMA were exhibited and affected the compressive strength according to the combinations of VMA.  
(4) Using NPCE with VMA, it was possible to reduce the lack of fluidity and segregation, which were limited when using a polycarboxylate-based superplasticizer alone at low binders (350 kg/m\({}^{3}\)). In conclusion, the combination of three types of VMA showed the best fluidity (slump flow 595-630 mm at initial) without any segregation and bleeding, and the compressive strength at 28 days was also the highest at 34-37 MPa. From these results, the combination of PCE (2.0%) + HPMC (0.3%) + WG (0.1%) + ST (0.1%) showed an 18% higher plastic viscosity than Plain and a \(-\)4.4% lower yield stress than Plain. As a result, it was considered to have the best fluidity performance (slump flow 630 mm) of NSHFC.  
Data curation, T.-W.K.: Formal analysis, T.-W.K., H.-M.Y., H.-S.L. and C.-B.Y.: Funding acquisition, H.-S.L.: Investigation, H.-M.Y. and H.-S.L.; Methodology, T.-W.K., H.-M.Y., H.-S.L. and C.-B.Y.; Supervision, H.-M.Y. and H.-S.L.: Writing--original draft, T.-W.K., H.-M.Y., H.-S.L. and C.-B.Y.; Writing--review and editing, T.-W.K., H.-M.Y., H.-S.L. and C.-B.Y. All authors have read and agreed to the published version of the manuscript.  
This research received no external funding.  
Not applicable.  
The raw/processed data required to reproduce these findings cannot be shared at this time as the data also forms part of an ongoing study.  
This research was supported by R&D for businesses, suitable for small and medium-sized businesses and returning to Korea (S2304169), as well as the basic science research program through the National Research Foundation (NRF) of Korea funded by the Ministry of Science, ICT, and Future Planning (No. 2015 RIASA1037548).  
All authors declare that there are no conflict of interest.