# Investigations of Mixing Technique on the Rheological Properties of Self-Compacting Concrete
## 3 Results and Discussion
### Effect of Mixing Speed on Rheological Properties of SCC  
Figure 8 shows the results of the effect of mixing speed on the slump-flow of SCC. A drastic drop in the slump-flow with increasing mixing speed is observed. This observation provides new insights into the concrete rheological properties, after appraising the previously published results. According to the literature [42; 43; 44], at low level mixing speed, the fluidity of common cement pastes was found to be increased with increasing the mixing speed. At high level mixing speed, as reported by [PERSON] and [PERSON] [45], among others, the fluidity of common cement pastes was decreased with an increase of the mixing speed.  
Obviously, at low level mixing speed, the fluidity of SCC is completely different from that of common cement pastes. This difference is attributable to the following aspects. First, the cementitious materials and SP suffer from the disturbance and shear force, exerted by the coarse aggregates. The actual mixing speed of the SCC can be approximately 2.5 times that of the equivalent paste mixing speed. Hence, the effect of mixing speed, at low levels, on the fluidity of SCC should be phenomenally judged as that, at high levels, on the fluidity of common cement pastes [30; 46]. Second, as continuous increase of the mixing speed, the SCC mixtures become increasingly condensed, and the fluidity correspondingly decreases. Third, mixing at a high speed can readily cause the SP molecules to intertwine, subsequently impairing their water-reducing effect and weakening the fluidity of the mixtures. Fourth, since the SP has a poor adsorption capacity [39; 47], it is reasonable to consider that with continuous increase of the mixing speed, the desorption phenomenon of the SP molecules becomes increasingly pronounced. As a result, the SP gradually loses its function as a water reducer and the fluidity of the SCC system turns to be weakened.  
Figure 9 displays the effect of mixing speed on the rheological parameters of SCC. As observed, the yield stress increases significantly with the increase of mixing speed. The plastic viscosity, however, exhibits a completely different trend, and it decreases in the opposite sense.  
Figure 8: Effect of mixing speed on the slump-flow of SCC.  
Figure 9: Effect of mixing speed on the rheological parameters of SCC.  
The rheological properties of SCC with different mixing speed, determined by curve-fitting of the modified Bingham model, are shown in Figure 10a. In the range of 15-45 r/min, the rheological curves all exhibit concave pattern, which proves the occurrence of the shear thickening behavior. Interestingly to note is that the rheological curves suddenly turn into convex pattern for mixing speed at 60 r/min, indicating the transition of shear thickening to shear thinning. Figure 10b shows the relationship between \(c/\mu\) and mixing speed. It is obvious that the \(c/\mu\) value decreases with the increase of mixing speed. This observation suggests that increasing the mixing speed can weaken the shear thickening behavior of SCC.  
The smaller the mixing speed, the more stable the sorbent. As the mixing speed is continuously increased, desorption of the SP molecules becomes more significant, and the shear thickening behavior of the SCC mixtures is concurrently weakened. Once the mixing speed is sufficiently high, the desorption phenomenon dominates the behavior of the SP molecules in mixing process. Under the disturbance of shear stress, re-adsorption of the SP molecules can take place, resulting in shear thinning behavior of the SCC mixtures [39].