# Influence of Mix Proportions on Rheological Properties, Air Content of Wet Shotcrete--A Case Study
## 3 Results and Discussion
### Influence of Various Factors on Rheology and Air Content of Fresh Wet Shotcrete  
#### 3.1.1 Effect of Water to Binder Ratio (WC)  
Figure 3 describes the effect of WC on the properties of fresh wet shotcrete. When WC increases from 0.45 to 0.60, the slump and air content increase, while the rheological parameters (relative yield stress and viscosity) decrease. It can be explained that the larger the WC, the more the free water content in the fresh wet shotcrete, the thicker the outer paste coating of the particles, the larger the spacing between particles, and the bigger the fluidity. In addition, fresh concrete with higher fluidity creates more opportunities for the introduction of air bubbles into the concrete mixture [49]. On the contrary, these bubbles act as \"ball effect\" to improve the fluidity of fresh wet shotcrete. This schematic diagram is shown in Figure 4. These trends are similar to [PERSON]'s report [35], where they measured rheological properties using an IBB rheometer with an H-shaped impeller. The internal structure of the two rheometers is different, such as the shape of the rotor, rotation speed, the size of the rheometer and the distance between the inner and outer rotors. Hence, the relative rheological values measured in the two studies are different. However, the rheological parameters obtained in this study also provide meaningful practical knowledge for guiding the mix proportion of wet shotcrete. It can be seen from Table 3 that with the increase of WC, the pressure drop decreases, i.e., smaller rheological parameters (yield stress and plastic viscosity) help to improve the pumping performance of fresh concrete. However, the high WC reduces the build-up thickness of concrete, and the shootability of fresh concrete with good pumping performance is poor. The author [35] also pointed out that high WC might be beneficial to pumping performance, but low viscosity and low yield stress might reduce the thickness of the build-up layer. From another point of view, [PERSON] et al. [50] pointed out that based on the assumption of better aggregate embedding, the viscosity and yield stress of shotcrete need to be lower to minimize the rebound rate. As shown in Figure 5, the wet shotcrete with low fluidity has a strong cohesive force, which increases the accumulation thickness \(h_{1}\). At the same time, we redefine \(F_{1}\) as the force that prevents particles from entering the shotcrete matrix, because the \(F_{1}\) is greater than the incident force \(F_{2}\), it may cause certain rebound. On the contrary, wet shotcrete with high fluidity provides convenience for aggregate embedding and reduces rebound. However, it is easy to collapse, resulting in a very thin accumulation of \(h_{2}\). \begin{table}
\begin{tabular}{c c c c c c} \hline \hline \multirow{2}{*}{**No.**} & \multirow{2}{*}{\begin{tabular}{c} **Pressure Drop** \\ **(MPa/m)** \\ \end{tabular} } & \begin{tabular}{c} **Build-Up** \\ **Thickness** \\ **(mm)** \\ \end{tabular} & **No.** & \
\begin{tabular}{c} **Pressure Drop** \\ **(MPa/m)** \\ \end{tabular} &
\begin{tabular}{c} **Build-up** \\ **Thickness** \\ **(mm)** \\ \end{tabular} \\ \hline WC45 & 0.09 & 170 \(\pm\) 20 & AE0.06\% & 0.03 & 130 \(\pm\) 20 \\ WC50 & 0.08 & 160 \(\pm\) 20 & WR0.3\% & 0.04 & 160 \(\pm\) 20 \\ WC55 & 0.04 & 140 \(\pm\) 20 & WR0.6\% & 0.04 & 150 \(\pm\) 20 \\ WC60 & 0.03 & 130 \(\pm\) 20 & WR0.9\% & 0.03 & 150 \(\pm\) 20 \\ SR50 & 0.07 & 170 \(\pm\) 20 & WR1.2\% & 0.03 & 130 \(\pm\) 20 \\ SR60 & 0.05 & 180 \(\pm\) 20 & SF5\% & 0.07 & 170 \(\pm\) 20 \\ SR70 & 0.09 & 160 \(\pm\) 20 & SF10\% & 0.08 & 170 \(\pm\) 20 \\ FI6 & 0.08 & 190 \(\pm\) 20 & SF15\% & 0.10 & 190 \(\pm\) 20 \\ FI12 & 0.07 & 190 \(\pm\) 20 & FA5\% & 0.05 & 180 \(\pm\) 20 \\ FI29 & 0.06 & 190 \(\pm\) 20 & FA10\% & 0.04 & 170 \(\pm\) 20 \\ AE0.02\% & 0.05 & 150 \(\pm\) 20 & FA15\% & 0.03 & 160 \(\pm\) 20 \\ AE0.04\% & 0.04 & 130 \(\pm\) 20 & & & \\ \hline \hline \end{tabular}
\end{table} 
Table 3: Results of pumpability and shootability tests of fresh concrete.