# Influence of Mix Proportions on Rheological Properties, Air Content of Wet Shotcrete--A Case Study
## 4 Conclusions  
To investigate the influence of various admixtures on the fresh performance of shotcrete, the rheological properties and air content were measured. Through the comparative analysis of influencing factors and different analysis, it is helpful to understand the mix proportion design of fresh wet shotcrete. (1) When WC increases, the slump and air content increase generally, while the rheological parameters decrease. with the increase of SR, the slump decreases gradually, while the air content and the relative yield stress increase. The air content, rheological parameters showed an increasing trend, while slump decreases with the increase of fiber length. With the increase of air-entraining agent content, the air content and slump increase, while rheological parameters decrease. Rheological parameters and air content decrease with the increase of superplasticizer dosage while the slump is opposite. With the increase of fly ash, the slump value increases, and rheological parameters decrease. The addition of silica fume reduces the slump, and increases the rheological parameters. (2) With the increase of WC, the pressure drop decreases, i.e., smaller rheological parameters help to improve the pumping performance of fresh concrete. However, the high WC reduces the shootability. SR60 is the best value to obtain both good pumping performance and good shooting performance. Longer fibers help to reduce pressure drop and increase build-up thickness. The air-entraining agent can improve the pumpability \begin{table}
\begin{tabular}{c c c c c} \hline \hline \multirow{2}{*}{**Variable**} & \multicolumn{2}{c}{**Flowability Factor**} & \multicolumn{2}{c}{**Effect on Wet Shotcrete**} \\ \cline{2-5}  & **Ball Bearing Effect** & \begin{tabular}{c} **Free Paste Effect** \\ **or Filling Effect** \\ \end{tabular} & **Pumpability** & **Shootability** \\ \hline \multirow{3}{*}{Increasing WC} & Creating possibility for & & & \\  & entraining bubbles as & Producing more free paste & Positive at some certain & Negative for build-up \\  & ball bearing effect & & level & thickness; Positive for reducing rebound \\ \multirow{3}{*}{Increasing sand ratio} & Sand as ball bearing & Sand fills gaps to release & Positive & Negative for build-up \\  & effect & more paste & Positive & thickness; \\  & & & more paste & Positive for strength \\ \multirow{3}{*}{Fiber} & None & Adding fiber reduces free & \begin{tabular}{c} Positive due to \\ avoiding bleeding and \\ segregation \\ \end{tabular} & \begin{tabular}{c} Positive for build-up \\ thickness \\ \end{tabular} \\ \multirow{3}{*}{Air-entraining agent} & Bubbles as ball bearing & When bridge is broken, & Positive & \begin{tabular}{c} Positive when bubbles \\ were broken during \\ spraying \\ Negative \\ \end{tabular} \\ \multirow{3}{*}{Water reducer} & None & Releasing free cement paste & Positive & Negative \\  & & Dilution effect with lower & & \\ Fly ash & \begin{tabular}{c} Spherical geometry and \\ smooth surface as ball \\ bearing effect \\ \end{tabular} & \
\begin{tabular}{c} Specific gravity; filling \\ effect with small particle \\ size \\ \end{tabular} & Positive & Negative at some \\  & & & effect with small particle & & degree \\ \multirow{3}{*}{Silica fume} & Spherical geometry as &
\begin{tabular}{c} Filling effect with small \\ particle; flocculation \\ reducing paste \\ \end{tabular} & Positive for reducing & Positive for build-up \\  & & & bededing and & thickness \\ \hline \hline \end{tabular}
\end{table} 
Table 4: Summary of various factors affecting shotcrete in pumpability and shootability.