# Automated Control of the Fresh State of Industrial Concrete Behaviour by Rheometer Test Adjustment
## 7 Rheometer Test Adjustment  
### Adjustment Flow Chart  
To make the rheological control of the behaviour of concrete in a fresh state more widespread and replace traditional industrial tests, a campaign of tests is required to enable the adjustment of the testing profiles and the configuration of the device (blade, container, load cell).  
In this study, a procedure to adjust the rheological test that will be used in the automated control of the fresh behaviour of concrete was developed. In this case, two types of impellers were considered, named A and B, with substantially different geometries, and  
\begin{table}
\begin{tabular}{c c c c c} \hline \hline  & **Test Time (min)** & **10** & **15** & **20** & **30** \\ \hline \multirow{2}{*}{Developed (A)} & Yield value (Nm) & 0.79 & 0.66 & 0.40 & 0.38 \\  & Viscosity value (Nm min) & 0.33 & 0.36 & 0.40 & 0.44 \\ \hline \multirow{2}{*}{Contrast (C)} & Yield value (Nm) & 0.38 & 0.31 & 0.15 & 0.13 \\  & Viscosity value (Nm min) & 0.26 & 0.27 & 0.28 & 0.30 \\ \hline \hline \end{tabular}
\end{table}
Table 4: Rheological parameters in relative units.  
Figure 16: Yield value and viscosity value.  
Figure 17: Relationship between the viscosity and yield values.  
one rheological test (FCT), in which the pre-shear period and speed must be adjusted. The FCT was selected as the most suitable procedure for automated control because it provides information regarding the plastic viscosity and yield stress.  
Figure 18 presents the protocol suggested for adjusting the rheological procedure. The first step is to select one impeller (any impeller may be selected first) along with a high rotational speed and short pre-shear period. With this configuration, an FCT can be conducted (FCT0 in the flow chart) to verify that this speed provides a maximum torque near, but lower than, the maximum value permitted by the torque cell. If the torque is excessively low or high, the speed must be increased or decreased, respectively.  
Once the high initial speed is selected, the torque reduction in the FCT0 is analysed; if it is lower than 50%, a longer pre-shear period is suggested (limited to 90 s to avoid a test that is too long). In this case, another loop of the procedure starts with a new FCT to verify the new pre-shearing period (FCT1 in the flow chart). If the pre-shear period is longer than 90 s, the impeller should be changed, and the adjustment procedure should be started again with the new impeller (FCT0).  
When the torque reduction exceeds 50%, segregation must be visually checked. In the event of segregation, the following must be applied: reduced speed, repeated FCT1 to verify the torque reduction, and readjustment of the breakdown period if necessary. If segregation is not detected, the Bingham model can be used to define the flow curve of the concrete. Using this equation, the yield stress can be calculated to confirm that no  
Figure 18: Adjustment flow chart.  
negative values are obtained. If the yield stress is negative, the speed must be reduced, and FCT1 must be repeated again to verify the torque reduction and segregation (although segregation would not be expected at a lower speed).  
Once the yield stress is positive, the viscosity can be obtained, and the adjustment procedure is complete. As a result of the developed campaign, the impeller, rotational speed, and breakdown period for the flow curve test were adjusted. Using this protocol, concrete can be used with automated control.