# Water Demand (or Specific Surface) of Aggregate as a Dominating Factor for SCC Composition Design
## 5 Discussion
The deviations from the parallel pattern and low fit (low R\({}^{2}\)) are most probably caused by the lower precision of the obtained results. In  
Figure 12: The assessment of \(\chi_{i}\) coefficient. \begin{table}
\begin{tabular}{c c c c c c} \hline \hline
**Shape of Grains/** & & & & & \\
**Aggregate Type** & \(\chi_{O}\) & \(\chi_{R}\) & \(\chi_{S}\) & \(\chi_{B}\) & \(t_{rel}\) (\(V_{p}\) = 350) \\ \hline Ideal spheres & 1.66 & 1.07 & 0.38 & 65.80 & 0.0561 \\ \hline Rounded grains & 1.55 & 1.00 & 0.355 & 61.45 & 0.0524 \\ (river origin) & 1.50 & 0.97 & 0.34 & 59.45 & 0.0507 \\ \hline Crushed coarse aggregate + river sand & 1.43 & 0.92 & 0.325 & 56.70 & 0.0484 \\ \hline Only crushed grains & 1.33 & 0.86 & 0.305 & 52.725 & 0.0449 \\ \hline \hline \end{tabular}
\end{table} 
Table 3: Comparison between \(\chi_{i}\) parameter values depending on the “base” \(\chi_{O}\) value and their influence on the final \(t_{rel}\) value. these cases the research program was not designed to minimize the error in the same way like in the case of the results shown in Figures 10 and 11. Moreover, the range of values taken into account as one series in the case of Figures 13-15 is wider. This resulted in some cases in more than one data point covered by a given consistency range, see example in Figure 14. Each such case significantly increases the standard deviation value and reduces the resulting R\({}^{2}\) value. This may significantly affect the final angle of inclination of the obtained regression line. In summary, the presented method allows determination of the paste demand line for any SCC consistency test in scope (slump flow and viscosity measures) at any selected limit value. It should be noted that in the described method, it is not possible to estimate the content of cement paste necessary to increase consistency using an integrated consistency factor (like in the case of traditional water demand assessment methods). Here, this is performed by parallel shifting of the paste demand line along the line of increasing paste content, as shown in Figures 13 and 14; the line is shifted along both axes, not along the \(t_{\text{rel}}\) axis solo. The SCC composition design method using proposed minimum paste demand line may be summarized as follows [19]. 1. Design 4 mixes of extreme compositions in terms of \(t_{\text{rel}}\) using the method proposed in Sections 2.5.2 and 2.5.3. This means that 2 extreme values of both _w/b_ ratios (for extreme \(\sum_{p}\) obtaining) and water demand/specific surface of aggregate (for extreme \(\sum_{a}\) obtaining) are to be selected. As a quick indicator of the second value, a sand (i.e., aggregate up to 2 mm)-to-total aggregate ratio (_s/a_) may be used. 2. Test the designed mixes according to Section 2.5.4. The target is to obtain the assumed consistency level. 3. Calculate \(t_{\text{rel}}\) values for the designed concrete compositions and plot linear regression curve in the \(V_{p}-t_{\text{rel}}\) space to obtain the minimum paste demand line. 4. Design composition conforming to a pre-assumed specification (e.g., strength class, etc.) of \(t_{\text{rel}}\) within the range covered by the line and read predicted \(V_{p}\) for this case. 5. Prepare the trial batch using predicted \(V_{p}\) and adjust (rise) _sp_ if necessary. Figure 13: The influence of slump flow diameter D\({}_{0}\) on the ONT model (15), assuming \(\chi_{0}=1\). Figure 14: The influence of t\({}_{500}\) time on the ONT model (15), assuming x\({}_{\rm O}\) = 1. Figure 15: The influence of V-funnel t\({}_{\rm V}\) time on the ONT model (15), assuming x\({}_{\rm O}\) = 1. In the present version, the proposed approach enables to predict paste volume for SCC assuming a given aggregate and paste compositions. Unfortunately, it underestimates the superplasticizer dose (_sp_). The procedure of cement paste assessment described in Section 2.5.3 sets a bottom limit for _sp_, not a target value. Obtaining a more reliable _sp_ will be the next step of the presented approach development.