## 3 Results and Discussion
### Initial and Final Setting Time of Cement Paste  
A Vicat BC VIC-08 automatic instrument was used to determine the initial setting time and final setting time. The results of the test are presented by the values of the initial and final setting time of cement paste in Formulas R1 and R3. The results are presented in Table 4.  
The table presented above shows the results of the initial setting time and final setting time of the tests of Formulas R1 and R3. For Formula R1 with CEM I 52.5R, it has been demonstrated that a 25% replacement of pure mixing water with waste sludge water from the CP shortens the initial setting time by 23 min (11%) and shortens the final setting time by 16 min (6.7%). A 50% replacement shortens the initial setting time by 75 min (35.7%) and accelerates the final setting time by 78 min (32.5%). A 75% replacement shortens the initial setting time by 85 min (40.5%) and accelerates the final setting time by 78 min (32.5%). 100% replacement shortens the initial setting time by 100 min (47.6%) and accelerates the final setting time by 94 min (39.2%). For the R3 formula with CEM II/B-LL 32.5R, it  
\begin{table}
\begin{tabular}{c c c c c c c c c c c} \hline \hline  & & \multicolumn{3}{c}{**R1**} & \multicolumn{3}{c}{**R3**} \\ \hline  & **Com** & **25\%** & **50\%** & **75\%** & **100\%** & **Com** & **25\%** & **50\%** & **75\%** & **100\%** \\ \hline Initial setting time [min] & 210 & 187 & 135 & 125 & 110 & 200 & 170 & 145 & 132 & 120 \\ Final setting time [min] & 240 & 224 & 162 & 153 & 146 & 246 & 205 & 180 & 175 & 167 \\ \hline \hline \end{tabular}
\end{table}
Table 4: Values of the initial and final setting time of Formulas R1 and R3.  
Figure 3: Linear dependence of the diffusion value of Formulas R1 and R3 on the replacement of mixing water with waste sludge water from the concrete plant.  
\begin{table}
\begin{tabular}{c c c c c c c c c c} \hline \hline  & & \multicolumn{3}{c}{**R1**} & \multicolumn{3}{c}{**R3**} \\ \hline  & **Comp.** & **25\%** & **50\%** & **75\%** & **100\%** & **Comp.** & **25\%** & **50\%** & **75\%** & **100\%** \\ \hline Diffusion \(\mathcal{O}\) [mm] & 160 & 148 & 133 & 123 & 110 & 164 & 152 & 141 & 128 & 120 \\ \hline \hline \end{tabular}
\end{table}
Table 3: Consistency of fresh mixture.  
has been demonstrated that a 25% replacement of pure mixing water with waste sludge water from the CP shortens the initial of the setting time by 30 min (15%) and shortens the final setting time by 41 min (16.7%). A 50% replacement shortens the initial of the setting time by 55 min (27.5%) and accelerates the final setting time by 66 min (26.8%). A 75% replacement shortens the initial setting time by 68 min (34%) and accelerates the final setting time by 71 min (28.9%). 100% replacement shortens the initial setting time by 80 min (40.0%) and accelerates the final setting time by 79 min (32.1%). The facts stated above show that if the mixing water is replaced with more than 25% of waste sludge water from the CP, it is possible to extend the initial setting time of the cement paste by adding a suitable plasticizer or superplasticizer. However, a suitable type of plasticizing or superplasticizing additive must be verified by an experiment.  
Exponential functions are interleaved through the final values in the graphical expression of the initial and final setting time (see Figure 4). The suitability of using exponential function is based on the high value of the coefficient of determination that is close to 1. In case of Formula R1, the coefficient of determination R2 for the initial setting time is 0.95 and for the final setting time 0.89. In case of Formula R3, the determination coefficient R2 for the initial setting time is 0.98 and for the final setting time 0.89. These values show a very close dependence of the initial and final setting time on the replacement of pure mixing water with waste sludge water from the CP.