## 3 Results and Discussion
### Physical-Chemical Characterization of the Waste Vitreous Enamels
#### 3.2.1 Determination of the Pozzolanic Activity of Waste Enamels  
In order to determine the feasibility of using of the waste vitreous enamels generated from the plant for four mounts (batches 1-4): as a type II admixture for the production of concrete in accordance with EN 206, first was tested their pozzolanic activities and determined activity indexes and the results are presented in Tables 6 and 7. An examination of the pozzolanic activity of the waste enamels WEP (batches 1 and 2) (Table 6) showed that it belongs to the class of 15 pozzolanic materials (the largest class), while by the values of its pozzolanic activity for batches 3 and 4 it belongs to class 5 of pozzolanic materials (lowest class). Waste enamel WETM, according to the values of pozzolanic activity also belongs to the class 5 of pozzolanic materials (Table 7). Additionally, both waste enamels meet the criteria for the activity index according to EN 450-1, which refers to their possible use as a type II admixture for the production of concrete in accordance with EN 206. Waste enamels WEP in terms of water requirement, initial setting time and soundness meet the criteria prescribed by the Standard. Waste enamels WETM, in terms of initial setting time and soundness met the criteria prescribed by the Standard, while the water \begin{table}
\begin{tabular}{c c c c c c} \hline \hline \multirow{2}{*}{**Property**} & \multicolumn{5}{c}{**Parameters/Results**} & \multirow{2}{*}{**Requirement**} \\ \cline{2-2} \cline{4-6}  & **Batch 1** & **Batch 2** & **Batch 3** & **Batch 4** & \\ \hline \multirow{4}{*}{Class of pozzolanic materials} & Flexural strength: & Flexural strength: & Flexural strength: & \(>\)2.0/4.0 mPa \\  & 4.5 mPa & 4.1 mPa & 2.1 mPa & 2.1 mPa & (class 5/15) \\  & Comp. strength: & Comp. strength: & Comp. strength: & Comp. strength: & \(>\)5.0/15.0 mPa \\  & 17.2 mPa & 16.8 mPa & 7.0 mPa & 7.4 mPa & (class 5/15) \\  & After 28 days: & After 28 days: & After 28 days: & After 28 days: & \\  & 80.80\% & 77.62\% & 75.24\% & 76.24\% & \(>\)75\% \\  & After 90 & After 90 & After 90 & After 90 & \(>\)85\% \\  & days—87.48\% & days—87.49\% & days—85.74\% & days—86.28\% & \\ Water requirement & 93\% & 94\% & 93\% & 94\% & \(<\)95\% \\ Standard & 29.5\% & 29.5\% & 30\% & 29.5\% & not prescribed \\  & 135 min & 145 min & 150 min & 140 min & \(<\)230 min \\ Final setting time & 160 min & 180 min & 180 min & 170 min & not prescribed \\  & Roundness & 1.0 mm & 1.0 mm & 1.0 mm & \(<\)10 mm \\ \hline \hline \end{tabular}
\end{table} 
Table 6: Pozzolanic activity and parameters of cement paste with the addition of WEP. \begin{table}
\begin{tabular}{c c c c c c} \hline \hline \multirow{2}{*}{**Property**} & \multicolumn{5}{c}{**Parameters/Results**} & \multirow{2}{*}{**Requirement**} \\ \cline{2-2} \cline{4-6}  & **Batch 1** & **Batch 2** & **Batch 3** & **Batch 4** & \\ \hline \multirow{4}{*}{Class of pozzolanic materials} & Flexural strength: & Flexural strength: & Flexural strength: & \(>\)2.0/4.0 mPa \\  & 2.8 mPa & 2.1 mPa & 2.1 mPa & 2.2 mPa & (class 5/15) \\  & Comp. strength: & Comp. strength: & Comp. strength: & \(>\)5.0/15.0 mPa \\  & 8.4 mPa & 7.0 mPa & 6.9 mPa & 7.2 mPa & (class 5/15) \\  & After 28 days: & After 28 days: & After 28 days: & \\ Activity index & 73.45\% & 78.62\% & 75.86\% & 76.78\% & \(>\)75\% \\  & After 90 & After 90 & After 90 & After 90 & \(>\)85\% \\  & days—85.10\% & days—89.29\% & days—86.13\% & days—87.08\% & \\ Water requirement & 98\% & 97\% & 100\% & 98\% & \(<\)95\% \\  & Standard & 31.0\% & 30.5\% & 31.5\% & 31.0\% & not prescribed \\  & consistence & & & & \\ Initial setting time & 175 min & 165 min & 185 min & 170 min & \(<\)230 min \\ Final setting time & 200 min & 190 min & 210 min & 200 min & not prescribed \\  & Soundness & 0.5 mm & 0.5 mm & 0.5 mm & \(<\)10 mm \\ \hline \hline \end{tabular}
\end{table} 
Table 7: Pozzolanic activity and parameters of cement paste with addition of WETM. requirement was slightly above the allowed value.