# Teaching Characteristics of Wood Biomass Fly Ash Cement Composites
## 3 Results and Discussion
### Leading from the WBA and Crushed Cement Composites with 15% WBA as Cement Replacement  
When landfilling any waste, the appropriate procedures and criteria should be followed. In consideration that most WBA is currently disposed of as waste (70% in Europe and 61% in Croatia), the WBA leaching values were compared to the leaching value limits for the waste categories (inert, non-hazardous, and hazardous waste) prescribed in the \"EU Directive 1999/31/EC\" [78; 79] and shown in Table 6.  
Results of the heavy metals concentration testing of the WBA eluate samples (F1, F2, and F3) are given in Table 6 along with the results of the heavy metals concentration testing of the crushed mortar samples with 15% WBA used as a cement replacement (M0, M1, M2, and M3). These samples represent the end-stage of the construction material life cycle, disposal. From Table 6, Zn and Cr had the highest concentrations of the WBA eluates (F1, F2, and F3). Significant Cr leaching was observed for all WBAs tested, especially for sample F1. By comparing the results for the heavy metals Pb, Ni, Zn, Cr, Cd, and Cu in the WBA eluates (F1, F2, and F3) with the values obtained for the crushed mortar samples (M1, M2, M3), when the WBA was incorporated into the cement mortar, significant decreases in the heavy metals concentrations were observed. This can be explained by the reduced heavy metals mobility, i.e., the incorporation of the heavy metals into the cement matrix [80], and confirms that the heavy metals were successfully encapsulated within the cement matrix. Based on the values obtained, assessments of the bonding of the heavy metals in the new environment (cement matrix) and environmental safety can be performed. The leaching ratio is a useful index for safety assessment: larger values for metal solidification, i.e., lower concentrations of leached metal, indicate a lower environmental impact and greater safety when using and disposing of the material. Figure 1 shows that the Cr leaching values were significantly high in the WBA eluates, but when the WBA was used in the cement composites, these values decreased substantially. The same trend was observed for the other metals (Cd, Cu, Pb, and Zn) except Ni, the concentration of which was 27.42% greater in the M2 sample than in the reference mixture. Large values for Cr leaching from the WBAs themselves were observed in [57], but the authors concluded, through the testing of crushed mortar, that the metals chemically bond in the mineral phase or are absorbed by the cement matrix, and the same was observed when coal ash was used in concrete. However, the testing of WBA eluates in [81] did not reveal Cr leaching or deviations from limit values. \begin{table}
\begin{tabular}{c c c c c c c c c c c} \hline \hline  & \multicolumn{3}{c}{**Eluate of Samples WBA1,**} & \multicolumn{3}{c}{**Crushed Mortar with 15\% WBAs 1, 2 and 3,**} & \multicolumn{3}{c}{**Leading Limit Values Based on WAC**} \\  & \multicolumn{3}{c}{**WBA2 and WBA3, mg/kg**} & \multicolumn{3}{c}{**and the Reference Mixture, mg/kg**} & \multicolumn{3}{c}{**(Waste Acceptance Criteria), mg/kg, L/S = 10**} \\ \hline  & **F1** & **F2** & **F3** & **M0** & **M1** & **M2** & **M3** & **Inert Waste** & **Non-Hazardous** & **Hazardous** \\  & & & & & & & & & & **Waste** & **Waste** \\ \hline C4 & 0.02 & 0.107 & \textless{}0.01 & 0.056 & 0.02 & 0.061 & 0.108 & 0.04 & 1 & 5 \\ Cr & 8.35 & 6.681 & 4.10 & 1.241 & 0.07 & 1.081 & 0.778 & 0.5 & 10 & 70 \\ Cu & 0.48 & 0.12 & 0.034 & 0.23 & 0.18 & 0.33 & 0.31 & 2 & 50 & 100 \\ Ni & 0.04 & 0.047 & 0.051 & 0.024 & 0.04 & 1.449 & \textless{}0.006 & 0.4 & 10 & 40 \\ Pb & \textless{}0.05 & 3.41 & 0.010 & \textless{}0.05 & \textless{}0.05 & \textless{}0.05 & 0.224 & 0.5 & 10 & 50 \\ Zn & 0.63 & 15.722 & 0.086 & 1.172 & 0.02 & 0.652 & 1.137 & 4 & 50 & 200 \\ \hline \hline \end{tabular}
\end{table} 
Table 6: Heavy metal concentrations and limited values for the individual waste categories [78,79].