# Teaching Characteristics of Wood Biomass Fly Ash Cement Composites
## Materials and Methods
### Specimen Preparation and Testing Methods
Leaching testing per EN 12457-2:2005 [71] involved separating 20 g of WBA, placing it in a closed 250 mL bottle, and filling the bottle with 200 mL of solvent (deionised water) in order to attain a desired ratio of liquid/solid (L/S = 10). The glass bottle containing the sample-water mixture was rotated (mixed) for 24 h. After the mixing was complete, the mixture was allowed to settle for \(15\pm 5\) min. The eluate was then passed through a membrane filter with a pore diameter of 0.45 \(\upmu\)m. Analysis of the heavy metals concentration using a spectrometer with excitation in inductively coupled plasma--ICP-OES (ICPE 9000, Shimadzu) was preceded by sample stabilisation with 65% nitric acid. For determining the leaching characteristics of the monolithic cement paste samples, testing was performed per the CEN/TS 16637-2 standard (DSLT method) [73], wherein the release of substances to the environment is primarily controlled by diffusion. Construction products suitable for the DSLT include facades (brick, concrete, wood panels, glazing, and coatings), roof coverings, pavement samples (from concrete, stone, asphalt, and concrete slabs), foundations (concrete blocks and concrete), coastal protection, gravel railroad sections (track ballast), and glass tiles [74]. The DSLT involves periodic leaching solution replacement, as specified by the standard, to ensure a substantial difference in concentration between the solid and liquid phases. As compared to a leaching test for granular materials, the DSLT requires more time but provides information on the kinetic mobility of the harmful substances and complex leaching mechanisms [75]. For the monolithic sample leaching tests per CEN/TS 16637-2 [73], cement paste samples were prepared according to the EN 196-3:2016 [76] standard, see Table 4.  
After 3 days of ageing, leaching tests were performed on prism samples with dimensions of \(4\times 4\times 16\) cm. The leaching vessel was a closed polypropylene plastic container. The eluate sampling was performed at 0.25, 1, 2.25, 4, 9, 16, 36, and 64 days. Samples were submerged in demineralised and deionised water with a conductivity of less than 0.5 mS/m, such that the ratio of the volume of the liquid to the exposed mortar surface was L/S = 90 L/m\({}^{2}\), i.e., there was 90 L of solvent (deionised and demineralised water) to 1 m\({}^{2}\) of sample surface area. The solvent volume was obtained using the following expression:  
\[V_{l}\ =\ (L/A)\times AV_{1}\ =\ (L/A)\ \times\ A, \tag{1}\]  
where  
surface area of the tested sample in m\({}^{2}\), and  
_L/A_ must be equal to \(80\pm 10\) L/m\({}^{2}\). According to the standard, the distance between the solvent and the vessel bottom, i.e., the distance between the sample and the solvent surface, must be at least 20 mm. The solvent was removed from the vessel at specified times and replaced with the same amount of demineralised and deionised water until the end of the next period. The fluid removed was passed through a 0.45 \(\upmu\)m filter paper. \begin{table}
\begin{tabular}{c c c c} \hline \hline
**Sample Designation** & **Water, g** & **Cement, g** & **WBA, g** & **Standardized Consistency, \%** \\ \hline REF & 141.5 & 500 & - & 28.3 \\ M15-1 & 217 & 425 & 75 & 43.4 \\ M15-2 & 142 & 425 & 75 & 28.4 \\ M15-3 & 160 & 425 & 75 & 32.0 \\ \hline \hline \end{tabular}
\end{table} 
Table 4: Paste mix details. The pH and electrical conductivity of the removed fluid and the mass of the monolithic DSLT sample were measured. The filtered fluid was prepared for heavy metals concentration testing using ICP-OES (acidification with nitric acid to below pH 2 before testing). Leaching of the substance per unit of sample surface area is given by  
\[V_{I}\ =\ (L/A)\times Ar_{i}\ =\ (ci\ \times\ V/A)\ \times\ 0.01, \tag{2}\]  
where  
period i--period time from 1 to n,  
r\({}_{i}\)--leading value per unit surface area of the sample for the period i (i = 1 to 8), in mg/m\({}^{2}\),  
\(V\)--solvent volume in L, and  
\(A\)--surface area of the tested sample in m\({}^{2}\).