## 3 Results
### Characterization of Biomass Bottom Ash
\begin{table}
\begin{tabular}{c c c} \hline \hline
**Compound** & **BBA, Wt. \%** & **BBA [60], Wt. \%** \\ \hline K\({}_{2}\)O & \(45.2\pm 0.25\) & \(16.47\pm 0.19\) \\ CaO & \(8.98\pm 0.14\) & \(25.29\pm 0.22\) \\ SiO\({}_{2}\) & \(8.96\pm 0.14\) & \(26.21\pm 0.22\) \\ SO\({}_{3}\) & \(6.43\pm 0.12\) & \(0.420\pm 0.021\) \\ Cl & \(4.72\pm 0.11\) & \(0.1750\pm 0.0087\) \\ MgO & \(4.04\pm 0.1\) & \(7.58\pm 0.13\) \\ P\({}_{2}\)O\({}_{5}\) & \(3.56\pm 0.09\) & \(6.03\pm 0.12\) \\ Al\({}_{2}\)O\({}_{3}\) & \(1.64\pm 0.06\) & \(4.54\pm 0.10\) \\ Fe\({}_{2}\)O\({}_{3}\) & \(0.864\pm 0.043\) & \(1.97\pm 0.07\) \\ Na\({}_{2}\)O & \(0.623\pm 0.031\) & \(0.274\pm 0.024\) \\ ZnO & \(0.197\pm 0.0098\) & \(0.0099\pm 0.0021\) \\ TiO\({}_{2}\) & \(0.0728\pm 0.0036\) & \(0.240\pm 0.012\) \\ SrO & \(0.0533\pm 0.0027\) & \(0.1340\pm 0.0067\) \\ MnO & \(0.0312\pm 0.002\) & \(0.1010\pm 0.0050\) \\ Rb\({}_{2}\)O & \(0.0237\pm 0.0037\) & - \\ NiO & \(0.0221\pm 0.0016\) & 0.0277 \(\pm\) 0.0015 \\ CuO & \(0.0207\pm 0.0021\) & - \\ Cr\({}_{2}\)O\({}_{3}\) & \(0.0105\pm 0.002\) & \(0.0137\pm 0.0018\) \\ \hline \hline \end{tabular}
\end{table} 
Table 5: X-ray fluorescence results of biomass bottom ash from this research and biomass bottom ash from the combustion of olive-pruning remains and vegetable-fat wastes [60]. problems. The results of the leachate test, carried out according to the standard mentioned in the methodology, are shown in Table 6.  
The leachate test shows that the concentration of the pollutant elements set is below the limits established by the Spanish-European regulations for waste [61]. It should be noted that the chlorine and sulfur elements detected in the X-ray fluorescence and X-ray diffraction tests have resulted in reduced leaching of chlorides and sulfates. Heavy metals are found in low concentration, mainly because these elements are difficult to find in the biomass used. Once the physical properties of the biomass bottom ashes were analyzed, the physical properties of the ashes were determined. The first of the tests carried out was the determination of the grading curve by means of the laser particle size test. The grading curve of the biomass bottom ash, after treatment, is shown in Figure 3.  
The grading curve of biomass bottom ash represents a continuous grading. Particles smaller than 0.063 mm represent a percentage higher than the 70% established by European regulations, and there are no particles larger than 2 mm. Therefore, and based on the \begin{table}
\begin{tabular}{c c c} \hline \hline
**Element** & **BBA, \(\mu\)g/kg** & **Maximum Limits, \(\mu\)g/kg** \\ \hline Ba & \(182\pm 5\) & 17,000 \\ Cd & \(2\pm 1\) & 9 \\ Cr & \(2\pm 1\) & 500 \\ Mo & \(1\pm 1\) & 500 \\ Ni & \(9\pm 1\) & 400 \\ Pb & \(1\pm 1\) & 500 \\ Se & \(2\pm 1\) & 100 \\ V & \(3\pm 1\) & 1300 \\ Zn & \(12\pm 1\) & 1200 \\ As & \(2\pm 1\) & 500 \\ Cu & \(9\pm 1\) & 2000 \\ Hg & - & 10 \\ Sb & \(1\pm 1\) & 60 \\ Chloride & \(134\),\(000\pm 3000\) & 800,000 \\ Sulfates & 86,000 \(\pm\) 3000 & 377,000 \\ \hline \hline \end{tabular}
\end{table} 
Table 6: Concentration of chemical elements in biomass bottom ash leachate compared to regulatory limits, UNE-EN 12457-3 standard. Figure 3: Biomass bottom ash grading curve. grading curve analyzed for the biomass bottom ash, it can be stated that the grading curve of the ashes after treatment is suitable for use as a filler in bituminous mixtures. Subsequently, in order to characterize the surface of the biomass bottom ashes at high magnifications and to provide valuable qualitative information, the ashes were analyzed by scanning electron microscopy. The images obtained from the scanning electron microscope are shown in Figure 4.  
Scanning electron microscope images of biomass bottom ash reflect a very irregular ash surface. Micropores and cavities abound on the surface of the ashes, which have a significant influence on the higher specific surface area. The existence of a higher specific surface conditions a higher bitumen absorption in bituminous mixtures.