## 3 Results
### LWA Characterization  
#### 3.2.1 Physical and Chemical Properties  
Table 5 summarizes the properties of the LWAs obtained; the data were compared to the reference sample containing only clay.  
The percentage of weight loss is an index that helps to understand how much water, organic material and other volatiles are lost from the aggregates subjected to the various thermal cycles mentioned above. After firing, the weight loss was slightly greater in Char 7.5% (due to the presence of coffee in this sample (23%)) compared to the sample containing only char (20%), so we can assume that the added char and coffee waste behaved in similar ways.  
Water absorption after 24 h was around 25%, with no significant differences between the two kinds of samples.  
As regards density, it is possible to note from the results that the LWAs obtained had an apparent density \(<\) 1200 kg/m\({}^{3}\), which is characteristic of light aggregates, a positive parameter that resulted in their lightness and high porosity. The Char 0% sample without a pore-forming agent did not fulfil the requirements. Furthermore, it can be seen that the LWAs containing only char (Char 15%) were slightly lighter than those with char and coffee (Char 7.5%). The true density depends on the composition of the aggregates, and it can be seen that there were no significant differences between the two prepared compositions, which are very close to the true density of the sample containing only clay. Further, the total porosity was calculated using the bulk and true densities with Equation (3). The aggregates (both Char 7.5% and Char 15%) had porosity percentages around 65%, compared to 50% for Char 0%, due to the fact that, during firing, the unburned organic matter present in the pyrolysed char and present in the SCG burned with the development of gas, which allowed the formation of pores. From these results, it can be seen once again how the char used behaved similarly to coffee waste, a positive factor in its reuse since it is suitable both  
Figure 3: Specific energy used to pyrolyse cork waste samples under different conditions.  
\begin{table}
\begin{tabular}{l l l l} \hline \hline
**Property** & **Char 0\% (Only Clay)** & **Char 7.5\%** & **Char 15\%** \\ \hline
**Water absorption (\%)** & 7.27 & 24.14 & 26.26 \\
**Weight loss (\%)** & 16.50 & 23.40 & 20.40 \\
**Shrinkage after firing (\%)** & 7.50 & 7.19 & 6.75 \\
**True density (kg/m\({}^{3}\))** & 2690 \(\pm\) 1.1 & 2725 \(\pm\) 1 & 2715 \(\pm\)0.4 \\
**Apparent density (kg/m\({}^{3}\))** & 1330 \(\pm\) 2.0 & 951.7 \(\pm\) 2.4 & 924.0 \(\pm\) 1.7 \\
**Porosity (\%)** & 50.55 & 66.10 & 64.94 \\
**pH** & 7.16 & 7.22 & 7.41 \\
**Electrical conductivity** & 1.15 & 0.345 & 0.311 \\ (mS/cm) & & & \\ \hline \hline \end{tabular}
\end{table}
Table 5: LWA characterization results.  
as a pore-forming agent and as a weight and density reducer. Figure 4 shows the LWAs obtained using the high percentage of Char (15%).  
Two tests were carried out for both pH and electric conductivity in order to improve reproducibility. The data obtained showed how the pH settled at neutral values for the LWAs created, which are optimal for subsequent use in the agronomic field. As regards the specific conductivity of the aggregates (measured in mS/cm), in general, 2 mS/cm represents the limit at which the soil is suitable for any type of crop and, consequently, is not subject to any risk [30; 31].  
In this case, all the results obtained fell well below this limit, which allows us to think about the use of these aggregates in any type of soil.  
It should be noted that, on average, the Char 15%, while presenting a greater amount of char, resulted in LWAs with a lower electrical conductivity.  
Given its neutrality and its low electrical conductivity, Char 15% was selected as the best sample for agronomic use, as it allowed reuse of an amount of pyrolysis waste double that of Char 7.5%.