## 3 Results and Discussion
### Thermal Gravimetric Analysis  
The TGA test was selected as a calibration indicator of the mechanical behavior of the sustainable bricks because it permits the determination of the limit (or fire resistance) and link to the matrix basic components. The TGA results presented in Figure 7 indicate a weight loss, for all samples studied, ranging from 14% to 18% with respect to the initial weight. The maximum loss band is located in the adjacent  
Figure 6: Compressive strength and initial maximum absorption values. range between 300 \({}^{\circ}\)C and 600 \({}^{\circ}\)C; limits were established by the moving average curves with base 30 (\(\overline{X}_{30}\)) (Equation (1)) (30 was the value selected to determine the curves for favoring a better sensitivity coupling to the curves obtained from the TGA):  
\[\overline{X}_{30}=\frac{\sum_{i=1}^{n}x_{i}}{n} \tag{1}\]  
where: (\(\overline{X}_{30}\)) = moving average; \(n=30\), where each individual value (\(x_{i}\)) represents the percentage difference of weight loss between consecutive TGA measurements. The weight loss (from the limits of the bands previously established) to the final weight ratio was obtained by comparing the partial and total areas under the curves: percentage weight loss vs. temperature increase. The calculation process was based on the trapezoid method according to Equation (2) for each pair of increase values of its weight loss percentage (\(W\)) and its respective temperature (\(T\)), in order to determine the total area under the desired curve. \[\int_{0}^{i}f(x)dx=(t_{2}-t_{1})\bigg{[}\frac{W_{1}+W_{2}}{2}\bigg{]} \tag{2}\]  
where: \(t_{1}\  
V-AiO-M (11% weight loss compared to the initial weight, representing a 1% reduction) (Figure 8b). In both cases, the correlation between mechanical resistance increase or absorption reduction and weight loss reduction indicates microstructural improvements (better union of constituent particles) and increased densification of the sustainable brick matrix. As regards the use of OC and AiO materials, the comparison between the two curves shows a 1% difference between them, indicating that the use of AiO material in the matrix is clearly appropriate. In order to determine the compounds or materials that contribute to the mechanical improvement of the matrix of the different samples, Figure 9 presents the compounds and materials identified in previous studies. Absorbed water, organic charcoal, wood residues, clay minerals, pyrite, kaolinite, illite and alpha quartz have a significant impact on weight loss (shaded area). The general behavior of each one of the study samples may possibly be due to the total combination of the different compounds constituting it. However, it is also evident that some of these compounds may have a significant direct impact. Thus, in order to determine the incidence of each one of the compounds or materials, a comparison of the areas below the curves in the maximum loss range was performed for each compound present in this zone. Figure 8: (**a**) Thermal Gravimetric Analysis (TGA) of OC; (**b**) TGA of AiO. Figure 9: Weight loss ranges for different materials due to the increase in the temperature of ceramic matrices. Data from [20; 21; 23; 26; 39; 40]. The comparison between V-OC-M and its reference highlighted three compounds that showed a higher incidence, which are, in descending order of importance in the matrix: wood residues, clay minerals and illite. Similarly, the comparison between V-AiO-M and its reference established that wood residues and clay minerals were also the two compounds having the greatest impact on the general behavior of the samples, the third one being, in this case, organic carbon [40]. Illite (to a greater extent) and kaolinite (to a lesser extent) are present in both mixtures (V-OC-M and V-AiO-M), both compounds being more abundant in the first mixture, and thus causing the greatest weight loss by incineration.