# Recycling Red Ceramic Waste as a Raw Material for Lightweight Aggregates
## 3 Results and Discussion
### Characterisation of Lightweight Aggregates
#### 3.1.6 Crushing Strength (\(S\))  
The crushing strength results obtained are satisfactory from the point of view of engineering applications. According to Table 8, all the specimens produced exceeded the value of 2.3 MPa, a common reference for light aggregates commercially available in Brazil [30]. Among the highlights is sample R100, sintered at 1200 \({}^{\circ}\)C, which obtained the highest \(S\) value recorded among the samples that met the density criteria, exceeding 12.0 MPa.  
The formulations showed significant crushing resistance indices when sintered at 1100 and 1150 \({}^{\circ}\)C. On the other hand, there was a significant drop in \(S\) values as the temperature rose. There was a significant drop in \(S\) values as the temperature increased. In the R70 sample, for instance, crushing strength rose from 25.65 to 40.52 MPa but then  
\begin{table}
\begin{tabular}{c c c c c} \hline \hline \multirow{2}{*}{**Samples**} & \multicolumn{4}{c}{**Water Absorption (\(WA_{24H}\)) (\%)**} \\ \cline{2-5}  & **1100 \({}^{\circ}\)C** & **1150 \({}^{\circ}\)C** & **1200 \({}^{\circ}\)C** & **1250 \({}^{\circ}\)C** \\ \hline
**R100** & 6.7 & 0.7 & 0.6 & 1.7 \\
**R90** & 4.2 & 0.5 & 0.4 & 0.7 \\
**R80** & 3.4 & 0.3 & 0.6 & 0.5 \\
**R70** & 2.4 & 0.2 & 0.5 & 0.6 \\
**R60** & 1.6 & 0.1 & 0.4 & 0.5 \\
**R50** & 0.6 & 0.1 & 0.4 & 0.4 \\ \hline \hline \end{tabular}
\end{table}
Table 7: Water absorption (\(WA_{24H}\)) of the mixtures.  
\begin{table}
\begin{tabular}{c c c c c} \hline \hline \multirow{2}{*}{**Samples**} & \multicolumn{4}{c}{**Crushing Strength (\(S\)) (MPa)**} \\ \cline{2-5}  & **1100 \({}^{\circ}\)C** & **1150 \({}^{\circ}\)C** & **1200 \({}^{\circ}\)C** & **1250 \({}^{\circ}\)C** \\ \hline
**R100** & 10.29 & 29.07 & 12.01 & 2.64 \\
**R90** & 17.66 & 31.92 & 9.68 & 5.41 \\
**R80** & 19.42 & 31.77 & 8.81 & 7.30 \\
**R70** & 25.65 & 40.52 & 10.77 & 8.54 \\
**R60** & 32.78 & 36.76 & 9.76 & 9.68 \\
**R50** & 31.72 & 32.51 & 11.06 & 10.59 \\ \hline \hline \end{tabular}
\end{table}
Table 8: Crushing strength (\(S\)) of the mixtures.  
dropped to 10.77 and 8.54 MPa at 1200 and 1250 \({}^{\circ}\)C, respectively. These results show a strong correlation with the density and porosity data discussed above. Based on the reports by [PERSON] et al. [64], it is possible to assume that, at temperatures of at least 1200 \({}^{\circ}\)C, the high concentration of Fe\({}_{2}\)O\({}_{3}\), present in this cluster increased the degree of expandability of the samples, increasing their porosity and consequently reducing their resistance to crushing.  
As demonstrated in Table 8, in the majority of cases, there was a downward trend in resistance as the proportion of RCW increased. For example, at temperatures of 1250 \({}^{\circ}\)C, the \(S\) of the mixture formulated with 100 per cent RCW was approximately four times lower (2.64 MPa) than the value obtained for the sample made with 50 per cent RCW (10.59 MPa). As previously reported, the increase in RCW favoured the formation of a more porous structure. This consequently resulted in a reduction in the crushing resistance indices seen in the aforementioned temperature range. However, it should be emphasised that, regardless of the RCW content added or the temperature range adopted, all the specimens produced in this set had \(S\) values higher than those of an LWA commonly used in the production of structural concrete [30].