# Recycling Red Ceramic Waste as a Raw Material for Lightweight Aggregates
## 2 Materials and Methods
### Methods
#### 2.2.4 Sample Classification  
The parameters of particle density (\(\rho d\)), compressive strength (\(S\)) and water absorption (\(WA_{24H}\)) were used as performance indicators to identify possible commercial applications for the samples produced. The analysis of the potential of the mixtures considered five different categories of application: (a) high-strength concrete, (b) structural lightweight concrete, (c) non-structural lightweight concrete, lightweight mortars, (d) geotechnical applications and (e) gardening and landscaping ad thermal and acoustic insulation. The methodological approach under discussion is founded upon the findings of preceding studies [6,32].  
However, applying these parameters to many samples tends to result in an exhaustive database that is difficult to understand. Therefore, in order to simplify the presentation of the categorisation parameters and the understanding of the results, the graphical representation of the methodology proposed by [PERSON] [8] was redesigned into a diagram of just two parameters: compressive strength (\(S\)) versus water absorption (\(WA_{24H}\)). This is possible because the particle density criterion is the same for all possible application groups of commercial LWAs (\(\rho d\) less than 2.00 g/cm\({}^{3}\)). As illustrated in Figure 5, the diagram provides a visual representation of the potential commercial LWAs and their respective regions of use.  
\begin{table}
\begin{tabular}{c c c c} \hline \hline
**Determination** & **Method** & **Equation or Parameters** & **References** \\ \hline Water absorption (\(WA_{24H}\)) & Hydrostatic weighing. Sample mass: dry (mA), & \(WA_{24H}=100\) (\(mB-mA\))/\(mA\) (\%) & [50] \\ Particle density (\(\rho d\)) & saturated surface dry (mB) and submerged in & \(\rho d=mA\)/(\(mB-m\)) (\(\mathrm{g/cm^{3}}\)) & [50] \\ Density of dry samples, excluding & water (mC). & \(\rho s=mA\)/(\(mA-m\)) (\(\mathrm{g/cm^{3}}\)) & [50] \\ permeable pores (\(\rho s\)) & Water pycrometry. Pycrometer mass: empty (P1), & & \\ Real density (\(D_{\mathrm{J}}\)) & plus sample (P2), plus sample plus water (P3), plus water (P4), & \(D_{\mathrm{J}}=(P2-P1)\)/[\(\mathrm{f/(P4-P1)}-(P3-P2)\)] (\(\mathrm{g/cm^{3}}\)) & [51] \\ \hline Total porosity (\(P_{\mathrm{J}}\)) & Relationships between Particle density (\(\rho d\)), & \(P_{\mathrm{T}}=100\) [\(1-(\rho d\)/\(D)\)] (\(\%\)) & [52] \\ Open porosity (\(P_{\mathrm{O}}\)) & (pos) and Actual density (Dt). & \(P_{\mathrm{O}}=100\) [\(1-(\rho d\)/\(\rho s)\)] (\(\%\)) & [52] \\ \hline Closed porosity (\(P_{\mathrm{C}}\)) & Difference between Total Porosity (P\(\tau\)) and Open & \(P_{\mathrm{C}}=P_{\mathrm{T}}-P_{\mathrm{O}}\) (\(\%\)) & [52] \\ \hline Bloating Index (\(BI\)) & Variation in the average volume of the particles, & & \\  & from the initial state (V1) to the final state after & \(BI=100\) (\(V2-V1\))/\(V1\) (\(\%\)) & [53] \\ Microstructure (\(SEM\)) & Scanning electron microscopy. Vega-3 LMU & Acceleration voltage of 20 kV. & [54] \\  & TESCA microscope. & & \\ Mineralogy (\(XRD\)) & X-ray diffractometry. Shindzau XRD-7000 & Cu K\(\alpha\) radiation at 40 Ma; 40 kV; 10 to 80\({}^{\circ}\) (20); & [55] \\  & diffractometer. & 0.02\({}^{\circ}\) pitch and 1.20\({}^{\circ}\)/min speed. & [55] \\ \hline Thermal analysis (\(TC\)- \(DTA\)) & Simultaneous thermogravimetric analysis. & 30 \({}^{\circ}\) Cu to 1200 \({}^{\circ}\)/\(\mathrm{c}\) rate of 8\({}^{\circ}\)C/min, nitrogen gas, & [13] \\  & Shimadzu DTG-60 analyser. & isotherm for 15 min. & [56] \\ \hline Loss on ignition (\(LO\)) & Difference between the mass of the samples before & \(LOI=100\) (\(Mi-Mf\))/\(Mi\) (\(\%\)) & [56] \\  & and after sintering. & & \\ \hline Crushing resistance (\(S\)) & Average of the individual strength of the granules. & & \\  & Where, load at failure (\(P_{\mathrm{O}}\)) and particle diameter (\(\mathrm{s}\)). & \(S=2.8P_{\mathrm{O}}/\pi x^{2}\) (MPa) & [57] \\ \hline \hline \end{tabular}
\end{table}
Table 3: Characterisation tests on the samples produced.