## 3 Results and Discussion
### Comprehensive Discussion of Test Results  
In the selection of aggregates for cement concrete, although the mechanical and chemical properties of the aggregate must be considered, its physical properties such as specific gravity, bulk density, and water absorption are also very important. For example, the water absorption or water content of aggregates affects the workability of fresh concrete and affects the strength and durability of hardened concrete. Therefore, the moisture dynamics of the aggregate have a more profound effect than its hardness. In this study, nine kinds of raw material formulations were planned, and the tests of sintering LWAs in high-temperature furnaces were carried out at different sintering temperatures. The obtained results were compared with related literature using sludge as a raw material, as shown in Table 9. It can be seen from Table 9 that the results of the loss on ignition, water absorption rate, and particle density of sintered LWAs in this research were all within the scope of the relevant literature. Figure 16: Appearance of the sintered aggregates of water purification sludge blended with textile sludge from Sample C. \begin{table}
\begin{tabular}{c c c c c c c} \hline \hline \begin{tabular}{c} **Mix No.** \\ \end{tabular} & \begin{tabular}{c} **W/B** \\ \end{tabular} & \begin{tabular}{c} **Water** \\ **(kg/m\({}^{3}\))** \\ \end{tabular} & \begin{tabular}{c} **Cement** \\ **(kg/m\({}^{3}\))** \\ \end{tabular} & \begin{tabular}{c} **Slag** \\ **(kg/m\({}^{3}\))** \\ \end{tabular} & \begin{tabular}{c} **Fly Ash** \\ **(kg/m\({}^{3}\))** \\ \end{tabular} & \
\begin{tabular}{c} **LWA** \\ **(kg/m\({}^{3}\))** \\ \end{tabular} &
\begin{tabular}{c} **FA** \\ **(kg/m\({}^{3}\))** \\ \end{tabular} \\ \hline LC1 & 0.36 & 210 & 350 & 175 & 58 & 370 & 584 \\ LC2 & 0.39 & 210 & 323 & 162 & 54 & 377 & 615 \\ LC3 & 0.43 & 210 & 293 & 147 & 49 & 382 & 649 \\ \hline \hline \end{tabular} Note: W/B, water-binder ratio; LWA, lightweight aggregate; and FA, fine aggregate.  
\end{table} 
Table 8: Mix proportions of the textile-sludge-based lightweight aggregate concrete. The appearance and texture of the LWAs sintered from different raw material formulations were roughly similar, as shown in Figures 14-16. The color of the aggregate was close to reddish brown, which was caused by the change in the valence of ferric ions in the sludge chemical composition at the expansion temperature. In addition, except that the LWAs sintered from Sample C had obvious cracks on the outside, the LWAs sintered from Samples A and B had no obvious cracks, but there were foaming pores inside. Compared with the literature [16; 17; 18], the particle density of the textile-sludge-based LWAs fired in this study was between 0.54 and 1.23 g/cm\({}^{3}\), which was narrow and low. However, the particle density generally met the category of general LWAs. Particle density is the most important physical property of LWAs. Generally, the particle density of normal-weight aggregates is about 2.4-2.7 g/cm\({}^{3}\), and the unit weight of the concrete mixed with it is about 2300-2400 kg/m\({}^{3}\). LWAs can have different particle density requirements depending on the application. Generally, the unit weight of lightweight aggregate concrete must be lower than 2000 kg/m\({}^{3}\), so the corresponding particle density requirements for LWAs must be lower than 1.7-1.8 g/cm\({}^{3}\). If it is applied to non-structural LWAC or thermal insulation LWAC, the particle density of LWAs must be lower than 1.0 g/cm\({}^{3}\). According to the difference in unit weight and strength, ACI divides lightweight concrete into three grades: low-density concretes (0.7-2.0 MPa), moderate-strength concretes (7-14 MPa), and structural concretes (17-63 MPa), as shown in Figure 18 [49]. Low-density concrete is generally used for thermal insulation buildings; medium-strength concrete is often used for concrete blocks and other structures that require a little strength; and structural concrete is used for structures that require strength.