*6.2. Thermal Conductivity*

The capacity of a substance to transport heat is measured by thermal conductivity, which is significant in determining the insulation of materials. Lightweight concrete normally has low thermal conductivity compared to conventional concrete [3]. The thermal conductivity of lightweight concrete is 0.9567 W/m·K, whereas the thermal conductivity of normal weight aggregate is 1.98–2.94 W/m·K [46]. The low thermal conductivity of lightweight concrete can be due to the type of material used to produce lightweight aggregate. According to Tajra et al. [53], the low conductivity of lightweight concrete is due to the use of expanded perlite as the core structure, which has a low thermal conductivity of about 0.05 W/m·K, as well as the use of expanded perlite powder in the shell structure, which improved its thermal properties. Concrete with lightweight coarse and fine aggregate has the lowest thermal properties, 0.0703 W/m·K, when compared to conventional concrete, which has thermal properties of 1.736 W/m·K [2]. Figure 7 shows the comparison between lightweight aggregate concrete and conventional concrete. Based on Figure 7, the lightweight aggregate concrete had decreased by 95.95% and 67.46% as compared to normal aggregate concrete. The application of sintered expanded slate aggregate in coarse and fine aggregate showed that it had the lowest thermal conductivity. Therefore, it can be concluded that the application of sintered lightweight aggregate in concrete is more suitable to be used as thermal insulation material. It would be fascinating to look into finding the thermal conductivity of concrete using cold-bonded lightweight aggregate and autoclaved lightweight aggregate.

**Figure 7.** Previous studies' comparison on thermal conductivity between lightweight aggregate concrete and conventional concrete.
