# Experimental Characterization of the Engineering Properties of Landfill Compost-Biocover
## 3 Results and Discussions
### Thermal Behavior of Compost Materials  
Figure 11 shows the compost material's thermal conductivity (\(\lambda\)) with the compaction curve. As in Figure 11, the thermal conductivity increases almost linearly for the dry optimum, whereas the rate of increase is minimal for the wet optimum. The dry unit weight increases with increased water content for the dry optimum, resulting in close interaction among compost particles. According to [PERSON]'s law, the conduction of heat is a function of contact surface area [47], and as the compost particles come in close interaction, they gradually decrease in free air space (Figure 8). The contact surface area alternately increases, which increases the conduction of heat, and correspondingly, the thermal conductivity increases [3], or it can be said that the increase in thermal conductivity is also because the thermal conductivity of water (0.6) is approximately 25 times more than that of air (0.024). Other studies, such as [PERSON] et al. [30], showed that the thermal conductivity of compost materials is a function of dry density and a linear relationship exists between the degree of saturation and thermal conductivity. However, in this study, as in Figures 11 and 12, the studied materials provide a linear relationship between thermal conductivity and dry density up to optimal water content, but after this point, the relationship is nonlinear. However, [PERSON] and [PERSON] [38] revealed a linear relationship between water content and thermal conductivity. Furthermore, [PERSON] and [PERSON] [48] reported that the thermal conductivity increased with an increase in water content, as well as with dry unit weight for compacted MX80 bentonite specimens. For the wet optimum, the compost particles are almost saturated with a sufficient addition of water (Figure 7), and due to a high degree of saturation, the added water dilutes/reduces the concentration of soil solids per unit volume, which results in a decrease in the contact surface area and particle-to-particle interactions. Now, the thermal conductivity of water (0.59 w/m\(\cdot\)K) is smaller than that of mineral soil particles, i.e., 2.9 for silt and clay, 3 for sandstone, and 3.8 for dolostone [49; 50], due to which, the rate of increase in the thermal conductivity is minimal for this segment as water dominates the process of heat conduction. The test data show a similar trend as in [51]. Figure 11: Thermal conductivity vs. compaction curve of compost material. Figure 12 provides a clearer picture of the test data. The material shows abrupt changes in thermal conductivity at a high degree of saturation, i.e., close to saturation, and the rate of increase in \(\lambda\) is quite high. [PERSON] [52] reports that the thermal conductivity of the compost materials is relatively low when compared to that of the mineral soils, i.e., 2.9 for silt and clay, 3 for sandstone [49], and 2.74 for sandy loam [38], and as depicted in Figure 11, the thermal conductivity of studied materials generally varies between 0.12 and 0.53 \(\mathrm{w/m\cdot K}\) for changes in water content from 38% to 107%. The general trend is almost similar to sludge compost, for which \(\lambda\) varies from 0.218 to 0.815 \(\mathrm{w/m\cdot K}\)[38], and the slight differences are generally due to a difference in the degree of saturation and biodegradable materials. The compost materials tend to conduct heat at a low rate, providing more heat retention capacity than other mineral materials [52]. Consequently, during the winter season, when the atmospheric temperature is low, this low thermal conductivity enables it to sustain a stable temperature for the activities of the microbial organisms, which therefore extends the CH\({}_{4}\) oxidation process right through a long period in the winter, similar to the findings in [53], which means that the compost materials can effectively be used as landfill cover materials for CH\({}_{4}\) oxidation purposes.