# Experimental Characterization of the Engineering Properties of Landfill Compost-Biocover
## 3 Results and Discussions
### Thermal Behavior of Compost Materials
The experimental data set was validated with the theoretical data set, estimated with the model as reported in [54] and Figure 13; both data sets show close agreement. The model data set shows a slightly higher peak at low water content, and this slight difference is because compost is a combination of various ingredients with different properties. Figure 14 shows that the specific heat of compost material increases with an increase in water content in a linear fashion, similar to [PERSON] et al. [55] and [PERSON] et al. [56]. This is because the specific heat of water (4.18 kJ/kg\(\cdot\)K) is almost four times that of air (1 kJ/kg\(\cdot\)K) [56]. Consequently, a gradual increase in water content increases water-filled pores, therefore reducing the fraction of air-filled pores, consequently increasing the specific heat [38]. Figure 12: Relationship between thermal conductivity and degree of saturation of compost material. Generally, the specific heat of the studied material varies from 1.58 to 4.48 kJ/kg:K for water content variations between 38% and 107% (Figure 14), showing comparatively high values compared to other compost materials; 1.9 kJ/kg:K for soil organic matter [56], 1.40 for sawdust, and 1.57 for oat straw [57], and soils as well; 0.9 for soil minerals, 0.86 for clay, and 0.775 for sandstone [56]. The test data also agree with the findings of [38], in which the specific heat of compost materials, made of cattle manure with sawdust and rice hulls, varied from 1.59 to 3.14 kJ/kg:K. According to [PERSON] et al. [56], soil with high specific heat provides ample heat storage. This means that the studied material comparatively shows a greater tendency to store heat than soils and other compost materials, which may alternately provide a better tendency to maintain a specific temperature within the cover for microbial organisms over the more extended period during winter, preceding the summer season in colder regions. Figure 14: Relationship between specific heat and water content of compost material. Figure 13: Comparison of experimental and theoretical test data of compost material. The thermal diffusivity of compost material, as in Figure 15, increases with an increase in water content, in an almost similar fashion to that of the thermal conductivity profile in Figure 11. The mechanisms responsible for this trend are also the same, which have already been discussed above. It is evident from Figure 15 that the thermal diffusivity varies from 4.0 \(\times\) 10\({}^{-8}\) to 7.96 \(\times\) 10\({}^{-8}\) m\({}^{2}\)/s for variations in water content from 38% to 107%, which is in close agreement with the data set of other compost materials, i.e., silage (1 \(\times\) 10\({}^{-8}\) m\({}^{2}\)/s) [57] and oat straw (6 \(\times\) 10\({}^{-8}\) m\({}^{2}\)/s) [38]. Furthermore, the studied material shows more diffusivity potential than other compacted clays, i.e., 1 \(\times\) 10\({}^{-11}\) for compacted wastewater clay and 3 \(\times\) 10\({}^{-10}\) for kaolinite clay [58]. It can be concluded from test results that the studied material tends to attain thermal equilibrium quickly, spreading heat within the medium faster than other materials. The thermal properties of compost in this study have been examined for initial conditions only. They may therefore change with changes in the extrinsic climatic conditions, intrinsic behavior of biocover, and underlying landfill waste over time. The study suggests a need to simulate the heat transfer between the biocover and the atmosphere and between the biocover and the underlying landfill waste over a longer period for changed conditions.