Influence of initial molding parameters and natural moisture migration on biochar-based soil composite for thermal backfills applications

Sustainable materials are essential for next generation infrastructures that not only improve their functionality but also have minimal impact on the environment. The application of biochar has been proposed for thermally active structures owing to its lower thermal conductivity (K) and unparalleled carbon stability in recent studies. This study investigates the applicability of the biochar-based soil composite (BbSC) at varying density states (1.1–1.3 Mg m−3), intending to substitute conventionally used granular materials in thermal backfills. The BbSC was prepared by amending the locally available soil with biochar varying from 5 to 15% by weight. The BbSC was prepared in the dry and wet states by varying the molding water content from 10 to 30% at the compaction stage of sample preparation. Later, the K and volumetric heat capacity (C) were examined. Moreover, underground granular backfills might interact with moisture due to groundwater movement and rainfall. Therefore, another set of BbSC samples was injected with water from the bottom to simulate a near-saturation state, and their thermal characteristics were compared. The experiments revealed that the decrease in the thermal conductivities of BbSC upon increment in biochar content is consistent with only up to 10% biochar content. Moreover, K of BbSC increases with the increase in moisture content. From the measured data, linear regression was performed along with the sensitivity analysis to quantify the relationship between thermal characteristics and the initial molding state (dry density, initial water content, and biochar content) for BbSC. The developed equations can be helpful for the geotechnical and environmental engineering community in designing the large-scale application of the BbSC for sustainable thermal backfills.

---

Opracowanie rekordu ze środków MNiSW, umowa nr SONP/SP/546092/2022 w ramach programu "Społeczna odpowiedzialność nauki" - moduł: Popularyzacja nauki i promocja sportu (2024).