Improvement of Soil Thermal Conductivity with Graphite-Based Conductive Cement Grouts
Publication: Journal of Geotechnical and Geoenvironmental Engineering
Volume 150, Issue 10
Abstract
Shallow geothermal energy systems (SGES) are a promising technology for contributing to the decarbonization of the energy sector. Soil thermal conductivity () governs the heat transfer process in ground under a steady state; thereby, it is a key parameter for SGES performance. Soil mixing technology has been successful in enhancing the shear strength of soils, but is adopted in this paper for the first time to improve soils as a geothermal energy conductive medium for SGES applications. First, the thermal conductivity of six types of soils was systematically investigated and the key parameters analyzed. Next, graphite-based conductive cement grout was developed and mixed with the six soils in a controlled laboratory setting to demonstrate the significant increase in soil thermal conductivity. For example, the thermal conductivity of a very silty dry sand increased from 0.19 to (a remarkable 14-fold increase) when mixed with the conductive grout at a soil-to-grout ratio of . In addition, the mechanical properties of the cement grouts and cement-mixed soils were examined along with the microstructural analysis, revealing the mechanism behind the thermal conductivity improvement.
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Data Availability Statement
All data, models, and code generated or used during the study appear in the published article.
Acknowledgments
This research was funded by the EPSRC program grant SaFEGround—Sustainable, Flexible and Efficient Ground-source heating and cooling systems (EP/V042149/1), and Royal Academy of Engineering Research Fellowship (RF2223-22-118).
References
Allan, M. L., and S. P. Kavanaugh. 1999. “Thermal conductivity of cementitious grouts and impact on heat exchanger length design for ground source heat pumps.” HVAC&R Res. 5 (2): 85–96. https://doi.org/10.1080/10789669.1999.10391226.
Ashour, T., A. Korjenic, S. Korjenic, and W. Wu. 2015. “Thermal conductivity of unfired earth bricks reinforced by agricultural wastes with cement and gypsum.” Energy Build. 104 (Apr): 139–146. https://doi.org/10.1016/j.enbuild.2015.07.016.
ASTM. 2017. Standard test method for unconfined compressive strength of cohesive soil. ASTM D2166. West Conshohocken, PA: ASTM.
ASTM. 2022. Standard test method for determination of thermal conductivity of soil and soft rock by thermal needle probe procedure. ASTM D5334. West Conshohocken, PA: ASTM.
Barry-Macaulay, D., A. Bouazza, R. M. Singh, B. Wang, and P. G. Ranjith. 2013. “Thermal conductivity of soils and rocks from the Melbourne (Australia) region.” Eng. Geol. 164 (Aug): 131–138. https://doi.org/10.1016/j.enggeo.2013.06.014.
Barry-Macaulay, D., A. Bouazza, B. Wang, and R. M. Singh. 2015. “Evaluation of soil thermal conductivity models.” Can. Geotech. J. 52 (11): 1892–1900. https://doi.org/10.1139/cgj-2014-0518.
Bentz, D. P., and P. E. Stutzman. 2006. “Curing, hydration, and microstructure of cement paste.” ACI Mater. J. 103 (5): 348.
Blazquez, C. S., A. F. Martín, I. M. Nieto, P. C. Garcia, L. S. S. Perez, and D. Gonzalez-Aguilera. 2017. “Analysis and study of different grouting materials in vertical geothermal closed-loop systems.” Renewable Energy 114 (Dec): 1189–1200. https://doi.org/10.1016/j.renene.2017.08.011.
BSI (British Standard Institution). 2011. Cement composition, specifications and conformity criteria for common cements. BS EN 197-1:2011. London: BSI.
BSI (British Standard Institution). 2021. Cement portland-composite cement CEM II/C-M and composite cement CEM VI. BS EN 197-5:2021. London: BSI.
Carlsten, P., and J. E. Ekstrom. 1997. Lime and lime cement columns: Guide for project planning, construction and inspection. Linköping, Sweden: Swedish Geotechnical Society.
Delaleux, F., X. Py, R. Olives, and A. Dominguez. 2012. “Enhancement of geothermal borehole heat exchangers performances by improvement of bentonite grouts conductivity.” Appl. Therm. Eng. 33 (Apr): 92–99. https://doi.org/10.1016/j.applthermaleng.2011.09.017.
Do, T. M., H. K. Kim, M. J. Kim, and Y. S. Kim. 2020. “Utilization of controlled low strength material (CLSM) as a novel grout for geothermal systems: Laboratory and field experiments.” J. Build. Eng. 29 (Jun): 101110. https://doi.org/10.1016/j.jobe.2019.101110.
Erol, S., and B. Francois. 2014. “Efficiency of various grouting materials for borehole heat exchangers.” Appl. Therm. Eng. 70 (1): 788–799. https://doi.org/10.1016/j.applthermaleng.2014.05.034.
Farouki, O. T. 1965. “Physical properties of granular materials.” Soil Sci. 99 (5): 354. https://doi.org/10.1097/00010694-196505000-00011.
Fei, W., and G. A. Narsilio. 2022. “Estimation of thermal conductivity of cemented sands using thermal network models.” J. Rock Mech. Geotech. Eng. 14 (1): 210–218. https://doi.org/10.1016/j.jrmge.2021.08.008.
Gopakumar, T. G., and D. J. Y. S. Page. 2004. “Polypropylene/graphite nanocomposites by thermo-kinetic mixing.” Polym. Eng. Sci. 44 (6): 1162–1169. https://doi.org/10.1002/pen.20109.
Gu, X., N. Makasis, Y. Motamedi, G. A. Narsilio, A. Arulrajah, and S. Horpibulsuk. 2022. “Geothermal pavements: Field observations, numerical modelling and long-term performance.” Géotechnique 72 (9): 832–846. https://doi.org/10.1680/jgeot.20.P.296.
Haigh, S. K. 2012. “Thermal conductivity of sands.” Géotechnique 62 (7): 617–625. https://doi.org/10.1680/geot.11.P.043.
Han, C., and X. B. Yu. 2016. “Sensitivity analysis of a vertical geothermal heat pump system.” Appl. Energy 170 (Jun): 148–160. https://doi.org/10.1016/j.apenergy.2016.02.085.
Horpibulsuk, S., R. Rachan, A. Chinkulkijniwat, Y. Raksachon, and A. Suddeepong. 2010. “Analysis of strength development in cement-stabilized silty clay from microstructural considerations.” Constr. Build. Mater. 24 (10): 2011–2021. https://doi.org/10.1016/j.conbuildmat.2010.03.011.
Kim, Y. S., B. H. Dinh, T. M. Do, and G. O. Kang. 2020. “Development of thermally enhanced controlled low-strength material incorporating different types of steel-making slag for ground-source heat pump system.” Renewable Energy 150 (Apr): 116–127. https://doi.org/10.1016/j.renene.2019.12.129.
Kurevija, T., M. Macenic, and S. Borovic. 2017. “Impact of grout thermal conductivity on the long-term efficiency of the ground-source heat pump system.” Sustainable Cities Soc. 31 (May): 1–11. https://doi.org/10.1016/j.scs.2017.02.009.
Laloui, L., and A. R. Loria. 2019. Analysis and design of energy geostructures: Theoretical essentials and practical application. Cambridge, MA: Academic Press.
Liu, L., H. He, M. Dyck, and J. Lv. 2021. “Modeling thermal conductivity of clays: A review and evaluation of 28 predictive models.” Eng. Geol. 288 (Jun): 106107. https://doi.org/10.1016/j.enggeo.2021.106107.
Lu, S., T. Ren, Y. Gong, and R. Horton. 2007. “An improved model for predicting soil thermal conductivity from water content at room temperature.” Soil Sci. Soc. Am. J. 71 (1): 8–14. https://doi.org/10.2136/sssaj2006.0041.
Mahmoud, M., M. Ramadan, K. Pullen, M. A. Abdelkareem, T. Wilberforce, A. G. Olabi, and S. Naher. 2021. “A review of grout materials in geothermal energy applications.” Int. J. Thermofluids 10 (Feb): 100070. https://doi.org/10.1016/j.ijft.2021.100070.
Midttomme, K., E. Roaldset, and P. Aagaard. 1998. “Thermal conductivity of selected claystones and mudstones from England.” Clay Miner. 33 (1): 131–145. https://doi.org/10.1180/000985598545327.
Mitra, A. 2011. “The Taguchi method.” Wiley Interdiscip. Rev. Comput. Stat. 3 (5): 472–480. https://doi.org/10.1002/wics.169.
MPA (Mineral Products Association). 2019. MPA factsheet 18: Embodied CO2e of UK cement, additions and cementitious materials. London: MPA.
Ochsner, T. E., R. Horton, and T. Ren. 2001. “A new perspective on soil thermal properties.” Soil Sci. Soc. Am. J. 65 (6): 1641–1647. https://doi.org/10.2136/sssaj2001.1641.
Preene, M., and W. Powrie. 2009. “Ground energy systems: From analysis to geotechnical design.” Géotechnique 59 (3): 261–271. https://doi.org/10.1680/geot.2009.59.3.261.
Rew, Y., X. Shi, K. Choi, and P. Park. 2018. “Structural design and lifecycle assessment of heated pavement using conductive asphalt.” J. Infrastruct. Syst. 24 (3): 04018019. https://doi.org/10.1061/(ASCE)IS.1943-555X.0000440.
Riemer, M. F., R. B. Seed, P. G. Nicholson, and H. L. Jong. 1990. “Steady state testing of loose sands: Limiting minimum density.” J. Geotech. Eng. 116 (2): 332–337. https://doi.org/10.1061/(ASCE)0733-9410(1990)116:2(332).
Sargent, P., P. N. Hughes, and M. Rouainia. 2016. “A new low carbon cementitious binder for stabilising weak ground conditions through deep soil mixing.” Soils Found. 56 (6): 1021–1034. https://doi.org/10.1016/j.sandf.2016.11.007.
Song, X., R. Zheng, R. Li, G. Li, B. Sun, Y. Shi, G. Wang, and S. Zhou. 2019. “Study on thermal conductivity of cement with thermal conductive materials in geothermal well.” Geothermics 81 (Sep): 1–11. https://doi.org/10.1016/j.geothermics.2019.04.001.
Taki, O., and D. Yang. 1991. “Soil–cement mixed wall technique.” In Proc., Geotechnical Engineering Congress—1991, edited by F. G. McLean, D. A. Campbell, and D. W. Harris, 298–309. New York: ASCE.
Wang, D., Q. Wang, and Z. Huang. 2019. “Investigation on the poor fluidity of electrically conductive cement-graphite paste: Experiment and simulation.” Mater. Des. 169 (Mar): 107679. https://doi.org/10.1016/j.matdes.2019.107679.
Zhang, L., A. Gustavsen, B. P. Jelle, L. Yang, T. Gao, and Y. Wang. 2017. “Thermal conductivity of cement stabilized earth blocks.” Constr. Build. Mater. 151 (Jun): 504–511. https://doi.org/10.1016/j.conbuildmat.2017.06.047.
Zhang, N., and Z. Wang. 2017. “Review of soil thermal conductivity and predictive models.” Int. J. Therm. Sci. 117 (Sep): 172–183. https://doi.org/10.1016/j.ijthermalsci.2017.03.013.
Zhao, Y., X. Chen, T. Wen, P. Wang, and W. Li. 2022. “Experimental investigations of hydraulic and mechanical properties of granite residual soil improved with cement addition.” Constr. Build. Mater. 318 (Jun): 126016. https://doi.org/10.1016/j.conbuildmat.2021.126016.
Information & Authors
Information
Published In
Journal of Geotechnical and Geoenvironmental Engineering
Volume 150 • Issue 10 • October 2024
Copyright
© 2024 American Society of Civil Engineers.
History
Received: Jun 1, 2023
Accepted: May 6, 2024
Published online: Jul 25, 2024
Published in print: Oct 1, 2024
Discussion open until: Dec 25, 2024
ASCE Technical Topics:
- Construction engineering
- Construction methods
- Energy engineering
- Energy sources (by type)
- Engineering materials (by type)
- Engineering mechanics
- Foundation construction
- Foundations
- Geomechanics
- Geotechnical engineering
- Grouting
- Material mechanics
- Material properties
- Materials engineering
- Renewable energy
- Soil cement
- Soil dynamics
- Soil grouting
- Soil mechanics
- Soil mixing
- Soil properties
- Soil stabilization
- Soil strength
- Thermal power
- Thermal properties
- Thermodynamics
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