Energy micropiles are deep foundation structures designed to exchange heat between the soil and the building using the shallow geothermal energy. This research shows both experimental tests and numerical simulations dealing with the thermal performance of energy micropiles. Different types of cement–based grouts, with or without chemical additives used to increase their thermal conductivity, were experimentally tested. Thermal conductivity tests, workability tests and mechanical strength tests were performed on liquid and on hardened grouts prepared at different water/cement ratios. The greatest thermal conductivity increase (about 19%) was measured when a graphite–based additive was used at 10% concentration and water/cement ratio of 0.30. Thermal diffusivity and volume heat capacity were not significantly affected by the presence of additives. The initial viscosity of the enhanced grouts was reduced when additives were used, while the mechanical performance was comparable to that of the neat mortar. Experimental data were used to calibrate the finite element numerical model simulating 3D, transient heat transfer process for an energy micropile part of a large foundation raft. The effects of thermal properties of construction materials, mass flow rate of the heat–carrier fluid and spacing among energy micropiles were analyzed. As a result, the thermal performance and efficiency of the system were significantly affected by the mass flow rate magnitude and by spacing, while the exchanged thermal power was slightly affected by the increase of the thermal conductivity of the used materials.

Experimental and numerical study on the thermal properties of cement–based grouts for energy micropiles

Giovanni Ciardi
;
Claudio Tamagnini
2024

Abstract

Energy micropiles are deep foundation structures designed to exchange heat between the soil and the building using the shallow geothermal energy. This research shows both experimental tests and numerical simulations dealing with the thermal performance of energy micropiles. Different types of cement–based grouts, with or without chemical additives used to increase their thermal conductivity, were experimentally tested. Thermal conductivity tests, workability tests and mechanical strength tests were performed on liquid and on hardened grouts prepared at different water/cement ratios. The greatest thermal conductivity increase (about 19%) was measured when a graphite–based additive was used at 10% concentration and water/cement ratio of 0.30. Thermal diffusivity and volume heat capacity were not significantly affected by the presence of additives. The initial viscosity of the enhanced grouts was reduced when additives were used, while the mechanical performance was comparable to that of the neat mortar. Experimental data were used to calibrate the finite element numerical model simulating 3D, transient heat transfer process for an energy micropile part of a large foundation raft. The effects of thermal properties of construction materials, mass flow rate of the heat–carrier fluid and spacing among energy micropiles were analyzed. As a result, the thermal performance and efficiency of the system were significantly affected by the mass flow rate magnitude and by spacing, while the exchanged thermal power was slightly affected by the increase of the thermal conductivity of the used materials.
2024
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Utilizza questo identificativo per citare o creare un link a questo documento: https://hdl.handle.net/11391/1589814
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