High thermal conductivity concrete for energy piles

Abstract

Research is increasingly focusing on thermal properties of concrete with the aim of reducing the heat exchange between buildings and environment. On the other hand, concretes with high thermal conductivity could have interesting applications in the field of thermo-active ground structures as Geothermal Energy Piles (GEPs). This kind of foundations represent an environmentally friendly technology that allows exploiting the heat of the shallow earth surface to supply renewable energy for the air conditioning of buildings. GEPs are needed for structural and geotechnical reasons and allow recovering the installation costs connected to vertical boreholes. Concrete drilled or driven piles are equipped with a Primary Circuit (PC) of high-density polyethylene plastic pipes attached to the reinforcement cages. Thermal energy is extracted from or injected into the ground thought a carrier fluid that flows into the pipes of the PC. To improve the heat exchange between the pile and soil the thermal properties of the concrete should be considered as design parameters. Concrete thermal conductivity, contrary to what happens for the buildings, should be increased to optimise the thermal performance of the GEPs. Different solutions that modify the mix design of concrete are proposed to the aim of increasing the thermal performance of GEPs.