High Thermal Conductivity Concrete for Energy Piles

. 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. Geothermal Energy Piles (GEPs), a kind of thermo-active ground structures, represent an environmentally friendly technology that allows to exploit the low-grade heat energy present in the shallow earth surface in order to supply renewable energy for the air conditioning of buildings. GEPs are needed for structural and geotechnical reasons and allow to recover the installation costs connected to vertical boreholes. Concrete drilled or driven piles, that represent the majority of GEPs, are equipped with a primary circuit (PC) of high-density polyethylene plastic pipes installed into the piles and 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. In order to improve the heat exchange between the pile and the surrounding soil the thermal properties of the concrete should be considered as a design parameter. Concrete thermal conductivity, contrary to what happens for the super-structure, should be increased to optimise the thermal performance of the piles as heat exchangers. Different solutions that modifies the mix design of concrete are proposed to the aim of increasing the thermal performance of GEPs.