Thermophysical properties under different hygroscopic conditions of an innovative composite concrete pre-walls system.

• Pre-walls system: two pre-cast concrete panels and a cast-in-situ concrete core. • High performance pre-cast concrete and low-cement lightweight cast-in-situ concrete. • Thermophysical properties of concretes for dry, hygroscopic and capillary ranges. • An application study of the pre-walls system to a swimming pool was carried out. • Low-cement lightweight concrete in the core improve the system thermal performance. An innovative system of pre-cast high performance concrete pre-walls, combined with low-cement cast-in-situ lightweight concrete core, is studied experimentally from the standpoint of the thermophysical properties of the concrete compositions under various hygroscopic conditions. Thermal conductivity, volumetric heat capacity and thermal diffusivity are experimentally determined, by a transient method, for eight concrete compositions in the dry state, hygroscopic and over-hygroscopic ranges. The incorporation of lightweight aggregates in the concrete mixture allowed to reduce the thermal conductivity (up to 53%) and thermal diffusivity (up to 41%), in comparison to normal weight concrete. The moisture content, regardless of the composition of the concrete, impacts negatively the thermal performance, with a rise of both thermal conductivity and diffusivity, which was also captured by analytical expressions. An application study of the pre-walls system to a swimming pool showed reductions of thermal conductance of up to 38% when combining high mechanical performance concrete in the pre-walls with lightweight aggregate concrete with high thermal performance in the core. These results highlight the importance of assessing thermophysical properties in service conditions, with the moisture content effect included, and selecting the types of concrete in composite pre-walls systems to enhance both mechanical and thermal performance. [ABSTRACT FROM AUTHOR]