Systematic Literature Review of the Evaluation of the Thermal Conductivity of 3D Concrete Printed Building Elements

Three-dimensional (3D) concrete printing technology has attracted widespread attention in the building and construction industry. Research studies have shown this technology’s high-speed construction, waste minimization, and design freedom capabilities. However, an accurate and reliable experimental analysis of the thermal behavior of the 3D concrete printed (3DCP) building elements remains poorly understood. Specifically, research works on thermal conductivity and its dependence on geometry, structure, mix composition, and printing parameters are significantly underdeveloped. A comprehensive understanding of this property could be crucial for improving thermal comfort, enhancing energy efficiency, and minimizing building heat loss in printed structures. Therefore, the aim of study aim was to critically examine knowledge on the thermal conductivity of 3DCP elements, paying attention to influential factors and potential improvements in the existing experimental protocols. This systematic literature review uses the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) framework for a reliable and transparent review of records published between 2009 and 2024. Hot box and hot wire experimental setups were identified as the most used experimental techniques based on steady-state and transient conditions, respectively. Thermal conductivity decreases with increased geometric complexity, lower density, and the inclusion of aggregates or phase change materials. Normalized thermal conductivity, with respect to material density, is lower in 3DCP elements versus traditional counterparts. Studies reported an inverse relationship between porosity and thermal conductivity, owing to the effect of air pockets, voids, and hollowness within the structures. For small-scale elements, thermal conductivity is anisotropic, but more evidence is needed to quantify anisotropic effects. We propose a novel and simple experimental protocol to assess anisotropy. The measurement protocol would employ the ISO/ASTM C1363 thermal transmission assessment guidelines recommended under ISO/ASTM 52939 for 3DCP elements. This review contributes toward achieving accuracy and reproducibility in the thermal assessments of 3DCP elements, paying attention to potential anisotropic effects, hence supporting future thermal design efforts with better-performing building envelopes.