Mechanical and microstructure evolution of 3D printed concrete interlayer at elevated temperatures

As the technology of 3D printed concrete (3DPC) continues to advance in modern construction, understanding its fire resistance becomes increasingly important. Despite this, the performance of 3DPC under elevated temperatures-particularly in the interlayer regions, which are the weakest parts of the structure-has not been thoroughly examined. This study explores the mechanical and microstructural changes occurring in the interlayers of 3DPC when subjected to high temperatures. Through interlayer bond strength tests and advanced techniques, including X-ray Computed Tomography (CT), Scanning Electron Microscopy (SEM), X-ray Diffraction (XRD), and Thermogravimetric Analysis (TGA), it is found that elevated temperatures markedly decrease interlayer strength, leading to significant pore formation and phase transitions. Specifically, interlayer bond strength diminished by 83.1 % at 600 degrees C and exceeded 90 % at 800 degrees C. A notable increase in pore count-up by 35 % at 400 degrees C compared to room temperature-was also recorded. Additionally, mass loss increased significantly, reaching 13.6 % at 800 degrees C. These results indicate substantial degradation of structural integrity, providing critical insights for the development of more fire-resistant 3DPC materials and enhancing fire safety in construction.