Thermal and mechanical performance of 3D printing functionally graded concrete: The role of SAC on the rheology and phase evolution of 3DPC

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In order to address the dual objectives of enhancing the mechanical and thermal performance of 3D printed concrete, this paper presents a 3D printing approach to design and prepare functional graded concrete for energy-saving sandwich structures with both thermal insulation and load-bearing functions. The 3D printing functionally graded concrete (3DPFGC) with a sandwich structure, consists of an expanded polystyrene concrete inner layer and a 3D printed concrete outer layer. In addition to the three-dimensional compressive strength and double-shearing tests, the thermal conductivity of 3DPFGC was also measured by steady-state method and compared with the transient method and verified by theoretical formulas. The influence of sulphoaluminate cement on the printability of the load-bearing layer was also comprehensively investigated by calorimetry test, rheological test, XRD and TG analysis. The addition of SAC has a significant impact on the early fresh properties, including accelerating the setting time and optimizing the rheological properties, directly improving the printing performance. 3DPFGC exhibits significantly higher compressive strength compared with other lightweight insulating concrete with similar thermal conductivities. The outcome of this research provides valuable guidance for the application of 3DPFGC in building engineering, contributing to the development of energy-efficient and structural construction materials.