Thermal and Mechanical Properties of 3D Printed Functionally Graded Concrete (2025-06)¶

Three-dimensional printed functionally graded concrete (3D-FGC) represents a viable approach for integrating structural and functional elements through tailored material distributions. Two gradient configurations were developed using recycled aggregates (RAs) and polyethylene (PE) fibres. We systematically investigated the printability, mechanical properties, and thermal conductivity of 3D-FGC, supported by microstructural analysis. The findings seek to elucidate the potential mechanisms of impact related to diverse material distributions. The results show that the linear gradient effectively positions the fibres in the tensile zone, resulting in a significant increase in flexural properties and material efficiency, with a peak flexural strength of 6.0 MPa and a thermal conductivity of 0.61 W·m-1·K-1. The liner gradient (LG) specimens exhibited higher porosity (8.38%) and rougher pore surfaces compared to sandwich gradient (SG) samples. Microcracks with reduced widths (from 1.8 μm to 0.8 μm in fiber-reinforced regions) were observed, alongside weak interfacial transition zones (ITZ) between recycled aggregate (RA) and cement. The LG specimen exhibits a multi-stage crack pattern, with densely distributed cracks appearing in the tensile region, which is a primary contributor to enhanced bending performance. The gradient designs demonstrate strong potential for applications requiring tailored mechanical and thermal properties, such as prefabricated and on-site printed structural elements. In conclusion, this work paves the way for innovative design strategies in the additive manufacturing of functionally graded concrete.