Functionally graded lightweight cement-based composites with outstanding mechanical performances via additive manufacturing

Light weight and high strength are contradictory issues for most engineering materials. Through 3D concrete printing (3DCP), functionally graded construction materials can be produced to achieve material economization and outstanding mechanical performances simultaneously. In this paper, cement-based composites exhibiting lamellar microstructures with graded porosity and fiber distribution, were fabricated via depositing cement pastes with different densities and fiber contents at designed positions. Compared with casted homogeneous concrete, printed graded composites demonstrate 75%-92% higher specific bending strength and 2.2 times of specific impact strength. In addition, the specific compressive strength of several graded composites displays 76%-96% increasement when the pressure is parallel to the lamellar structure. Unique failure modes also appear in graded composites, including crack twisting, multiple cracking and compressive anisotropy. Finite element simulations reveal that a rational stress "redistribution" inside the graded composites, which follows the strength distribution of constituent materials, contributes to the superior mechanical performances under light weight for the graded architectures. This work paves a facile and valid way for the design and fabrication of functionally graded cement-based composites, as well as brings great potential and more insights into 3DCP technique.