Influences of particle size on the performance of 3D printed coarse aggregate concrete: Experiment, microstructure, and mechanism analysis

Compared with traditional construction technology for building structures, three-dimensional (3D) printed concrete (3DPC) technology offers significant advantages. However, current 3DPC use in engineering applications predominantly relies on mortar, which suffers from significant shrinkage and cracking. To overcome the shortcomings, this study incorporated coarse aggregates into 3DPC and clarified the influence of various sized aggregates on the fresh and hardened performance of 3D printed coarse aggregate concrete (3DPCAC). Experimental research on 3DPCAC was conducted, and the effects of different particle sizes of coarse aggregates on workability were determined. It was found that as size increases, the extrudability decreases, stability improves, and slump reduces. These effects were explained through rheological analysis. As particle size increases, static yield stress rises, while dynamic yield stress increases slightly. Mechanical tests were also conducted to characterise the effects of particle size and loading directions on the performance of 3DPC. The results show that as aggregate particle size increases, the mechanical properties of 3DPC improve and all groups exhibit significant anisotropy. Additionally, microscopic tests revealed that the pores of 3DPC exhibited directionality, explaining the anisotropy through fracture mechanics analysis. Overall, large coarse aggregates significantly enhance the compressive strength and elastic modulus of 3DPCAC. However, they may reduce extrudability and increase anisotropy.