3D printing with concrete is primarily achieved through an extrusion process, where the material is precisely deposited layer by layer to construct structures. Proper control of extrusion ensures consistent material flow, accurate layer formation, and the overall stability of the 3D-printed structure. However, clogging during the extrusion process can occur as the nozzle size is too small relative to the aggregate size. To fundamentally understand the clogging mechanism and optimize the extrusion process, a precise two-phase discrete element model was established to simulate the extrusion process. A cluster of particles was used to model fresh concrete, with hard cores representing the aggregates and concentric soft shells representing fresh cement paste surrounding them. Five nozzles with different outlet diameters were designed and 3D printable concrete with different fineness modulus levels was formulated. The parameters of the two-phase discrete element model were determined based on rheological properties and calibrated using slump flow test results. The simulation results showed good agreement with the experimental pressure values and the quality of extruded filaments. Based on these results, it suggested that ensuring a proper balance between the aggregate fineness modulus and the outlet diameter of printing nozzles is essential for the extrusion process.

中文翻译：

---

3D 可打印混凝土作为两相离散流的可挤压性分析


混凝土 3D 打印主要通过挤压工艺实现，其中材料被精确逐层沉积以构建结构。对挤出的适当控制可确保一致的材料流动、准确的层形成以及 3D 打印结构的整体稳定性。然而，由于喷嘴尺寸相对于骨料尺寸太小，因此在挤出过程中可能会发生堵塞。为了从根本上了解堵塞机理并优化挤出过程，建立了精确的两相离散元模型来模拟挤出过程。一组颗粒用于模拟新混凝土，硬核代表骨料，同心软壳代表它们周围的新鲜水泥浆。设计了五个不同出口直径的喷嘴，并配制了具有不同细度模量水平的 3D 可打印混凝土。两相离散元模型的参数是根据流变特性确定的，并使用坍落度流测试结果进行校准。模拟结果表明，实验压力值和挤出细丝的质量具有良好的一致性。基于这些结果，它表明确保总细度模量和打印喷嘴出口直径之间的适当平衡对于挤出过程至关重要。