Influence of Nozzle Diameter on the Anisotropy of Compressive Strength – Measured on 3D Printing Concrete Designed with Recycled Fine Aggregates

3D printing concrete (3DPC) is an innovative method in the construction sector, eliminating the need for traditional formwork. This study introduces a mortar mixed design with recycled fine aggregates (RFA) where dmax < 2 mm. The mortar was printed with two different printers, each equipped with nozzles of different diameters (2 cm and 4 cm). The layers were printed and pressed to widen the string to the chosen width of 6 cm. The primary objective is to study the influence of nozzle diameters on the mechanical properties as well as the anisotropic behavior of 3DPC. The investigation was conducted through mechanical testing on different orientations of printed layers, parallel (oz) and perpendicular (ox) to the printing direction. Results reveal a significant drop of compressive strength in the orientation (oz) when using a 2 cm nozzle compared to a 4 cm nozzle from the same mix design. This is attributed to the intense compression of each layer during deposition to ensure controlled spreading of the material path consequently creating damage in the outer parts of the printed concrete.