Anisotropic Mechanical Properties of 3D Printed Mortar Determined by Standard Flexural and Compression-Test and Acoustic Emission (2024-11)¶

The mechanical properties of hardened 3D-printed compounds are an important factor for the future design of such structures. The disparities between casted and 3D-printed concrete can be attributed to variations in compaction levels and the multi-layered nature of the entire system. Both of these issues can influence the mechanical properties of the final element. Additionally, the printing process may be hindered by the composition of the mixture, particularly when fibers are present, as they can alter the pump output and the relationship between layers. This paper discusses the impact of different layer compositions and two types of mixes on the mechanical properties of 3D-printed elements. The study explores two types of layer compositions (linear and pyramid) and three-layer amounts (3 layers, 4 layers, and 5 layers). Furthermore, two types of mixes were considered: one without fibers and one with fibers. Acoustic emission techniques were employed to investigate the entire failure process, including the occurrence of cracks. Moreover, fundamental acoustic parameters were established for 3D-printed elements. The research demonstrates that layer distribution and the number of layers do not significantly affect mechanical properties. However, the mechanical properties can be altered by up to 29.6 % based on the loading direction of the specimens. Furthermore, statistically insignificant differences were observed in the resonant frequency and ultrasonic pulse velocity between printed and casted specimens. Lastly, the majority of cracks in the reference specimens were found in the middle, whereas for multi-layered printed specimens, cracks occurred not only in the center but also at a distance from it. This phenomenon shows that printed specimens fail in different ways than ordinary ones. For this purpose, the eccentric cracking coefficient was designed, which can be used to describe the intensity of eccentric cracking in 3D printed specimens.