Hardened properties of 3D printed concrete: The influence of process parameters on interlayer adhesion

The technology of 3D Concrete Printing (3DCP) has progressed rapidly over the last years. With the aim to realize both buildings and civil works, the need for reliable mechanical properties of printed concrete grows. As a consequence of the additive manufacturing technique, 3D printed structures may consist of several layers that should exhibit bond to guarantee a safe structural design. This paper presents the results of an experimental study on the relation between the 3DCP process parameters and the bond strength of 3D printed concrete. The effect of 3 process parameters (interlayer interval time, nozzle height, and surface dehydration) on two mechanical properties (compressive strength and tensile strength, determined through flexural and splitting tests), has been established, in three perpendicular directions. A very limited influence of layer orientation was found for the given process-material combination, given a sufficiently short interlayer interval time. However, the bond strength between the layers reduced for increasing interlayer interval times. This was also reflected by the failure mode of the samples. The reduction in strength became more pronounced for the samples that were left uncovered during the interval time, exposed to drying. No clear relation was found between the height of the nozzle, and the bond strength between layers. The results of this study, in comparison to various other works on 3DCP, emphasize the need for standardization of test methods and characterization of 3D printed concrete, as individual process parameters clearly must be considered in relation to the applied material and other process parameters.