Mechanical Behavior of Hardened Printed Concrete and the Effect of Cold Joints: An Experimental Investigation.

The adaptation of 3D printing techniques within the construction industry has opened new possibilities for designing and constructing cementitious materials efficiently and flexibly. The layered nature of extrusion-based concrete printing introduces challenges, such as interlayer weaknesses, that compromise structural integrity and mechanical performance. This experimental study investigates the influence of interlayer orientation and the presence of cold joints (CJ) on mechanical properties, such as stiffness and strength. Three-point bending tests (3PBT) and optical measurement techniques are employed to correlate these properties with the structural response of hardened printed concrete. The analysis determines key properties like Young's modulus and flexural tensile strength and evaluates them statistically. The investigation examines crack development and failure mechanisms, relating them to the material properties. The findings reveal a strong dependency of material properties and crack formation on layer orientation. Specimens with interlayers aligned parallel to the loading direction exhibit significantly inferior mechanical properties compared with other orientations. The presence of CJ considerably influences the progression of crack formation. This research contributes to a deeper understanding of the structural performance of printed concrete.