Material Volume Reduction with Additive Manufacturing: Challenges for Structural Application

As the printing speed, the material properties, and the printing quality of additively manufactured concrete, also called 3D printed concrete (3DPC), are vastly improving, the technology is increasingly finding its way towards real-life applications such as dwellings and bridges. However, to reach the technology readiness level this technique is aiming for, two large challenges remain, namely the introduction of reinforcement into 3DPC, and the reduction of volume used to achieve sustainable and visually pleasing structures. The former concerns the application of 3DPC as structural elements that have a certain degree of ductility, and the latter concerns the sustainability of 3DPC, which can only outperform cast concrete in the case of geometrically complex structures where volume is reduced. The current contribution investigates a solution to the reinforcement problem by introducing a hybrid beam system, in which an unreinforced additively manufactured concrete component is combined with a traditionally reinforced cast concrete component to form a functional hybrid 3DPC-cast beam system. A common volume reduction algorithm is applied to the 3DPC component of the hybrid system. A maximum stiffness objective is combined with a volume constraint, after which the structural capacity is determined considering the interface stresses observed for each of the volume-reduced geometries. Herewith, a complex geometry is obtained to be manufactured with 3D concrete printing. A numerical analysis follows in which challenges for structural application, such as loss of bearing capacity and loss of interface bonding are identified and further elaborated.