On demand additive manufacturing of functionally graded concrete

The rapid development of additive manufacturing of cementitious materials has enabled the emergence of a new design paradigm, namely functional grading of material properties by location. Target performance parameters could be material weight and insulation value or (particularly important) ductility. A generic concept to achieve this, is through the selective addition of fibres or aggregates. In 3D concrete printing (3DCP), this concept can be developed into two strategies: by adding particles (i) to the bulk mixture through a second stage mixing process at the printer head (Simultaneous Process, SP), or (ii) in between the layers of deposited cementitious filament (Repetitive Sequential Process, RSP). The present paper presents the development of specific equipment required to obtain on–demand functional grading of the printed material. Subsequently, the application of these systems in print trials is shown. The current study focussed on ductility by creating fibre–reinforced 3D printed concrete through both strategies. The mechanical performance of the obtained material has been established through compressive, flexural, and crack–mouth opening displacement tests. To underline the generic nature of the strategies, a trial with lightweight aggregates has also been performed. It was shown that particularly the SP is capable of achieving improvements in ductility and self–weight