3D printable strain hardening cementitious composites (3DP-SHCC), tailoring fresh and hardened state properties

Abstract

With the introduction of 3D concrete printing, research started on how to include reinforcement in 3D printed structures. Initial studies on the implementation of strain hardening cementitious composites (SHCC) as self-reinforcing printable mortars have shown promising results. The development of this new type of SHCC comes with additional challenges. Where SHCC by itself is already a complex material engineered to achieve specific micromechanical behaviour under tensile loading, its application in 3D printing techniques imposes even more requirements - the so-called ‘printability’ requirements. The question that rises for the development of this new material is how to achieve printability without losing strain hardening capacity. This paper investigates the influence of raw materials and additives, such as silica fume, limestone powder, viscosity modifying agents and water, on the fresh and hardened mechanical properties of printable SHCC, by improving on a previously developed mixture. The fresh material mixtures were subjected to slump flow tests to analyse their applicability for 3D printing. In hardened state, the mixtures were tested on their compressive strength and flexural strength to assess their potential for strain hardening capacity. Finally, two mixtures were selected for printing. The mixtures were assessed on print quality and buildability by the deployment of a buildability test. Furthermore, the printed elements were mechanically tested at 28 days, on compressive strength, flexural strength and uniaxial tensile strength and strain. It was concluded that the silica fume content and water to solid ratio are relevant variables for 3DP-SHCC optimization. The study has yielded two 3DP-SHCC mix designs that display significant strain hardening capacity and good printability properties.