Effect of Delay-Time on the Mechanical Properties of Extrusion-Based 3D Printed Concrete (2017-07)¶

The extrusion-based 3D printing method is one of the main additive manufacturing techniques used in the construction industry which is capable of producing large-scale building components with complex geometries without the use of the expensive formwork. The mechanical properties of the printed concrete component are very much unlike the conventionally cast concrete. Therefore, the properties of these are important for the design of structures built with 3D printing process. In this study, a custom-made apparatus was used to simulate extrusion-based 3D printing process. Layered specimens with 10, 20 and 30 minutes delay time (i.e. the printing time interval between layers) have been printed using tailored conventional concrete mixture. Mechanical properties including compressive, flexural and inter-layer bonding strengths have been measured and the effect of delay time on the mechanical properties has been investigated. All printed specimens exhibited an anisotropic phenomenon in both compressive and flexural strengths. A significant inverted bell curve pattern emerged in the inter-layer bonding strength. The inter-layer bonding strength of the specimens with 10 minutes and 30 minutes delay time was similar, but higher than that of specimen with 20 minutes delay time. The major finding is that the surface moisture content plays a major role in the inter-layer bonding strength.