Interfacial bonding properties of 3D printed permanent formwork with the post-casted concrete

Abstract

The rapid construction of prefabricated components of reinforced concrete structures using 3D printing concrete as a permanent formwork is a promising way to organically combine 3D printing with traditional construction technology. The bonding property of the contact interface between the 3D-printed permanent formwork and internal post-cast concrete is crucial for the 3D-printed structure to maintain the overall mechanical performance. In this study, the roughness of 3D-printed formwork (10 mm, 15 mm, 20 mm) and the age difference between the formwork and post-cast concrete (1 d, 3 d, 7 d, and 14 d) were set as variables to investigate their influence on the interfacial tensile and shearing bonding properties. Additionally, computerised tomography (CT) scanning was used to visualise the meso-structure of the interfacial zones and the pore characteristics were quantified. The microstructure and hydration products of the bonding interface were detected, and the gradient structure of the interface transition zone of the 3D printing formwork was presented. A plastic limit analytical mechanical model of the interfacial shear strength was established. The results show that the tensile and shear properties of the bonding interface were the best when the layer height of the printing formwork was 20 mm, and it is recommended to cast internal concrete materials after 7 d of 3D printing formwork moulding.