Interfacial Properties of Three-Dimensional-Printed Permanent Formwork with Cast-in-Place Concrete

The rapid construction of prefabricated components of reinforced-concrete structures using three-dimensional (3D) printing of concrete as a permanent formwork is a promising way to combine 3D printing organically with traditional construction technology. The bonding property of the contact interface between the 3D-printed permanent formwork and internal postcast concrete is crucial for maintaining the overall mechanical performance of the 3D-printed structure. In this study, the roughness of contour formworks was quantified by using 3D scanning. A large-scale formwork was fabricated by using a robotic 3D printer, and four types of cast-in-place concrete were poured into the formwork to form solid components. The interfacial bonding properties between the formwork and cast material were evaluated by splitting tensile tests and antisymmetric four-point bending shear tests. The interfacial microstructure was analyzed by using computed tomography and scanning electron microscopy. The bond performance can mainly be attributed to the mechanical interlock at the interface between the contour formwork and cast aggregated concrete. The self-compacting concrete with the expansion agent contributes the most to the interface bonding.