Bond behavior between steel bars and 3D printed concrete: Effect of concrete rheological property, steel bar diameter and paste coating

• The effects of the rheological property on the steel–concrete bond behavior of printed and cast samples were investigated. • The porosity at the steel–concrete interface is related to the bond strength. • The bond strength values of 3D printed samples with ribbed bars of different diameters were compared. • The rheological properties of fresh concrete for 3D printing are very significant to control the quality of reinforced 3D printed concrete. Due to the unique layer by layer deposition process of extrusion-based 3D printed concrete (3DPC), the bonding of steel bars with 3DPC differs from that with traditional cast concrete. To understand the steel-printed concrete bond behavior, this paper mainly explored the effect of preparation technologies, concrete rheological properties, steel bar diameter and paste coating on steel bars on the bond behavior between ribbed steel bars and concrete. According to pull-out test and X-ray computed tomography test, the results showed that bond strengths between 3DPC and steel bars were obviously lower than those between steel bars and cast concrete. The rheological properties of fresh concrete show significant impact on the bond behavior of reinforced 3D printed samples. Lower yield stress and plastic viscosity can narrow the bond strength gap between printed samples and cast samples. The utilization of surface coated steel bar with fresh cement paste can effectively enhance the steel-3DPC bond strength. The variations in steel–concrete bond strengths can be explained via pore structure at steel–concrete interface. The results suggest that it is of great importance to control the quality of reinforced 3D printed concrete by optimizing the rheological properties of fresh concrete for 3D printing.