Steel cable bonding in fresh mortar and 3D printed beam flexural behavior

This paper presents an approach for enhancing the path-following capability of concrete printing by integrating steel cables into the center of printed mortar strips during the print process, thus satisfying the synchronous and continuous requirements of 3D printing construction. To investigate the impact of steel cables on buildability of printed composites, the bonding strength between mortars and three types of steel cables with different diameters (0.5 mm, 1 mm, and 1.5 mm) was examined through pull-out tests. Moreover, four-point bending tests were conducted to examine the flexural performance of printed mortar beams reinforced with varying numbers and diameters of steel cables. Experimental results demonstrate that mortar filaments reinforced with 0.5 mm and 1 mm diameter steel cables can meet the buildability requirements within the designated open-time, while 1.5 mm diameter steel cables tend to rebound out of the fresh printed mortar due to their rebound force exceeding the grip strength of the mortar, rendering reinforced 3D printing unfeasible. Pull-out tests reveal that bonding strength between steel cables and 3D printed mortars is between 1.4 and 2.4 MPa. Due to steel cable's bundle structure and printing methods, this bonding strength is lower than that of traditional reinforced concrete. In addition, the flexural strength of printed beams reinforced with steel cables is increased by up to around 90%, and the ductile fracture mode trend was observed. This paper confirms the feasibility and effectiveness of this enhancement approach, providing a reference for other reinforcement methods in 3D printed building structures.