Bond properties of reinforcing bar penetrations in 3D concrete printing

Extrusion based 3D concrete printing is an emerging construction automation technology. A major challenge is an automated 'in-process' reinforcing method while the 3D printing. This study presents an effective in-process reinforcing technique by penetrating deformed reinforcing bars through a predefined number of freshly printed layers. The bond varies along the penetration depth due to differing levels of disturbances experienced by the layers due to the penetrated bar. To characterise the bond at different depths, pull out tests are performed on sections of a 350 mm bar penetrated through a printed wall. The results are then compared to a separate sample on a sand bed with varying lengths of bar penetrated through. The sand bed method was used to isolate the effect of damage due to penetration action. It was found that penetrations over 90 mm caused significant damage. The bond mechanism is investigated and explained with supportive evidences.