In-situ coating technique for rebar installation for 3D-printed reinforced concrete

Directly-installed rebars have weak adhesion with the surrounding concrete during the 3D printing process, which compromises the mechanical properties and durability of the final outputs. This study presents an in-situ coating technique to coat the rebars inserted in a composite with high-fluidity reinforcing materials (epoxy resin), which contributes to macro, meso, and micro enhancements and increases the buildability of the printable mortar with the release of heat. Microscopic characterizations elucidated the mechanisms of loose bonding and in-situ coating enhancement. Pull-out tests revealed that the grouted epoxy enhanced the bonding strength by up to 418.2%. The in-situ formed mechanical anchorages contributed to a further improvement of 337.0%, achieving an overall improvement of 755.2%. With the original weak layer adhesion limit, this in-situ coating technique increased the flexural strengths of the cast and printed rebar-reinforced beams by 39.7% and 13.0%, respectively. The hybrid manufacturing system of printing and in-situ coating is technically feasible for effectively promoting the mechanical properties and durability of 3D-printed concrete structures.