Multi-material printing to simultaneously enhance interlayer and flexural performance in 3D concrete printing

The layer-atop-layer construction process in 3D concrete printing (3DCP) has incurred two limitations: (1) the weak interlayer bond strength and (2) the difficulty of integrating steel reinforcement.Strain-hardening cementitious composites (SHCC) with high tensile properties have the potential to achieve self-reinforced structures in 3DCP.This study proposes a multi-material printing strategy by combining ductile (SHCC) and brittle (printable mortar) cementitious materials to address these two limitations simultaneously.SHCC are used as the bonding agents introduced at the interfaces of printed mortar.A dual-nozzle system is designed to achieve synchronized SHCC deposition and mortar printing.The splitting tensile test was adopted to evaluate the interlayer bond strength and four-point bending test was performed to study the flexural performance.The results show that the SHCC bonding agents can enhance the interlayer bond strength by 80% and reduce the interfacial porosity by 35%.In the SHCC-concrete beams, the flexural strength, deflection, and energy absorption capacity increase by 26%, 182%, and 800%, respectively, compared to the reference group without SHCC.The findings reveal that the proposed multi-material printing strategy has great potential to address the weak interlayer bond strength and reinforcement integration problems in 3DCP.