Investigation of interlayer adhesion of 3D printable cementitious material from the aspect of printing process

The safety of structure printed by extrusion-based 3D concrete printing (3DCP) is significantly influenced by interlayer bonding, which is governed by fresh material properties and processes, including mixing, printing, and post-processing phases. Much literature focused on improving interlayer bond strength via material tailoring/bonding agent addition but gave insufficient attention to other phases' impacts. This study investigates the effects of parameters on interlayer bond strength from different phases in 3DCP, including superplasticizer dosage, printing speed, and curing condition. In the mixing phase, the superplasticizer dosage was increased to reduce Ithix and increase surface moisture content (SMC), consequently improving interface microstructure and interlayer bond strength. In the printing phase, similar results were observed by increasing pumping speed to increase material shear rate. In the post-processing phase, proper curing also improved interlayer bond strength. While SMC has a critical impact on interlayer bond strength, material thixotropic index (Ithix) probably has a stronger influence.