Large scale 3D printed concrete wall: Interlayer bonding and shrinkage

In 3D concrete printing technology, the absence of formwork exposes freshly extruded concrete to ambient temperature and humidity, which facilitates the occurrence of shrinkage. Shrinkage adversely affects the stability and geometric accuracy of printed elements, particularly in large-scale structures, and consequently influences their performance and durability. This study investigates the relationship between shrinkage and interlayer bond strength in 3D printed concrete (3DPC) walls. Three full-scale 3DPC walls, each 3 m in length and 2 m in height, were fabricated using a giant 3D printer with different concrete mixtures. Water-to-binder (W/B) ratios of 0.30, 0.34, and 0.40 were adopted, corresponding to superplasticizer contents of 0.22 %, 0.16 %, and 0.10 % by cement weight, respectively, while the polypropylene fiber content was maintained at 0.79 kg/m³ . The mixtures consisted of ordinary Portland cement (OPC), limestone powder (LP), river sand (S), water (W), superplasticizer (SP), and polypropylene (PP) fibers. Shrinkage development was continuously monitored using embedded strain gauges, and interlayer bond strength at 28 days was evaluated through splitting tensile tests. The results indicate that interlayer bond strength is strongly dependent on printing position, layer height, and shrinkage behavior. Increasing the W/B ratio led to greater shrinkage and a corresponding reduction in interlayer bonding. Specifically, the wall with a W/B ratio of 0.40 exhibited a 24 % higher maximum shrinkage strain and an approximately 29 % lower interlayer bond strength compared to the wall with a W/B ratio of 0.30. Moreover, on a specific 3D printed concrete wall, bottom layers have higher bond strengths than those of upper concrete layers due to its lower shrinkage. Finally, there was an inversely proportional relationship between the shrinkage and interlayer bonding strength of the 3D printed concrete wall.