Bond behaviour of steel reinforcement in 3D printed alkali-activated concrete

3D concrete printing in construction enables efficient shape optimization and adaptation of structures to the internal flow of forces, at the same time permitting efficient material use without the need for formwork and heavy equipment. To meet the challenges of global warming, new, more environmentally-friendly materials, such as alkali-activated concretes, are becoming a sustainable alternative to Portland cement concrete. In this regard, a novel cement-free, ground granulated blast furnace slag (GGBFS)-based mixture for 3D printing was used in this study. Different continuous reinforcement types, such as ribbed rebar and barbed wire, were investigated in combination with this mixture, focusing on the bond behaviour of steel in 3D-printed alkali-activated concrete. Different rebar diameters and concrete layer orientations during the digital production of specimens were considered. Experimental investigation was carried out via pull-out tests, and results were compared to conventionally cast concrete. This study concludes that steel reinforcement can be efficiently used in combination with the novel alkali-activated GGBFS-based mixture in digital manufacturing. Results of pull-out testing confirmed orthotropic material behaviour resulting from layer-by-layer manufacturing, which influenced the bond strength of specimens with different concrete layer orientations. A correlation between the bond strength of steel reinforcement in 3DPC and the compressive strength of 3DPC was established. A modified bond strength formulation was proposed based on the findings of this study.