Development of CO₂-activated interface enhancer to improve the interlayer properties of 3D-printed concrete

This paper presents an approach to enhance the interlayer properties of 3D-printed concrete (3DPC) by synchronously spraying CO₂-activated interface enhancer (CIE) onto the surface of printed concrete filament during the printing process, thus overcoming the inherent limitation of weak interlayer properties and unlocking new possibilities for automation construction. The CIE was developed by using dicalcium silicate (C₂S), a binder mineral with high carbonation activity. It was found that applying a 100 μm thick CIE resulted in a remarkable enhancement ratio of 249.3 % in the interlayer strength of 3DPC at 28 days. Subjected carbonation, CIE produced calcium carbonates and silica gel, which effectively filled the interlayer microstructure, leading to a reduced porosity. Furthermore, the activation of the CIE led to the growth of spear-like calcium carbonate crystals and rod-like ettringite crystals, which played a crucial role in enhancing the bonding performance by forming an interlocking microstructure. Contrary to common belief, a prolonged printing interval was beneficial for CIE, as it allowed for increased CO₂ penetration, thereby enhancing the carbonation degree. In conclusion, the CIE developed in this study can be considered a promising approach for enhancing the interlayer properties of 3DPC.