Shotcrete based 3D concrete printing: State of art, challenges, and opportunities

Shotcrete-based 3D printing (SC3DP) has been developed as an alternative concrete additive manufacturing process to the more widely used extrusion-based printing in order to overcome the challenges that extrusion-based 3D concrete printing technique faces, such as weak interlayer bond and difficulties in building overhangs and vertical elements. In SC3DP, printing layers are formed by a shotcreting process instead of extrusion. With the assistance of substrate, formwork, or reinforcement meshes, vertical and overhanging elements can be easily built using SC3DP. Free-formed SC3DP has also been realized by the researchers via a printing path that is similar to traditional extrusion-based printing with enhanced interlayer bond. This paper is a comprehensive review of the past works on SC3DP. The paper reviewed the SC3DP process and the material and operational parameters that affect this process, the mechanical performance of SC3DP, and ways to incorporate reinforcement. The paper also highlighted the potential challenges or knowledge gaps that need to be addressed to further advance the SC3DP technology and future research opportunities based on previous works and existing challenges.