A comprehensive review on 3D concrete printing: extruder design, material properties and reinforcement techniques

Purpose This review systematically examines advancements in extrusion systems, reinforcement integration and material optimization for 3D concrete printing (3DCP), addressing critical challenges such as printability, structural integrity and scalability. It aims to synthesize innovations in extruder design, evaluate reinforcement strategies and assess material modifications. This study aims to identify persistent technical barriers and proposes future research directions to advance 3DCP as a viable solution for large-scale, sustainable construction. Design/methodology/approach A structured review methodology was used, beginning with a comprehensive database search and then eligibility screening and analysis of peer-reviewed articles. The review focuses on three domains – extruder mechanisms, reinforcement techniques and material systems. Findings In 3DCP, extruder advancements enhance performance through progressive cavity pumps with variable clearance and dual-pitch screws, optimizing material flow and pressure. Screw extruders with excitatory blades counter thixotropic behavior, while conical designs minimize air entrapment. Tapered hoppers ensure consistent mass flow, reducing phase separation and dead zones for stable non-Newtonian concrete extrusion. Reinforcement strategies include short fibers for improved ductility, continuous steel cables for significantly enhanced flexural strength and U-nail insertion for stronger interlayer bonding. Material innovations involve chemically modified mortars for better setting time and an inline mixing system that enables rapid material stiffening for large-scale or vertical construction. Some challenges include rheological instability, reinforcement-material incompatibility, scalability limitations and energy-intensive dynamic mixing. Originality/value The critical analysis of the extruder for the 3DCP system and mechanisms described in this review paper is the originality of this article.