A Modular Approach for Steel Reinforcing of 3D Printed Concrete (2020-05)¶

3D concrete printing technology has considerably progressed in terms of material proportioning and properties; however, it still suffers from the difficulty of incorporating steel reinforcement for structural applications. This paper aims at developing a modular approach capable of manufacturing 3D printed beam and column members reinforced with conventional steel bars. The cubic-shaped printed modules had 240 mm sides, possessing four holes on the corners for subsequent insertion of flexural steel and grouting operations. The transverse steel (i.e., stirrups) was manually incorporated during the printing process. The reinforced 3D printed beams were built by joining the various modules using high-strength epoxy resins. Test results showed that the compressive and flexural strengths of plain (i.e., unreinforced) 3D printed specimens are higher than traditionally cast-in-place (CIP) ones, which was mostly attributed to the injected high-strength grout that densifies the matrix and hinders the ease of crack propagation during loading. The flexural moment capacity of 3D reinforced printed beams were fairly close to the ACI 318-19 code provisions; however, about 22% lower than companion CIP members. The reduction in peak loads was attributed to the modular approach used to construct the 3D members, which might alter the fundamentals and concepts of reinforced concrete design, including the transfer and redistribution of stresses at ultimate loading conditions.