Title: Dual-Reinforcement Approach for Printable Cementitious Mixtures: Studying the Structural Properties of Printed Elements

Presented By: Ilerioluwa Giwa, Louisiana State University

Description: Seamlessly integrating reinforcement during the automated layering process without compromising the structural integrity of the structure has remained one of the major challenges in the field of construction 3D printing (C3DP). In this study, we propose high-dosage steel fiber inclusion together with threaded vertical reinforcement as a dual C3DP reinforcement strategy with a potential for full automation. Initially, we formulated and tested several printing mixtures by characterizing the fresh-state and hardened properties, considering different sand-powder ratios, cement replacement levels with limestone powder, and fiber dosages (up to 2.5 % vol.). Upon successful development and characterization of steel fiber-reinforced mixtures with more than a 129% increase in tensile and flexural strength, the highest-performing printing material was further enhanced with threaded reinforcement inserted vertically into the freshly printed beams (100 x 100 x 350 mm). By testing the beams under the three main loading directions, the four-point bending test results revealed significant strength and ductility improvements in the longitudinal directions (parallel to the printing direction – X and Y), while no significant improvement was observed in the Z direction. Furthermore, although the flexural strength of samples with the threaded reinforcement did not increase significantly, there was a substantial improvement in the ductility. Overall, it seems the proposed dual reinforcement technique holds great potential for automated reinforcement of 3D printed structures. Future research on the required development and lapping length for different types of vertical C3DP reinforcement is needed to increase the efficiency of vertical discontinuous reinforcement.

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