Daniel Game

Automated and seamless integration of reinforcement is one of the main unresolved challenges in large-scale additive construction. This study leverages a dual-reinforcement solution consisting of high-dosage steel fiber (up to 2.5% by volume) and short vertical reinforcements as a complementary reinforcement technique for 3D-printed elements. The mechanical performance of the printing material was characterized by measuring the compressive, flexural, and uniaxial tensile strengths of mold-cast specimens. Furthermore, the flexural performance of the plain and fiber-reinforced 3D-printed beams was evaluated in the three main loading directions (X, Y, and Z-directions in-plane). In addition, short vertical threaded reinforcements were inserted into the fiber-reinforced 3D-printed beams tested in the Z-direction. The experimental results revealed the superior flexural performance of the fiber-reinforced beams loaded in the longitudinal directions (X and Y). Moreover, the threaded reinforcement significantly increases the flexural strength and ductility of beams loaded along the interface, compared to the control. Overall, the proposed dual-reinforcement approach, which exhibited notably less porosity compared to the mold-cast counterpart, holds great potential as a reinforcement solution for 3D-printed structures without the need for manual operations.

The objective of this study was to evaluate the feasibility of developing practical and cost-effective ultra-high-performance engineered cementitious composites (UHP-ECCs) using natural river sand and no silica fume (SF). Fresh and hardened properties of composites utilizing river sand, with and without SF, and incorporating 1.5 and 2 vol% (volume percent) ultra-high-molecular-weight polyethylene fibers were evaluated. Furthermore, matrix and fiber/matrix interface properties were investigated. Experimental results showed that the inclusion of SF generally produced negative impacts in the mechanical strength (i.e., compressive, tensile, and flexural) and ductility of the composites, which was mainly attributed to a worsening fiber dispersion. This was supported by the loss in workability observed when increasing fiber content or implementing SF. Clear tendencies in the effect of fiber content on the mechanical strength of the composites were not observed. However, increment in fiber content decreased the tensile ductility of the materials, presumably because of poor fiber dispersion. All the mixtures evaluated exhibited pseudo strain-hardening (PSH) behavior and ECC-like ductility, which was supported by the PSH strength and energy indexes obtained, which exceeded the minimum recommended values for robust PSH behavior. Practical and cost-effective UHP-ECC materials (i.e., cementitious composites simultaneously exhibiting compressive strength >120 MPa and tensile strain capacity >2%) using natural river sand and no SF were successfully developed, which to the authors’ knowledge was achieved for the first time.