Steel fiber orientational distribution and effects on 3D printed concrete with coarse aggregate

In this study, the first insight into the extrusion-based 3D printed steel fiber reinforced concrete with 5-20 mm coarse aggregate (3DPSFRC) is presented. The fresh properties and mechanical performance of 0%, 1% and 2% fiber content 3DPSFRC were investigated and compared with those of the cast. Through the deep-learning segmentation method, the centerlines of steel fibers in the X-ray micro-computed tomography image sequence are extracted and 3D analyzed. The orientational distribution coefficients were introduced to quantitatively indicate the degree of steel fiber inclination in the printing (theta) and stacking directions (gamma) inside the 3DPSFRC. Results indicate that the flowability of 3DPSFRC was decreased due to the presence of steel fibers compared with plain concrete. The enhancement effect of steel fiber on the compressive, flexural, and axial tensile strength (up to 73.24 MPa, 8.71 MPa, and 7.58 MPa, respectively) and post-peak toughness of 3DPSFRC is remarkable. The weakening of orientational distribution coefficients and the partial divergence distribution of steel fibers are related to the presence of coarse aggregate. Further, the anisotropy of 3DPSFRC in the compressive and flexural tests is weakened owing to the changes in the fiber orientational distribution after the steel fiber content increases.