Quantitative Evaluation of Orientation of Steel Fibers in 3D-Printed Ultra-High Performance Concrete

摘要

Despite the growing interest in 3D concrete printing,the inset of tensile reinforcement poses severe limitation to the advancement of the technology.Inclusion of short steel fibers is a potential alternative to improve the tensile properties of 3D-printed concrete.In the extrusion-based printing process,steel fibers tend to align predominantly in the printing direction.However,currently there is no quantitative evaluation of the orientation of fibers in 3D-printed fiber-reinforced concrete.An experimental program was designed in this study to quantitatively investigate the fiber alignment in a non-proprietary 3D-printable ultra-high performance fiber-reinforced concrete(UHPFRC).Digital image analysis was performed on thin UHPFRC specimens to quantify the fiber orientation distribution.In addition,the effect of the fiber orientation on the mechanical response of the 3D-printed UHPFRC with 2% by volume of micro steel fibers was determined by means of three-point bending tests.Conventionally mold-cast UHPFRC specimens were also prepared and tested for comparison purposes.The results of the digital image analysis revealed an enhanced fiber alignment parallel to the printing direction in the 3D-printed specimens,which in turn significantly enhanced the flexural performance of the printed UHPFRC as compared to the mold-cast counterpart.