A new orientational molding method for ultra-high performance concrete with high content of steel fiber and investigation on its flexure and axial tensile properties

Abstract

Although ultra-high performance concrete (UHPC) has ultra-high mechanical properties (compressive strength up to 150 MPa), the tensile strength to compressive strength ratio is even lower than that of ordinary concrete (less than0.1). Therefore, improving the flexural and tensile properties of UHPC is an important issue in civil engineering. In this paper, based on the vibration and cement paste flow control, a fiber orientational extrusion nozzle was designed. Then, a new orientational molding method for UHPC was developed. Four groups of UHPC with different steel fiber contents were designed (0 vol%, 2 vol%, 4 vol%, and 6 vol%) and fabricated by the new method. The flexural and axial tensile performance of UHPC were systematically studied. The results indicated that the new orientational molding method was suitable for manufacturing UHPC with high content of steel fibers, which reached even 6 vol%. With the orientational molding method, the flexural strength and axial tensile strength of UHPC with 4 vol% content of steel fiber reach 55.6 MPa and 14.1 MPa, respectively. In addition, the results show that the flexural and tensile strengths of the specimens formed using the oriented technique were maximum at 4 vol%. The flexural strength increases with increasing fiber content as the fiber content increases from 0 vol% to 4 vol%. However, the flexural strength decreases at 6 vol% fiber content. Besides, X-ray micro-computed tomography (CT) was used for the analysis of the orientation of steel fiber. Results indicate that most of the fibers showed parallel to the casting path orientation when using the orientational molding technique. The orientational rates were 72%, 81%, and 75% for fiber contents of 2 vol%, 4 vol%, and 6 vol%, respectively.