Influence of Steel Fiber Content on Mechanical Properties of Ultra-High Performance Concrete

In order to analyze the effects of steel fiber volume content on the mechanical properties of Ultra-High Performance Concrete（ UHPC）,three groups of steel fiber UHPC specimens with volume content of 1. 0%,1. 5% and2. 0% were designed and prepared. Slump,expansion,compressive strength and four-point bending tests were carried out. The results show that with the volume content of steel fiber from 0% to 2%,the slump decreases from 265 mm to240 mm,the expansion decreases from 540 mm to 425 mm,and the compressive strength increases from 103. 9 MPa to123. 7 MPa. When the steel fiber content is 1. 0%,1. 5% and 2. 0%,respectively,the flexural strength is 16. 7MPa,23. 1 MPa and 23. 8 MPa,and the bending toughness is 87. 6 N·m,116. 0 N·m and 122. 8 N·m,respectively. With the increase of steel fiber content,the fluidity of UHPC decreases. The compressive strength,flexural strength and flexural toughness of UHPC showed an increasing trend,but the increasing trend slowed down. Because steel fiber mainly bears tensile stress and bridging matrix,the indexes of flexural strength and flexural toughness increase more in the indexes of compressive strength,flexural strength and flexural toughness.