Effects of macro basalt fibers on the tensile behavior of ultra-high performance concrete

Macro basalt fibers (MBF), which is also named as basalt fiber reinforced polymer (BFRP) minibar, is a novel kind of fiber manufactured with BFRP. This work studied the effects of MBF on the tensile behavior of ultra-high performance concrete (UHPC) and proposed some MBF optimization recommendations based on the experimental results. Nine kinds of UHPC with MBFs and two kinds of UHPC with steel fibers or polypropylene (PP) fibers were designed for the tests of fiber distribution, density, compressive and tensile behavior. According to test results, UHPC with MBFs showed a more ideal fiber distribution compared to UHPC with steel fibers and PP fibers. For the samples with MBFs, UHPC with 3% twisted MBFs had the highest compressive strength, tensile strength and ultimate tensile strain, which were 138.9 MPa, 8.14 MPa and 1714 με, respectively. Compared to UHPC with steel fibers, UHPC with MBFs had slightly lower density and mechanical properties, but a similar stain-stress relationship. Thereby, the linear-exponential softening model was adopted to show the tensile stain-stress relationship of UHPC with MBFs. Based on the test results, three recommendations for optimizing MBF, which contained reducing fiber diameter for larger aspect ratio, optimizing fiber shape for higher fiber-UHPC bonding behavior and increasing the fiber modulus, were proposed to improve the mechanical properties of UHPC with MBFs.