Pull-out behavior of straight steel fibers from asphalt binder

The interaction between a straight steel fiber and the surrounding asphalt matrix is investigated through single fiber pull-out tests and numerical simulations. Based on experimental observations from 240 pull-out tests for various temperatures, displacement rates, and fiber dimensions, pull-out failure modes are classified into three types: matrix, interface, and mixed failure modes. The experimental data suggests that there is a critical shear stress beyond which fiber-binder interface debonding will occur. Detailed finite element analyses employing a nonlinear viscoelastic constitutive model for asphalt are carried out to explain the observed test results. The numerical simulations show that the stress distribution along the fiber surface varies substantially with temperature and fiber dimensions. At −20 °C, the concentration of interfacial shear stress becomes significant as the embedded aspect ratio of fibers becomes higher, and causes a decrease in the value of average interfacial shear stress at the onset of the interface debonding. The simulations also showed that this stress concentration decreases at 0 °C as the contribution of viscous behavior becomes more significant. The simulation results confirm that the shear bond strength between steel fiber and asphalt binder is 6.9 MPa, and it is independent of temperature, loading rate, and fiber dimensions within the ranges used in the study.