A multi-index synthetical evaluation of pull-out behaviors of hooked-end steel fiber embedded in mortars

Focusing on the fundamental issue of the bond performance of steel fiber in cementitious matrix of concrete, a multi-index synthetical evaluation was carried out to link the bond mechanisms to the features of complete load-slip curve of hooked-end steel fiber under a pull-out test. The features of curve at ascending portion, peak and descending portion of hooked-end steel fiber embedded in mortar were quantitatively characterized by the indexes of strength and energy dissipation capacity. Eight groups of specimens were experimentally investigated with the factors including the mortar strength ranged from 25 MPa to 90 MPa, the river sand and manufactured sand, and the embedded length of fiber varied from 6 mm to 14 mm. Except the bond strength used conventionally, the debonding strength and the residual bond strength are extracted to represent the strengthening effect, while the pull-out work and the debonding energy ratio, slipping energy ratio and pull-out energy ratio are extracted to represent the toughening effect of steel fiber on matrix of concrete. Meanwhile, the strength use efficiency of steel fiber is introduced to estimate if the fracture of steel fiber happens and to determine a rational tensile strength of steel fiber matched with concrete. Results indicated that the higher mortar strength and manufactured sand benefit to the bond performance of hooked-end steel fiber, and the hooked-end steel fiber used in this test with tensile strength of 1150 MPa matches better with mortars of 65 ~ 90 MPa compressive strength. The hooked-end plays a controlling role providing reliable bond performance of steel fiber, the rational length of hooked-end steel fiber can be optimized in view of the bond requirement. This gives a useful method to quantitatively evaluate the validity and adaptability of steel fiber used for concrete.