Pull-out behaviour of spiral-shaped steel fibres from normal-strength concrete matrix

Reinforcing concrete with steel fibres has been proven being able to improve the properties of concrete such as strain capacity, impact resistance, energy absorption and tensile strength because the discrete steel fibres act as dispersed reinforcement in mitigating crack propagation. A number of laboratory tests in recent years have indicated the superiority of spiral geometry of steel fibres as compared to other fibre types in terms of ductility, crack controllability, dynamic strengths and energy absorption. Understanding fibres' pull-out behaviour is essential to evaluate the properties of steel fibre reinforced concrete (SFRC). The pull-out behaviour of straight, hooked-end and twisted steel fibres have been investigated by many researchers. However, there has been no study that focuses on pull-out behaviour of spiral fibres in the literature yet. The pull-out behaviour of steel fibre with spiral geometry from concrete matrix is experimentally investigated in the present study. In addition, steel fibres with hooked ends were also prepared and tested for comparison. The spiral fibres with various geometric characteristics such as pitch length, embedment length and coil diameter were pulled out from concrete matrix at different rates. Test results showed several peak loads before reaching a final maximum pull-out force. Based on the experimental results, the influences of embedment length, pull-out rate, coil diameter and pitch length were investigated. Through analysing the testing results, combining hooked-end fibres and spiral fibres was proposed as a hybrid steel fibre reinforcement technique in order to further improve the performance of SFRC materials and structures. Laboratory tests in this study proved the effectiveness of this technique in enhancing the capacity of the reinforced concrete structure. (C) 2017 Elsevier Ltd. All rights reserved.