A bond model of synthetic macro-fibre in concrete

Abstract

Bond behaviour of a synthetic macro-fibre in concrete is the object of this research. The bond strength and stiffness are the parameters characterising the bonding mechanism that determines the efficiency of the reinforcing material. However, there is no general methodology developed to evaluate these properties. There also exists neither a straightforward procedure to estimate the bond quality of a synthetic macro-fibre nor a reliable numerical model to mimic the bond behaviour of such fibres. In this work, the bond mechanisms of 40 mm long synthetic macro-fibres are investigated using pull-out tests: 32 concrete cubes were made for that purpose. Two types of synthetic macro-fibres available at the market are investigated. In each test sample, three fibres were placed perpendicular to the top surface and two sides; two bonding lengths (10 mm and 20 mm) were considered. A gripping system was developed to protect the fibres from local damage. The obtained load-displacement diagrams demonstrated that mechanical parameters of the bond (strength and deformation modulus) of the “top” fibres are almost 20% weaker than that of the fibres positioned to the side surfaces. Therefore, the results of the “top” fibres were excluded from further analysis. One fibre type was chosen for numerical modelling because of sufficient strength of the fibre material to activate the bond-slip mechanism. A physically non-linear finite element model of the pull-out sample was developed. A bond model was proposed to simulate deformation behaviour of the fibre with the different bonding length.