Tensile Creep of Cracked Steel Fibre Reinforced Concrete: Mechanisms on the Single Fibre and at the Macro Level

Abstract

This paper reports on tests done to investigate the mechanisms causing the increased tensile creep of cracked fibre reinforced concrete (FRC) members when a sustained load is applied. It is important to understand the mechanisms as this will pave the way for improvements that can be made to reduce this creep and will also assist in creating prediction models as it will be based on the fundamental mechanisms involved. This paper presents results of uni-axial tensile creep tests of cracked steel fibre reinforced concrete (SFRC) and also tests at the single fibre level. Single fibres were embedded in the matrix and pull-out at different rates and sustained loading was also applied to the single, embedded fibres. It was found that the single fibre pull-out creep test results can be directly linked to the uni-axial tensile tests. It was also shown that the pull-out creep is proportional to the load up to at least 50 % of the ultimate load after which the pull-out creep increases non-linearly. This can be ascribed to micro-cracking around the hooked-end of the fibre. Lastly, it is postulated that the interfacial transition zone between the fibre hooked-end and the concrete matrix plays a significant role in the pull-out creep behaviour.