Time-dependent pull-out behaviour of hooked-end steel fibres in concrete

The popularity of Fibre Reinforced Concrete (FRC) is increasing in the industry due to its property to resist crack initiation, to control crack widening and improve the mechanical properties of concrete. Numerous studies have been done on the mechanical behaviour of FRC subjected to short term loading conditions. Although studies have been performed on the long term loading behaviour, little information is still known about it, especially in the cracked state. Even though the fibres resist crack widening, it has been revealed that the crack opens significantly under sustained loading. This unknown behaviour is associated with time-dependent fibre pull-out. In this study the pull-out behaviour of single hooked-end steel fibres embedded in concrete was investigated under both sustained loading and pull-out under different loading rates. Four pull-out loading rates were considered ranging from 2.5 mm/s to 0.00025 mm/s. The sustained load tests were performed over a period of 249 days and the sustained load was varied from 30% to 85% of the maximum (short term) interfacial shear resistance. Finally, a model is proposed that is able to simulate both the long term and short term time-dependent single fibre pull-out behaviour.