Pull-out behaviour of single and multiple hooked-end steel fibres embedded in alkali-activated slag-based concrete and Portland cement concrete: Experimental and numerical investigation

This paper investigates the 7-day and 28-day pull-out behaviour of single (3D), double (4D), and triple hooked-end steel fibres (5D) embedded in alkali-activated slag-based concrete (AASC) and Portland cement-based concrete (PCC). Experimental results indicate that both the maximum pull-out load and the average fibre-matrix bond strength increase with the number of bends at the fibre ends, with AASC consistently outperforming PCC, confirming a stronger fibre-matrix interfacial bond strength in the alkali-activated system. An inverse analysis was performed to identify the interface Cohesive Zone Model (CZM) parameters implemented in ABAQUS using data obtained from the experimental single-fibre pull-out tests. The parameters governing the initial slope and the maximum pull-out load (interface stiffness and traction stress, respectively), as well as those controlling the post-peak behaviour (separation and friction coefficients), were identified. The results show that the interface stiffness parameter increases with the number of bends at the fibre ends, and the fibre-matrix bond fracture energy, derived from the traction stress and separation, was highest for double hooked-end (4D) fibres, which also exhibited the highest fibre material utilisation factor. ... mehrFinally, by combining the average fibre-matrix bond strength with the number of fibres in the cross-section of notched beams tested under three-point bending, a linear relationship was established between single-fibre pull-out behaviour and residual flexural strengths at serviceability and ultimate limit states.