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A series of uniaxial tensile tests on cylinders made from steel fibre reinforced selfcompacting concrete (SFR-SCC) have been carried out to investigate the influence of fibre geometry and the combined effect of fibre content and distribution on the post-cracking behaviour. Three types of commercially available hooked end fibres (3D (single hooked), 4D double (double hooked) and 5D (triple hooked)) have been used in this study, which are added to the concrete mixture at two fibre dosages (0.5 and 1% by volume). The experiments show that the post-cracking strength increases significantly (P˂ 0.05) with the increase of fibre content for all mixtures. The combination of a unique shaped hook of high tensile strength demonstrates an optimum effect on the failure mode of concrete cylinders in which peak and post-peak strengths are raised. Notably, strain-hardening behaviour is observed only for cylinders reinforced with 5D hooked end fibres. A correlation between number of fibres exposed on fractured surfaces and post-cracking behaviour is established.

This paper studies the effects of steel fibre geometry and architecture on the cracking behaviour of steel fibre reinforced concrete (SFRC), with the reinforcements being four types, namely 5DH (Dramix Ò hooked-end), 4DH, 3DH-60 and 3DH-35, of various hooked-end steel fibres at the fibre dosage of 40 and 80 kg/m 3 . The test results show that the addition of steel fibres have little effect on the workability and compressive strength of SFRC, but the ultimate tensile loads, post-cracking behaviour, residual strength and the fracture energy of SFRC are closely related to the shapes of fibres which all increased with increasing fibre content. Results also revealed that the residual tensile strength is significantly influenced by the anchorage strength rather than the number of the fibres counted on the fracture surface. The 5DH steel fibre reinforced concretes have behaved in a manner of multiple crackings and more ductile compared to 3DH and 4DH ones, and the end-hooks of 4DH and 5DH fibres partially deformed in steel fibre reinforced self-compacting concrete (SFR-SCC). In practice, 5DH fibres should be used for reinforcing high or ultra-high performance matrixes to fully utilize their high mechanical anchorage.

This paper represents an analytical model to predict the influence of the fibre geometry on the pull-out behaviour of various geometrical hooked end steel fibres. The model is established based on the concept of a frictional pulley along with two, three and four plastic hinges to simulate the mechanical anchorage effect provided by the hook. The mechanical contribution of the hook is a function of the cold work needed to straighten the fibre during the pull-out. The input parameters used in this model are directly related to geometrical and mechanical properties of each fibre. Model predictions are validated against experimental results for single fibre pull-out tests, and very good agreement is shown.

This paper presents the fibre-matrix interfacial properties of hooked end steel fibres embedded in ultra-high performance mortars with various water/binder (W/B) ratios. The principle objective was to improve bond behaviour in terms of bond strength by reducing the (W/B) ratio to a minimum. Results show that a decrease in W/B ratio has a significant effect on the bondslip behaviour of both types of 3D fibres, especially when the W/B ratio was reduced from 0.25 to 0.15. Furthermore, the optimization in maximizing pullout load and total pullout work is found to be more prominent for the 3D fibres with a larger diameter than for fibres with a smaller diameter. On the contrary, increasing the embedded length of the 3D fibres did not result in an improvement on the maximum pullout load, but increase in the total pullout work.Keywords: pullout behaviour, bond mechanisms, water/binder ratio, hook geometry, embedment length and fibre-matrix interface.

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This paper presents the effect of elevated temperature on the bond mechanisms associated with the pull-out behaviour of steel fibres. A series of pull-out tests have been performed on 4D and 5D hooked end steel fibres embedded in four different types of concrete, namely, normal strength concrete (NSC), medium strength concrete (MSC), high strength concrete (HSC) and ultra-high performance mortar (UHPM). At the age of 90 days, the specimens were heated to target temperatures of 100, 200, 300, 400, 500, 600, 700 and 800°C respectively. The influence of elevated temperature on the mechanical and thermal properties of concrete was investigated. The results showed that the pull-out response of both fibres does not vary significantly throughout 20-400°C temperature range, but within the temperature range of 600 to 800°C, the pull-out strength decreases significantly for all concretes. The comparisons between the two fibre types show that the mechanical anchorage contribution provided by the 5DH fibre is significantly higher than that of the 4DH fibre, especially for higher strength concretes. The reduction in bond strength of both fibres after elevated temperature exposure is found to correlate closely with the degradation in compressive strength of the concretes.