Effect of elevated temperature on pull-out behaviour of 4DH/5DH hooked end steel fibres

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 600-800 °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.