Pull-out behaviour of straight and hooked-end steel fibres under elevated temperatures

This paper presents the results of an experimental investigation into the effect of elevated temperature on the steel fibre-matrix bond characteristics. A series of pull-out tests on straight and hooked-end fibres embedded in four different cementitious matrixes, namely normal strength concrete (NSC), medium strength concrete (MSC), high strength concrete (HSC) and ultra-high performance mortar (UHPM) were performed. Ninety days after casting, the specimens were heated to target temperatures of 100, 200, 300, 400, 500, 600, 700 and 800 °C, respectively. The initial and residual thermal and mechanical properties of the concrete were investigated. It was shown that while the variation in compressive strength and pull-out response for different temperatures is relatively small up to 400 °C, further increase in temperature results in a reduction in the pull-out strength, especially for the temperature > 600 °C. At 800 °C, the maximum pull-out load of the hooked-end fibres with NSC, MSC and HSC decreased by 54%, 64% and 56%, respectively.The first author gratefully acknowledges the financial support of the Ministry of Higher Education and Scientific Research of Iraqi Government for this Ph.D. project