Pull-out behaviour of hooked-end steel fibres in cracked concrete exposed to wet-dry cycles of chlorides and carbon dioxide – mechanical performance

This paper presents an experimental study investigating the pull-out behaviour of hooked-end carbon-steel fibres exposed to wet-dry cycles of freshwater and saltwater for six months. Experimental results from single-fibre pull-out tests of partially pulled fibres in a simulated crack were used to quantify the impact of corrosion damage at the fibre and alteration of fibre-matrix interface on the fibre-matrix bond strength after the exposure.

The results presented in this paper show that the maximum pull-out force and total work transferred by the fibres during pull-out increased both with increasing steel strength and matrix strength. Exposure of partially pulled steel fibres also resulted in an increase of the fibre-matrix bond strength over time. Thus, generally leading to higher maximum pull-out forces and moderate increase in toughness after exposure, provided that fibre rupture did not occur. Fibre rupture during pull-out occurred due to both the increase of the fibre-matrix bond strength after exposure and the reduction of the effective cross-section of the fibre as a result of corrosion. Overall, increasing the steel strength and reducing the bond-strength of the fibre was effective in reducing substantially the amount of fibres rupturing during pull-out.

This investigation substantiates ongoing discussion that proposes additional damage mechanisms, besides fibre corrosion, that explain the changes in the residual performance of the cracked Steel Fibre Reinforced Concrete (SFRC) exposed to wet-dry cycles of freshwater and saltwater.