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This paper presents an experimental investigation into the mechanisms altering the pull-out behaviour of partially pulled hooked-end steel fibres inside an artificial crack exposed to wet–dry cycles of chlorides and carbon dioxide for 6 months. Mechanical and corrosion damage at the surface of the steel fibre was investigated using three-dimensional optical interferometric profiling, and petrographic analyses were used to describe damage and healing processes at the matrix surrounding the fibre. Mechanical damage observed in the cementitious matrix and at the fibre's surface confirmed that the pull-out process was governed by yielding of the fibre, fracture of the adjacent matrix, and friction between the hook and the matrix. Increases in the pull-out force of partially pulled-out fibres after exposure were connected to accumulation of corrosion products from the steel fibre and to alteration of the cement matrix surrounding the fibre. This study concluded that autogenous healing and carbonation of the damaged cement matrix around the fibre are the main mechanisms responsible for the increase in the fibre–matrix bond strength of hooked-end steel fibres bridging cracks in concrete exposed to wet–dry cycles. [ABSTRACT FROM AUTHOR]

This paper presents an experimental study investigating the corrosion damage of carbon-steel fibre reinforced concrete (SFRC) exposed to wet–dry cycles of chlorides and carbon dioxide for two years, and its effects on the mechanical performance of the composite over time. The results presented showed a moderate corrosion damage at fibres crossing cracks, within an approximate depth of up to 40 mm inside the crack after two-years of exposure, for the most aggressive exposure conditions investigated. Corrosion damage did not entail a significant detriment to the mechanical performance of the cracked SFRC over the time-scales investigated. Corrosion damage to steel fibres embedded in uncracked concrete was negligible, and only caused formation of rust marks at the concrete surface. Overall, the impact of fibre damage to the toughness variation of the cracked composite over the time-scale investigated was secondary compared to the toughness variation due to the fibre distribution. The impact of fibre corrosion to the performance of the cracked composite was subject to a size-effect and may only be significant for small cross-sections. [ABSTRACT FROM AUTHOR]

• Fibre bundle models can describe variations in the toughness of cracked SFRC. • The tensile strength of SFRC increased due to an increase of fibre bond strength. • Corrosion damage of steel fibres is not the only deterioration mechanism of SFRC. • Excessive increase of the fibre bond strength result in toughness loss of SFRC. This paper investigates variations in the tensile toughness of cracked steel fibre reinforced concrete (SFRC) subjected to corrosion damage, by means of a multiscale modelling framework. Experimental results were used to discretise the pull-out behaviour of single fibres using a spring-slider model, which were then upscaled to the composite level by means of a probabilistic fibre bundle approach. The model described the alteration of the residual tensile performance of the composite due to variations of the fibre-matrix bond strength and corrosion damage of the steel fibres, observed experimentally. This investigation supports recent hypotheses suggesting that corrosion damage of the steel fibres may not be the only mechanism responsible for the deterioration reported in cracked SFRC exposed to corrosive environments. The strengthening of the fibre-matrix bond over time may entail a decrease of the tensile toughness of the composite due to fibre rupture. [ABSTRACT FROM AUTHOR]

• Exposure to wet-dry cycles increased the fibre-matrix bond strength of steel fibres. • The bond of partially pulled fibres was restored after exposure to wet-dry cycles. • Corrosion damage mainly occurred at the steel exposed to the artificial crack. • Fibre rupture occurred due to corrosion damage and increase in the bond strength. 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. [ABSTRACT FROM AUTHOR]