Corrosion risk of steel fibre in concrete

• The corrosion risk of steel fibre in mortar is lowered by millscale on the surface.
• Chloride transport was increased by porosity at the interface of steel fibre.
• Pores were formed in the vicinity of steel fibre by trapping air bubbles in casting.

In the present study, the corrosion risk of steel fibre in concrete was assessed by measuring the corrosion rate of steel fibre in chloride-contaminated mortar. Simultaneously, the rate of chloride transport in steel fibre mortar was determined by chloride profiles. Then, the interface of the steel fibre was examined by the scanning electron microscopy to ensure the porosity in the vicinity. As a result, it was found that the corrosion resistance of steel fibre against chloride was slightly higher than for reinforcing steel rebar in concrete, presumably due to the presence of mille scale on the surface; the chloride threshold level ranged 0.8–1.0% by weight of cement. However, transport of chloride ions in concrete containing steel fibre was accelerated by increased porosities in the vicinity of steel fibre, implying that external aggressive ions may easily penetrate the concrete then to chemically degrade concrete properties. In fact, the diffusion coefficient of chloride in mortar containing steel fibre ranged 4.79–9.61 × 10−12 m2/s, as being 2–3 times higher for steel fibre-free mortar.