Effects of silane treatment on the bond between steel fibres and mortar

Abstract

The ability of fibres to resist crack growth in fibre-reinforced concrete (FRC) can be significantly influenced by the fibre/matrix bond. This investigation reveals surface treatment of fibres as a viable technique to develop a uniform bond along the fibre/cement interface to resist growth of microcracks and thereby complement the physical restraint against pull-out provided by fibres’ shape and friction. Previous reports have shown effective chemical treatment of glass, carbon, and polypropylene fibres. However, research into chemical surface treatment processes for steel fibres, the most common in concrete, is scarce and focused on corrosion and dispersion, rather than the fibre/matrix bond. Here, a silane treatment technique is proposed to strengthen the steel fibre/cementitious matrix bond. Surface energy measurements and XPS demonstrate the effectiveness of this treatment. Fibre pull-out tests conducted on silane-treated fibres show an apparent increase in pull-out energy, accompanied by a delay in reaching the peak load, compared to untreated fibres, suggesting increased resistance to crack initiation and growth. Furthermore, the results indicate improved flexural strength and direct tensile strength of mortar reinforced with silane-treated fibres compared to untreated fibres. The improvements are further corroborated by results from restrained drying shrinkage and volume of permeable voids.