Effect of nanosilica and silica fume content on the bond properties of macro-synthetic fibre in cement-based composites

In this study, the effects of nanosilica and silica fume content on the bond properties of macro-synthetic fibre in cement-based composites were investigated. The pullout behaviour of macro-synthetic fibre was evaluated by performing dog-bone bond tests according to JCI SF-8 at nanosilica and silica fume replacement ratios of 0, 2, 4, 6 and 8% based on cement weight. The addition of nanosilica and silica fume had a significant effect on the bond properties of macro-synthetic fibre. Specifically, the addition of 0∼2% nanosilica enhanced pullout behaviour, bond strength and interface toughness, whereas 4% or more nanosilica reduced pullout behaviour, bond strength and interface toughness. For silica fume, pullout load-to-displacement behaviour, bond strength and interface toughness increased in the range of 0 to 8%. These results demonstrate that the presence of nanosilica and silica fume strengthen the fibre–matrix interface of macro-synthetic fibre in cement-based composites by filling voids in the interface region. The relative bond strength and interface toughness were also analysed, except for compressive strength, to evaluate the bond properties of macro-synthetic fibre in cement-based composites at various nanosilica and silica fume replacement ratios. The ratios of nanosilica and silica fume had a significant effect on bond properties, regardless of the compressive strength of the cement-based composites. Microstructural analysis of macro-synthetic fibre after pullout tests showed scratches due to friction.