High-temperature mechanical properties and microscopic analysis of nano-silica steel fibre RC

This paper investigated the high-temperature mechanical properties of nano-steel fibre-reinforced concrete (NSFC), steel fibre-reinforced concrete (SFRC) and normal concrete. The mechanical properties were compressive strength, splitting tensile strength and flexural strength. The microstructure and interfacial transition zone of steel fibre at different temperatures were also examined by scanning electron microscopy (SEM) and X-ray diffraction (XRD). The mechanical properties of NSFC are found to be better than those of SFRC and normal concrete at all test temperatures, particularly at 400°C, where the maximum values are reached. Compared with normal concrete, the compressive, splitting tensile and flexural strengths of NSFC increase by 27·0%, 63·3% and 54·1%, respectively, at room temperature, and by 35·1%, 84·6% and 87·2%, respectively at 400°C. SEM and XRD analysis show the existence of a permeable diffusion layer on the steel fibre surface because of the solid-state reaction in the interfacial transition zone of steel fibre and concrete. This layer is white, bright and serrated, and mainly consists of iron disilicide (FeSi₂) as well as the complex hydrated calcium silicate. The compounds of this layer change the interfacial transition zone structure, enhance the bonding capacity of the steel fibre and matrix, and also increase the high-temperature mechanical properties of concrete.