Development of self-sensing cementitious composites incorporating CNF and hybrid CNF/CF

Self-sensing cementitious composites have gathered particular interest as they can fulfil the structural health monitoring demand in order to evaluate the condition of the structures and predict the service life of structures. Carbon fibre (CF) has been proved to be the most effective additive in enhancing the electrical conductivity and piezoresistive properties of cementitious composites. However, with the development of nanotechnology, carbon nanomaterials have found not only effective in developing cementitious composites with high strength and toughness, but also effective in enhancing the piezoresistivity of the composites. In this study, four types of carbon nanofiber (CNF) were added at different concentrations up to 1.1 wt% in ordered to develop a more comprehensive study about the effect of CNF on mechanical, electrical and piezoresistive behaviour of cementitious composites. Besides, CNF was also added into the CF reinforced cementitious composites to study the effect of hybrid CNF/CF. The result showed that, although CNF can contribute to the mechanical properties of cementitious composites, hybrid CNF/CF is more effective in enhancing the compressive and flexural strength and improving the electrical conductivity of the composites. In terms of piezoresistivity behaviour, composites with both mono CNF and hybrid CNF/CF demonstrated a reversible piezoresistive behaviour and presented a linear relation between the fractional change in resistivity (FCR) and applied load. Composites containing mono CNF showed smooth curves with no obvious noise, however, the maximum FCR is about 50% and obvious time drift can be observed due to polarisation. Although the addition CNF reduce the sensitivity of the piezoresistive response compared to composites containing CF alone, hybrid CNF/CF seemed to be more effective in increasing the sensitivity of the composites compared to mono CNF. A higher maximum FCR around 80% can be achieved by composites containing hybrid CNF/CF. Besides, the piezoresistive behaviour of hybrid CNF/CF reinforced composites showed good stability and repeatability. These findings suggest that hybrid CNF/CF may be a promising additive to develop self-sensing cementitious composites.