Self-Sensing Performance of Cementitious Composites with Carbon and Recycled Carbon Fibres

This paper investigates the electrical-mechanical performance of cement-based mortar and concrete mixes incorporating carbon and recycled carbon fibres. Mortar mixes were produced with varying fibre content from 0.1% to 0.5% by volume for both types of fibres, while sand/cement and water/cement ratios were kept constant to achieve a similar composition in terms of mortar matrix. Concrete mixes were also produced incorporating 0.5% vol. of fibres and varying the ratio of coarse/fine aggregates from 1 to 2. Electrical measurements and mechanical characterisation tests were performed at 28 days while cyclic compression tests with concurrent measurements of electrical resistance were carried out to assess the piezoresistive response. The percolation threshold in both virgin and recycled carbon fibres was found to be approximately 0.1% vol. in mortar mixes, with mortars reinforced with recycled fibres showing higher sensitivity. The addition of higher amounts of coarse aggregates fibres led to a non-homogenous distribution of fibres within the mortar matrix and limited the piezoresistive response of the composite. The results highlight the potential of recycled carbon fibres in substituting expensive inclusions in smart applications, without compromising electrical and piezoresistive performance.