Pulverised CFRP waste and reclaimed carbon fibre for cement-based sensors: Investigating electrical resistivity and piezoresistivity under varying environmental conditions

Abstract

Cementitious composites with carbon fibres (CFs) have been developed as functional cement-based sensors for real-time structural health monitoring (SHM). However, few studies have investigated the piezoresistive performance of these cementitious composites under different external environmental conditions. This research studies the influence of carbon fibre-reinforced polymer (CFRP) recyclates on the electrical resistivity and piezoresistivity of cementitious composites under varying temperature, humidity and chloride-induced corrosion. The experiments involved the use of recycled carbon fibre (rCF) reclaimed through acid solvolysis and recycled CFRP (rCFRP) derived from mechanical recycling. Their performance in cementitious composites was evaluated against benchmarks containing virgin carbon fibre (vCF) offcuts and plain mortar without additives. The results show that while incorporating rCFRP increased the electrical resistivity of cementitious composites compared to those with CFs, the rCFRP specimens demonstrated more consistent and repeatable piezoresistive behaviour under cyclic loading in both low and high-humidity environments. Under 30 % humidity conditions, the rCFRP specimen achieved an average stress sensitivity (SS) of 0.42 %/MPa and a gauge factor (GF) of 17.50. The piezoresistivity decreased after exposure to chloride-induced corrosion. However, the behaviour remained stable through a well-distributed conductive network, which proved more effective than ionic conduction pathways. These findings demonstrate the potential of rCFRP-based cementitious sensors for SHM applications, offering both technical effectiveness and environmental sustainability.