Piezoelectric behaviour of hybrid engineered cementitious composites containing shape-memory alloy, steel, and carbon fibres under compressive stress cycles

•Piezoresistivity of hybrid ECCs subjected to compressive stress cycles was studied.•The combination of PVA with SMAF, SF, and CF was considered.•The maximum FCR was obtained when 0.3% of carbon fibres were used.•Highest correlation coefficient between FCR and strain was observed for 0.6% CF.•Hybrid ECC containing SMAF or SF exhibited an irreversible increase in resistivity. Fibre hybridisation can improve the performance of Engineered cementitious composites (ECCs). This study examines piezoresistivity, fresh properties, and mechanical behaviour of hybrid ECCs developed through the combination of polyvinyl alcohol (PVA) with shape memory alloy fibres (SMAFs), steel fibres (SFs), and carbon fibres (CFs) individually. The distribution of CFs and the formation of conductive networks within hybrid ECCs containing CFs were also analysed using scanningelectron microscopy. Compared to other composites containing CFs, the hybrid ECC with 0.6% CFs exhibited the best piezoresistive behaviour under compressive stress cycles since it showed the highest correlation coefficient between fractional change in resistivity (FCR) and strain, a narrower 98% prediction interval, and less noisy electrical signals. SEM images of this composite revealed that CFs were in contact in large scale and formed cross-linked clusters, indicating that the CF dosage was above the percolation threshold. In contrast to the composites containing CFs, hybrid ECCs with SMAFs and SFs exhibited an irreversible increase in resistivity, especially in wet condition, due to the polarisation effect. However, the hybrid usage of SMAFs or SFs with PVA significantly enhanced the flexural performance of ECC, whereas its impact on the first-cracking strength of ECCs was insignificant. In contrast, CFs enhanced the first-cracking strength at all CFs contents studied here and increased the flexural strength of composites at CFs content of 0.1% and 0.2%., beyond which the ultimate flexural strength decreased.