Optimizing the self-sensing properties of alkali-activated conductive mortar with aligned nickel-coated carbon fibers

Self-sensing concrete (SC), a composite material integrating structural and sensing functions, plays a key role in the development of intelligent concrete infrastructure. This study presents an innovative method using alkali-activated materials (AAM) as binders and nickel-coated carbon fibers (NCFs) as conductive fillers to improve the self-sensing properties of alkali-activated conductive mortars (AACMs). The influences of fiber orientation (random, parallel, vertical) and NCF content (0–0.3 %) on the electrical conductivity and piezoresistive properties of AACMs were investigated. Scanning electron microscopy (SEM) and optical microscopy were used to analyze the fiber-binder interface and fiber orientation factor. The results indicated that replacing carbon fibers with NCFs significantly reduced the resistivity of AACM, while AACM exhibited anisotropic electrical properties after fiber orientation. Parallel-oriented AACM exhibited low resistivity (97.97 Ω cm) and superior piezoresistive performance under cyclic loading, achieving a peak FCR of 26.1 % and GF of 394.05, demonstrating excellent signal reversibility, repeatability, and stability, while vertical orientation had an adverse effect. With the assistance of fiber alignment, AACM with a small NCF content (0.1 vol%) greatly enhanced the piezoresistive performance. A linear correlation was found between the orientation factor, conductivity, and piezoresistive properties, confirming the role of fiber alignment in optimizing the self-sensing performance of AACM.