Self-Sensing Concrete Mixes with Multiwalled Carbon Nanotubes: Influence of Dosage and Flexural Sensing Performance in RC Beams

This research investigates the application of multiwalled carbon nanotube (MWCNT)-enhanced concrete for self-sensing and structural health monitoring (SHM) in civil engineering. Concrete specimens of different grades (M25, M30, M40, and M50) were prepared with varying MWCNT dosages (0.3%, 0.4%, 0.5%, and 0.6% by weight of cementitious material) and tested for compressive strength and electrical resistance to identify the optimal MWCNT content that maximizes sensing performance while maintaining mechanical integrity. The change in electrical resistance of the MWCNT-enhanced self-sensing concrete under load is expressed as the fractional change in resistance (FCR). The onset of microcracking is indicated by a distinct change in the trend of FCR variations during loading. It was found that the same MWCNT dosage yields the highest self-sensing performance across all concrete grades. To further assess sensor performance, a concrete sensor of dimension 25 mm × 25 mm × 200 mm —composed of M25 grade mix with 0.5% MWCNT and aggregate of maximum size 6 mm—was embedded in the tension zone of reinforced concrete (RC) beams. Flexural tests were conducted on four beam configurations: (1) beams with standard concrete; (2) beams completely made with self-sensing concrete; (3) beams with a 30 mm layer of self-sensing concrete at the tension zone; and (4) beams incorporating the fabricated sensor. It was observed that, with increasing load, the FCR follows the same trend as the strain does. The study aimed to determine whether the discrete concrete sensor outperforms other configurations under flexural loading. The results indicate that incorporation of the concrete sensor yields sensing performance that is at least comparable—and often superior—to the alternatives.