A critical review of electrical-resistance-based self-sensing in conductive cement-based materials

Self-sensing refers to a structural material sensing itself. It is valuable for smart structures. It is mainly achieved by measuring the electrical resistance of the structural material, as the resistance is affected by strain and damage. Electrical-resistance-based strain/damage self-sensing in cement-based materials emerged in 1993 and the field has grown greatly since then. This is a critical review of this field. Elastic strain causes reversible resistivity change. Damage causes irreversible resistivity increase. Conductive admixtures are required. For short carbon fiber as admixture, the resistivity decreases upon compression, due to the fiber-matrix interfacial resistivity decrease, and increases upon tension; upon flexure, the compression surface resistance decreases and tension surface resistance increases. As shown by the gage factor, carbon fiber/nanofiber/nanotube is more effective than carbon-black/graphite-nanoplatelet/graphene, and short carbon fiber is more effective than carbon nanotube. The addition of carbon nanotube to short carbon fiber decreases the gage factor. For nanotube/ nanofiber, the resistivity decreases upon compression, due to increased contact among the nanotube/nanofiber units. The sensing performance is best when the admixture volume fraction is near the percolation threshold. Silica fume and surfactants in the cement mix promote the admixture dispersion. Sonication for promoting the nanocarbon dispersion is not necessary for the fiber dispersion. Nanofiber/nanotube deposition on fine aggregate enhances the dispersion. Macroscale steel fibers are less effective than microscale ones, which are less effective than carbon fiber. Common experimental method pitfalls are also addressed. The four-probe method is much more reliable than the two-probe method.