Carbon nanotubes and nanofibers as strain and damage sensors for smart cement

The present paper reports on the strain and damage sensing potential of carbon nanotubes and carbon nanofibers embedded in cement mortars. Prismatic and three-point bending specimens were prepared at various nano-inclusion concentrations for measurement of the material’s surface electrical resistivity, establishment of its electrical percolation threshold, assessment of its piezoresistive response under cyclic compressive loading and for damage detection under pure bending of the mortars. Percolation theory conditions were met at a tube concentration of ca. 0.6% by weight of cement while both nanotubes and nanofibers endowed smartness to the mortars which exhibited remarkable electrical sensitivity to applied load, with fully-recoverable electrical resistances varying in an inverse relation with compressive stress. The potential of nanotubes and nanofibers as damage sensors in percolated mortars was manifestedby dramatic increases of in situ electrical resistivity under three-point bending testing, at loading instances as early as the maximum load, hence providing timely failure warnings. Differences in the strain and damage sensing potentials of the two types of nano-inclusions is presented and discussed in the text.