Noncontact strain sensing in cement-based material using laser-induced fluorescence from nanotube-based skin
Wei Meng,Sergei M. Bachilo,Jafarali Parol,R. Bruce Weisman,Satish Nagarajaiah
Abstract
This study explores the use of the recently developed "strain-sensing smart skin" (S4) method for noncontact strain measurements on cement-based samples. S4 sensors are single-wall carbon nanotubes dilutely embedded in thin polymer films. Strains transmitted to the nanotubes cause systematic shifts in their near-infrared fluorescence spectra, which are analyzed to deduce local strain values. It is found that with cement-based materials, this method is hampered by spectral interference from structured near-infrared cement luminescence. However, application of an opaque blocking layer between the specimen surface and the nanotube sensing film enables interference-free strain measurements. Tests were performed on cement, mortar, and concrete specimens with such modified S4 coatings. When specimens were subjected to uniaxial compressive stress, the spectral peak separations varied linearly and predictably with induced strain. These results demonstrate that S4 is a promising emerging technology for measuring strains down to ca. 30 με in concrete structures.
