Fiber research in concrete construction is an ongoing field and the use of carbon nanofibers (CNF) will be examined in this study. Fibers improve brittle materials such as concrete by enhancing tensile strength, ductility, toughness and conductivity. Short-fiber composites are a class of strain sensor based on the concept of short electrically conducting fiber pull-out that accompanies slight and reversible crack opening. For a fiber composite to have strain sensing ability, the fibers must be more conducting than the matrix in which they are embedded, of diameter smaller than the crack length, and well dispersed. Their orientations can be random, and they do not have to touch one another. The electrical conductivity of the fibers enables the DC electrical resistivity of the composites to change in response to strain damage or temperature, allowing sensing. Because of the high cost associated with CNF, a CNF aggregate (CNFA) was developed. The CNFA is 2.54 cm × 2.54 cm × 2.54 cm (1.00 in. × 1.00 in. × 1.00 in.) so that it is roughly the same size as a normal aggregate found in the concrete matrix. The CNFA consists of a mortar containing dispersed CNF, is self-sensing, and can be used to determine the damage in the CNFA. The CNFA can be embedded in reinforced or prestressed concrete structures and used to determine the localized strain in a structure for implementation of structural health monitoring in full-scale bridges and buildings.
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