Short carbon fiber reinforced epoxy coating as a piezoresistive strain sensor for cement mortar

Epoxy containing 10 vol.% short carbon fibers and applied as a coating (0,2 mm thick) directly on cement mortar was found to be an effective piezoresistive strain sensor for tensile strain up to 0.042% and compressive strain down to -0.11%. Exceeding these strain limits caused damage in the coating. The strain sensitivity (reversible fractional increase in electrical resistance per unit strain) was 94-97 and 20-24 when the strain was contraction and expansion, respectively. The irreversible fractional increase in resistance per unit strain was 0.5-2.3 and 15-69 when the strain was contraction and expansion, respectively; it increased with increasing magnitude of strain. The resistance change was almost totally reversible when the strain was contraction, but was only partly reversible when the strain was expansion. The sensor in coating form was similar to that in bulk form in the electromechanical behavior.