Development and characterization of self-sensing CNF HPFRCC

Abstract

Cement based brittle matrix composites that show deflection hardening called high performance fiber reinforced cementitious composites (HPFRCC) have the potential of offering high resiliency and environmentally sustainable benefits in numerous applications. HPFRCCs have been used in numerous applications; however, more information is needed to fully understand, predict the behavior, and add functionality to HPFRCCs. This experimental research program aims to develop and characterize a new type of HPFRCC, composed of polyvinyl alcohol microfibers, carbon nanofibers (CNF), and a high volume of fly ash to form a self-sensing HPFRCC. Processing of the CNF and the HPFRCC composite matrix are studied to ensure adequate fresh mix properties and fiber dispersion. The multi-functionality of the CNFs allow for increased mechanical properties and enhanced strain and damage sensing capabilities. Digital image correlation was used extensively to capture the tensile strain and provide a visualization of the behavior of the composite under increasing displacements. CNF contents of 0.167, 0.333, 0.5, and 1.0 % were studied. Through laser diffraction analysis, sonication of CNF in a CNF/water/superplasticizer solution was found to improve particle dispersion. Mechanical testing showed that dosages of CNFs less than or equal to 0.333 % increased compressive strength, tensile strength, and stiffness. CNF had little effect on tensile ductility and toughness. Piezoresistive self-sensing strain measurement was achieved in all specimens. The addition of CNF improved the strain-sensing and allowed for stronger correlations between measured strains and correlated gauge factors. Ultimately, a CNF content of 0.333 % showed optimal results in terms of enhanced mechanical properties and self-sensing behavior for strain.