Influence of Carbon Nanotubes Dispersion Degree on the Piezo-Resistive Behavior of Self-sensing Cementitious Composites

Literature reports indicate that Carbon Nanotubes (CNT) are one of the best conductive fillers for self-sensing cementitious composites (SSCC) due to their excellent electrical conductivity. However, due to their Van der Waals interactions and hydrophobic nature, it is a challenge to properly disperse them throughout the cement matrix. Among the known dispersion methods, the use of ultrasonic energy in aqueous media, combined with superplasticizers, has been found to yield good performance. Nevertheless, high amounts of ultrasonic energy can damage the structural integrity of CNT and modify their electrical properties. This work explores how the CNT dispersion degree, obtained from the use of different amounts of ultrasonic energy in aqueous media, affects the self-sensing response of SSCC. CNT aqueous solutions were sonicated in presence of a naphthalene-based superplasticizer and evaluated by means of UV-Vis spectroscopy to characterize their dispersion degree. Cement pastes with different CNT contents were manufactured for each sonication energy and submitted to resistivity and piezo-resistivity testing. Satisfactory self-sensing results were obtained using both high and low sonication energies, associated with good and poor dispersion degrees of the CNT respectively. It was concluded that poorly dispersed CNT can be used to manufacture SSCC by adjusting the CNT concentration.