Influência da umidade nas propriedades elétricas de pastas de cimento automonitorantes com nanotubos de carbono

Abstract

This work aimed to manufacture a self-sensing cement paste with carbon nanotubes (CNT) and to evaluate the influence on the electrical properties of the composite due to the presence of water in the pores. The performance of 4 superplasticizers (SP) as CNT dispersion agents in aqueous media was evaluated using UV-Vis spectroscopy, ζ-potential, Raman spectroscopy and electrical resistivity. From stability and isothermal calorimetry tests, the most adequate CNT:SP ratio was studied to manufacture the pastes and characterize them in terms of selfsensing response. Finally, the influence of water in the pores of the self-sensing composite with different CNT contents was verified by electrical resistivity measurements, electrification time and self-sensing tests. Results showed that the chemically based naphthalene SP exhibited the best performance in the dispersion of CNT in aqueous media, being better used in the CNT:SP 1:1 ratio (by mass). The self-monitoring composites manufactured showed sensitivity to the displacements imposed by mechanical stress, demonstrating potential application as displacement sensors. It was found that the presence of water in the pores of the matrix decreased the electrical resistivity and sensitivity to rupture, as well as increased the electrification time and the sensitivity to mechanical stress of self-sensing pastes with CNT contents below the conductivity threshold. It was concluded that to eliminate the effects caused by the presence of water, the CNT content adopted must be chosen above the conductivity threshold