AC impedance spectroscopy (AC-IS) analysis to characterize the effect of nanomaterials in cement-based mortars

Abstract

In spite of several studies on the inclusion of nanomaterial in cement, the understanding of its properties is still far from complete. In this sense, complementary techniques, including non-destructive AC impedance, are useful tools for furnishing important information about the microstructure evolution. In this work, the characteristics of AC impedance spectroscopy of cement mortar with the addition of graphene oxide (GO) and nanofibrillated cellulose (NFC) were measured and analyzed with an equivalent impedance circuit. Pastes characterization tests were carried out to assess physical, hydration development and microstructure properties: water absorption, volume of permeable pores, thermogravimetric analysis (TGA) and scanning electron microscopy (SEM). In addition, compressive strength tests for mortars were performed in this study. The parameters obtained from the equivalent impedance circuit, including the electrical resistance of the high-frequency arc and depression angle, are related to microstructure and compressive strength. The results showed that the addition of GO and NFC affects the electrical resistance value of the high-frequency arc, and influence the matrix porosity, which was corroborated by compressive strength measurements. The values for the depression angle also reveal that the nanostructures act positively on the homogeneity of the cementitious matrix. Results show that impedance spectroscopy can be an excellent solution to monitor the curing process of cementitious composites with nanoreinforcements, being able to detect changes in the evolution of the microstructure.