PSI - Issue 28

Angeliki-Eirini Dimou et al. / Procedia Structural Integrity 28 (2020) 1679–1685 Author name / Structural Integrity Procedia 00 (2019) 000–000

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applications, since nanoparticles tend to agglomerate in solutions. This phenomenon leads to the reduction of the specific surface area of the particles as well as an inhomogeneous dispersion in cement, e.g. in Zare et al. (2017). In order to overcome this issue, the application of ultrasonication energy is necessary. For example, Peng et al. (2019) dispersed GO in water with the addition of superplasticizer and ultrasonicated the mixture for 5 min before adding it in cement. Vallejo et al. (2018) studied dispersions of chemically modified graphene nanoplatelets that underwent ultrasonication for 200 min in an ultrasound bath. Baig et al. (2018) state that tip sonicators exhibit a much higher power than a bath sonicator but produce high-quality graphene in short time. The present work focuses on the first step of the production of rGO/cement composites, i.e. the creation of the aqueous nanoparticle dispersion as a step before it is added in the cement. In the present study, six rGO dispersions were produced based on different concentrations of the binder. Ultrasonication energy with a probe sonicator is applied on all dispersions and their electrical properties are measured through the application of Electrical Impedance Spectroscopy during ultrasonication. The goal of this study is to highlight the potential use of EIS as an on-line method to evaluate the dispersion control so as to find the optimal conditions (concentration, sonication energy) for the proper dispersion to be incorporated in the cement matrix.

Nomenclature CBNs

carbon-based nanomaterials electrical impedance spectroscopy

EIS rGO GO

reduced graphene oxide

graphene oxide

2. Materials and Methods 2.1. Materials

The nanomaterial rGO was produced at the Department of Materials Science & Engineering, University of Ioannina and under the framework of the research project “Self-healing and self-sensing nano-composite conservation mortars – AKEISTHAI”. rGO was received from the reduction of GO. 2 g GO were dispersed in 1000 mL distilled water under magnetic stirring for 1 h and 4 g NaBH 4 were stirred in 500 mL distilled water for 20 min. The two dispersions were mixed and dispersed together for 2 h at 80 o C. The dispersion was centrifuged in 6000 rpm for 10 min. Finally, the solid part was collected and dried at room temperature. The dispersion medium in this study was water. The water samples used were produced by Epirotic Bottling Industry S.A. (VIKOS S.A.). The characteristics of this water are given in Table 2.

Table 2. Characteristics of natural mineral water VIKOS S.A. Physical Properties

Value

pH

7.3

Conductivity

480 μS/cm (25 o C)

Total Hardness (CaCO 3 ) Total Dissolved Solids

240 mg/L 268 mg/L

2.2. Methods

2.2.1. Dispersion process Six dispersions were prepared containing different rGO concentration and water. The exact rGO quantities are based on the amount of the binder, in which the dispersion will be added as a future step, and they are given in Table 3 3. The materials were weighed and placed in a beaker and were hand-stirred before being subjected to sonication.