PSI - Issue 67

Daniel A. Triana-Camacho et al. / Procedia Structural Integrity 67 (2025) 47–52 D.A. Triana-Camacho et al. / Structural Integrity Procedia 00 (2024) 000–000

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(a) (c) Fig. 1. Voltamperometry of sampled current (SCV); (a) applied step potential; (b) current responses of the specimen; (c) construction of the sampled current voltammogram. (b)

where i is the electrical current, v the voltage, s r the scan rate conducted at 25 mV / s, and ∆ v the voltage di ff erence 1 V for a window from -0.5 V to 0.5 V. In parallel with the electrical characterization, the rGO-cement composites underwent displacement-controlled compressive loading, ranging from 0.5 to 2.5 kN, to assess the capacitive properties of the specimens and their sensi- tivity to the applied strain (the strain was computed from the displacements of the testing machine). Finally, 1 cm cubes were cut from the rGO-cement composites for physicochemical characterization using Scanning Electron Microscopy with Energy Dispersive X-ray Spectroscopy (SEM / EDX). 3. Results The growing up of hydration crystals onto graphene sheets rich in carboxyl groups has been documented in the reference Zhao et al. (2020). The significant calcium content (16.51 wt%) observed from EDS results in Figure 2, as determined by Energy-Dispersive X-ray Spectroscopy (EDS), corroborates the pronounced a ffi nity between calcium ions and both Si-O hydration products and -COO groups Zhao et al. (2020). Moreover, EDS analysis revealed elevated concentrations of oxygen (14.44 wt%) and carbon (51.08 wt%), indicative of the presence of rGO Dong et al. (2022), which form laminar structures as it appears in Figure 2. Until a few decades ago, it was not believed that materials could exhibit quantum behaviors at temperatures above extremely low levels. However, graphene has demonstrated ambipolar electrical properties, allowing positive and negative charges to move separately through the graphene sheets. This behavior is reflected in a V-shaped conductance profile Lopes et al. (2021), as observed in Figure 3. Additionally, V-shaped capacitance behavior has before been evidenced through capacitance spectroscopy (CS) in the literature Lopes et al. (2021). This fact can be explained quite simply as follows: two di ff erent energies (depicting as a voltage) can produce a mirrored behavior in the conductivity or electrochemical capacitance around the equilib- rium energy of the system, as demonstrated by Lopes et al. Lopes et al. (2021) using graphene on a silicon / silicon oxide substrate. Although there is a significant di ff erence between Lopes’ system and ours, the distribution of graphene in the bulk of cement also allows us to elucidate both properties, which can be explained by classical and quantum physics. Classical electric properties are exhibited when the fiber concentration is above the percolation threshold. At the same time, quantum properties emerge below the percolation threshold, as described in the work of Buroni and Garc´  a-Mac´  as Buroni and Garc  a-Mac´  as (2021) for carbon nanotubes-cement-based composites. According to these arguments, the curve corresponding to the specimens prepared using Method 2 (see Figure 3) exhibits a symmetrical double capacitance behavior around the equilibrium state ( ∼ 0 V), and therefore with a greater quantum nature. This indicates better dispersion of the graphene sheets and a lower presence of percolated pathways. On the other hand, the specimens prepared with Method 1 show lower capacitance and a completely reversed behavior as expected in semiconductor materials with non-linear capacitance Lee et al. (2019). In Figure 4(a), the capacitance curves against compressive load of the specimens prepared using M1 and M2 are ob- served. Similar to the case without compressive load (see Figure 3), M2 maintains higher capacitance values compared