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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, Regarding the cyclic voltammetry (CV) measurements, it consists in applying a cyclic voltage with a triangular waveform and measuring the produced electric current. The results of cyclic voltammetry are usually presented in the form of current–potential curves as in Figure 1c. Aditionally, the capacitance C of the samples can be obtained as: C = 1 i ( v ) d v , (1) 2 s r ∆ v The selected rGO powder has an average thickness of 5 atomic layers of carbon, and it was synthesized at the “Laboratorio de Espectroscopia Ato´mica Molecular” (LEAM) of the “Universidad Industrial de Santander / Colom- bia”, following the modified Hummers’ method described in Marcano et al. Marcano et al. (2010). Moreover, the admixture included general-purpose Portland cement manufactured according to the standard ASTM C1157 ASTM International (2010), ultrapure water obtained from a Milli-Q IQ 7000 apparatus, and two copper desoldering wires of diameter 3 mm employed as embedded electrodes. Three identical cylindrical specimens per method following the proportions in ASTM International (2018) (6 cm in length by 3 cm in diameter) were prepared by mixing graphene powder (at 0.14%wt) previously dispersed in ultrapure water (from Milli-Q IQ 7015) with Portland cement. One of the dispersion methodologies (Method 1, i.e., M1-sonicator dispersion) involved using a 40 kHz Branson 1800 ultrasonic cleaner for a period of 2 h. Additionally, the second dispersion methodology (Method 2, i.e., M2-ultrasonic tip set) was implemented using an ultrasonic tip set. The oscillation amplitude was configured to 40% at an energy of 4500 J for 100 g of dispersion (or 45 J / g), with on / o ff cycles of 20 seconds each. It’s worth noting that significantly less energy per gram of dispersion was used compared to the previous work by Triana-Camacho et al. Triana-Camacho et al. (2023). Subsequently, the cement-based compound was allowed to dry in the molds for 24 h at room temperature, followed by a 28-day curing period and an eventual drying in an oven for 24 h at 50°C. 2.2. Charaterization of the specimens The equipment used for the electrical characterization was a Potentiostat PST-11 from DinTech manufacturer, and displacement-controlled compression tests were carried out with a universal testing machine Servosis ME 405 to characterize the mechanical properties of the composite. Then, a series of experiments with step voltages from -0.5 V to + 0.5 V were conducted on the rGO specimens for their electrical characterization (Figure 1(a)). The decay of each of their current responses (current transients) is observed in Figure 1(b), followed by an indexing or sampling for all current transients at a time τ (this time must be constant for all analized transients), which normally allows obtaining a current versus potential curve once the step reaches its final value (Figure 1(c)). In this case, the current transients i(t) were integrated to obtain the electrical charge Q. Finally, Q was derived to get the capacitance as a function of the step voltages. with the plain cement matrix Madbouly et al. (2020). Furthermore, concerning their electromechanical properties, low concentrations of rGO can increase the piezoresistive sensitivity up to 3.66% per MPa under compressive or ten- sile stress Qi et al. (2023). This piezoresistivity property can be exploited to generate load-bearing strain sensors, in virtue of which the material exhibits variations in its electrical conductivity under the action of a mechanical strain. Even more promisingly, recent studies have revealed that rGO-cement composites also exhibit piezoelectric proper- ties Long (2023); Pan et al. (2022); Triana-Camacho et al. (2023). This property opens rast possibilities for developing self-powered strain sensors, bypassing the power supply requirements of electrical resistivity settings in piezoresistive sensors. RGO-cement-based composites have been investigated using cyclic voltammetry (CV) and sampled cur- rent voltammetry (SCV), two voltammetric methods commonly used in electrochemistry for studying the electron transfer kinetics of electrochemical reactions with electrode materials Rodr´  guez and Denuault (2021). In this study, a capacitive change has been obtained by conducting simultaneously staircase compressive essays and electrical charac- terization. However, the paramount contribution of this investigation lies in the establishment of a novel methodology for electrical assessments aimed at delineating the piezocapacitive attributes of cement-based composites. 2. Methods 2.1. Materials and specimens