3.1.3. Conductivity

Figure 2f illustrates the conductivity (*σ*) results of the GRGC specimens. The conductivity values increase with the increase in GO dosage and range between 6.05 × <sup>10</sup>−<sup>14</sup> and 7.72 × <sup>10</sup>−<sup>13</sup> <sup>Ω</sup>·mm−<sup>1</sup> for GRGC0 and GRGC4 at low frequencies of (101) Hz, respectively. The in situ reduction of GO improved electrical conductivity properties and contributed to enhancing GRGC conductive properties. At higher frequencies (i.e., 105 Hz), (*σ*) increased for all GRGC specimens, and the corresponding values include 1.18 × <sup>10</sup><sup>−</sup>12–2.27 × <sup>10</sup>−<sup>12</sup> <sup>Ω</sup>·mm<sup>−</sup>1. At lower frequencies, the (*σ*) of the GRGC specimens remained approximately constant. However, the increment in conductivity is significantly higher when the frequency is more than 104 Hz. This occurrence could be associated with the geopolymerisation reaction. The study by Hanjitsuwan et al. detected the same trend of increased conductivity for the geopolymer pastes with increased frequencies [17,18]. The molecular structure of geopolymeric gel is attributed to the increment of electrical conductivity at higher frequencies, mostly

via the Na+ ion hopping mechanism between the cation sites. A higher dosage of graphene in geopolymer composites leads to higher conductivity. Still, a significant increase in conductivity was observed at higher frequencies, which could be explained via the combination of Na+ ion hopping and the electronic conductivity of in situ reduced GO, leading to the shortening of conduction distance. Thus, GO could be considered an effective agent for improving the (*σ*) of geopolymer composites for different applications [12]. The relationship between the (*Z*) and (*σ*) curves demonstrates the homogenous dispersion of GO in the geopolymer matrix since the agglomeration of GO could lead to improper conductivity in the GRGC specimens. The results also suggest that there might be a percolation threshold between 0.1 and 0.2 wt.% GO addition in the GRGC matrix. The manifestation is evident via the slight difference in the behaviour of curves in Figure 2b,f. Therefore, it can be considered that conductive fillers such as GO largely facilitate conductivity in geopolymer composites and can be tailored for appropriate piezoresistive responses according to the required applications.

**Figure 2.** *Cont*.

**Figure 2.** Influence of GO on different electrical parameters of geopolymer composites: (**a**) capacitance, (**b**) impedance, (**c**) dielectric constant, (**d**) dielectric loss, (**e**) tan delta and (**f**) conductivity.

### **4. Conclusions**

In this study, different dosages of low-cost GO were incorporated in geopolymer composites to fabricate sustainable GRGC specimens for various smart applications. SSIS investigations were conducted at room temperature to characterize and assess the significant dielectric properties of GRGC specimens, which are concluded as follows.

The interaction of the GO sheets with the alkaline activator in geopolymeric reactions produced highly reduced and cross-linked GO sheets, enhancing the electrical conductivity properties of the composites.

At 101 Hz, GRGC specimens with 0.4 wt.% GO obtained a maximum ionic/electrical conductivity of 7.72 × <sup>10</sup>−<sup>13</sup> <sup>Ω</sup>·mm−<sup>1</sup> and a minimum impedance of 4.36 × <sup>10</sup><sup>5</sup> <sup>Ω</sup>, suggesting desirable low-frequency-based applications.

A percolation threshold was observed between 0.1 and 0.2 wt.% of GO introduction in the geopolymer matrix.

Increasing the GO dosage up to 0.4 wt.% aided in reducing the electrical impedance of GRGC specimens up to 91.81%.

**Author Contributions:** Conceptualization: R.S.K.; methodology: R.S.K.; formal analysis: R.S.K.; investigation: R.S.K.; resources: S.M.M.; writing—original draft preparation: R.S.K., S.S. and K.K.; writing—review and editing: T.S.Q. All authors have read and agreed to the published version of the manuscript.

**Funding:** The first author would like to acknowledge the funding of 500\$ received through the ASTM International Student Project Grant Award 2021, USA.

**Institutional Review Board Statement:** Not applicable.

**Informed Consent Statement:** Not applicable.

**Data Availability Statement:** Not applicable.

**Acknowledgments:** The authors would like to thank Ashok Kumar Sahu and Muhammad Shahid Anwar of CSIR—Institute of Minerals and Materials Technology (CSIR-IMMT)—India, for the materials, facility and support necessary for the experimental work, along with the proofreading of the article. The authors are also grateful for Tanvir Qureshi's IFA New Starters Award at UWE Bristol, UK. The publication cost of this paper was covered with funds from the Polish National Agency for Academic Exchange (NAWA): "MATBUD'2023—Developing international scientific cooperation in the field of building materials engineering" BPI/WTP/2021/1/00002, MATBUD'2023.

**Conflicts of Interest:** The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
