Exploring the Capacitance-Based Stress Self-Sensing Mechanism in Geopolymer Mortar and Its Correlation with Stress Levels

In this study, the capacitance-based stress self-sensing properties of fly ash-based geopolymer mortar are investigated for the first time. A coplanar electrode configuration is employed for capacitive measurements. Variations in capacitance are determined by subjecting the geopolymer mortar to both low (1.34–6.7 kPa) and relatively high (5.37–26.85 kPa) cyclic stress regimes. Before the tests, the capacitance and resistance of the test specimen are measured, yielding values of 412.7 pF and 34.17 kΩ, respectively. As stress levels progressively increase, the capacitance gradually decreases, and the resistance gradually increases. Specifically, the stress sensitivity, represented as the fractional change in capacitance per unit stress, is found to be 1.8 × 10⁻⁷ P⁻¹ for low-stress regimes and 1.3 × 10⁻⁷ P⁻¹ for high-stress regimes. It is worth noting that capacitive stress self-sensing is observed to be more effective in low-stress conditions.