Moisture-dependent capacitance-based stress sensing in asphalt for smart infrastructure applications

This study investigates the effect of moisture on the capacitance-based stress self-sensing performance of asphalt, which is used as a pavement material without any conductive admixtures. To examine this effect, fully saturated specimens were gradually dried to achieve moisture levels of 20% and 0%, and these specimens were tested. Cylindrical asphalt specimens (100 mm diameter × 60 mm height) were tested using curved aluminum foil electrodes placed around the surface. Capacitance was measured transversely. The specimens were subjected to low (0.8−3.85kPa) and relatively high (9−44.85 kPa) stress levels while their capacitance values were recorded. The results indicate that the capacitance value increases with higher moisture content, with measured values of 13.55 pF, 17.00 pF, and 58.15 pF for specimens with 0%, 20%, and 100% moisture content, respectively. Regardless of moisture content, the capacitance values changed upon loading. Test results indicated that under low-stress conditions, the peak fractional change in capacitance at 3.85 kPa was measured as approximately 3.0%, 2.6%, and 0.6% for specimens with 0%, 20%, and 100% moisture content, respectively. Under high-stress conditions (44.85 kPa), the corresponding fractional changes in capacitance were recorded as 16.7%, 11.4%, and 6,4%, respectively. The capacitance decreases upon the axial compression. These findings highlight the influence of moisture on capacitance-based sensing. It was concluded that asphalt material can serve as an effective stress indicator under known moisture levels.