4. Conclusions
Conductive asphalt concrete with a suitable amount of graphite powder and carbon fibre can effectively diagnose its own strain during the loading process and resulting damage. (1) The resistivity changes are a negative pressure resistance effect in which resistivity decreases as the load increases and back to the initial state after unloading. Although the variation of the absolute value of each cycle in resistivity may not be consistent because of the influence of noise and changes in the structure, the changes in the resistivity of frequency and load frequency are equal, demonstrating that the resistivity of each cycle changes in response. (2) Conductive asphalt concrete has excellent self-monitoring capabilities of internal damage, and there are three distinct stages of resistivity changes during the destruction process of the specimen. In the initial stages of loading, the contact between the mixture becomes tighter because the conductive asphalt concrete specimen is subjected to loads, forming a more conductive path, and the resistivity decreases sharply. In the second stage, asphalt concrete is deformed smoothly. In this process, small changes in the internal structure of the asphalt concrete result in small changes in resistivity. In the final stage, the progressive development of cracks in asphalt concrete leads to the complete destruction of the specimen. Conductive paths are seriously damaged, resulting in a sharp increase in resistivity; the change in resistivity exceeds 50%. (3) The resistivity change is related to internal carrier concentration. Resistivity is inversely proportional to carrier concentration. The smart mechanism is due to changes in the carrier concentration per unit volume. (4) CT identification can confirm that resistivity change is caused by material changes in the internal structure of the process of fatigue failure. The decrease or increase in resistivity is the result of the decrease or increase of internal porosity.
