Controlling Conductivity of Asphalt Concrete with Graphite
Philip Park, Younho Rew, and Aishwarya Baranikumar, August, 2014
Electrically conductive asphalt concrete has a huge potential for various multifunctional applications such as self healing, self-sensing, and deicing. In order to utilize the full spectrum of applications of electrically conductive asphalt composites, precise control of the asphalt mixture resistivity is needed. Most of the previous research using conductive fibers as the primary conductive additives observed a sudden transition from the insulated to conductive phase, commonly known as the percolation threshold, which obstructs more precise conductivity control. Aiming to control the electrical conductivity of asphalt concrete with a smooth transition from the insulated to conductive phase, the researchers have selected graphite powders as an alternative conductive additive in this study. Nine types of graphite having different particle shape, size, and origin were mixed with asphalt binders, and their effects on imparting conductivity were investigated. Based on the results, the research team selected two types of graphite and evaluated the effects on the electrical conductivity of asphalt concrete. The team also examined the effects of aggregate gradation, binder content, and binder type.
The results showed that the electrical conductivity of asphalt mastic is sensitive to the graphite type. The natural flake graphite is effective to mitigate the percolation threshold, and a sufficiently high conductivity can be achieved by replacing a part of the fillers with graphite (the conductivity ranged from 10−6 to 10−2/Ω•cm). The results also showed that the binder type does not make a significant change in the mixture conductivity, but the aggregate gradation brings approximately two order differences in the volume resistivity. Mechanical performance of the conductive asphalt is also an important factor for practical field applications. The indirect tension test results showed that the addition of graphite improves the indirect tensile strength up to 41 percent. The electrical and mechanical data obtained from this study provide essential information on the selection of graphite type and asphalt mixture design to achieve the proper electrical conductivity required for the probable multifunctional applications of asphalt concrete, which will lead to technical innovations for sustainable pavements.
Keywords: Electrical Conductivity Control, Graphite, Asphalt Concrete, Percolation Threshold
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