Research On Smart Characteristic Of Conductive Asphalt Concrete

Asphalt concrete has been widely applied in the pavement of highway and bridge. The conductive behavior of asphalt mixture can be improved with the addition of conductive materials, thus the self-monitoring material can be obtained. The monitoring of strain is valuable for structural control and dynamic load monitoring for traffic control; the monitoring of damage is valuable for structural health monitoring and service life prediction. The combined ability to monitor both reversible strain and damage is particularly valuable in real-time fatigue damage monitoring under dynamic loading, because the strain cycle and the point within the cycle at which damage occurs can be identified.The continuous mixture proportion such as AC-20 and discontinuous mixture proportion such as Superpave 12.5 are all can be employed to prepare electrically conductive asphalt concrete (CAC). Experimental results of Marshall Remnant Stability Test, Four Point Bend Fatigue Test, Indirect Tensile Modulus Test and Rutting Test show that graphite modified CAC possesses of high resistance to moisture damage and resistance to fatigue damage, high resilient modulus and excellent high-temperature stability, which is expected to apply as new-type pavement. It is exponential relation between the resistivity and air voids of asphalt mixture. The resistivity varied with temperature because the expansion coefficient of asphalt and graphite are repugnant.By using Dynamic Indirect Tensile Test, Four Bend Fatigue Test and Rutting Test, the use of CAC containing graphite and carbon fibers for strain monitoring was investigated and shown to be effective. The electrical resistivity increases reversibly with increasing strain under the test. It has higher self-monitoring ability when the graphite content is lower (beyond the value of threshold) and higher load. CAC for interior damage monitoring was investigated and shown to be effective too. The resistivity change can be divided into three phases through fatigue process: The resistivity is deceased with the specimen was more compressed in the first phase, and then it changed little in the second phase because the specimen was in a steady state after compressed. Finally the resistivity is increased with the specimen was destructed gradually. The increase or decrease of resistivity can be thought is begot by the variation of internal structure of asphalt concrete. Compression action can form more conductive paths and the resistivity is decreased. In the meanwhile, material failure can cut conductive path and the resistivity is increased.When the conductive concrete was embedded into common asphalt concrete specimen as a partial structure function, the road performances were greatly improved compared with completely CAC and it still has excellent piezoreisitivity character. When the piezoresistivity from negative turn into positive, it is 10mm rutting depth critical value that influence driving comfortably and safely, therefore the deformation self-monitoring has specially important significance.CAC has highly sensitive piezoresistivity and the mechanism can be explained by the number variation of electronic carrier. When the loading is compressive stress, the strain becomes smaller and smaller, so the number of carriers higher than that of previous load, therefore the resistivity is decreased. When the loading is tensile stress, the strain becomes bigger and bigger, so the number of carriers lower than that of previous load, as a result, the resistivity is increased. It can be identified that the structure variation of CAC was responsible to the resistivity change by Computer Tomography damage detecting.