Preparation And Research Of Electrically Conductive Asphalt Concrete

Asphalt concrete has been extensively applied in expressway and runway of airfield. It belongs electrical insulating material with a resistivitvy of 107~109om. The conductive behavior of asphalt mixture can be improved with the addition of conductive materials, thus a multifunctional Asphalt concrete can be obtained, which would have a profound effect on pavement deicing, damage testing, highway traffic monitoring and so on.Superpave design method was employed to design the mix proportion of electrically conductive asphalt concrete (ECAC). The curve of mix proportion kept away from the restricted zone in order to provide enough voids in mineral aggregate (VMA) to fill the high content of conductive materials. Conductive powder can regard as a part of filler in asphalt concrete. But they need to make a conversion for equal quality of limestone powder because of the deference of the density. The conductive behavior of asphalt mixture can be improved by adding carbon black, graphite and carbon fiber. The absorbing oil nature of carbon black, the lubricated effect of graphite and the bad dispersion of carbon fiber limit their application in ECAC respectively. The improving effect of graphite on the resistivity of ECAC is excellent, and the composite modification with other conductive materials also is obvious. Graphite was used as main component, and a few carbon fibers were added as assistant component. Carbon black replaced a part of limestone powder, which has an enforcement effect on asphalt concrete. The conductive performance of conductive powder filling asphalt concrete is improved by adding a few chopped carbon fibers. Carbon fibers play a role of the conductive bridge effect and the short circuit effect because of high long/ diameter ratio, improving the conductive mechanism of electron.Percolation Theory can explain the formation of conductive passages under the dependence of the conductivity and graphite content in ECAC. The conductive behavior of ECAC was analyzed by tunnel effect. So the conductive behavior in AC field was equivalent with the parallel connection of a resistor and a capacitor, the nonlinearity of V - I characteristics originate from a combination of the implication of the nonlinear contribution of tunnel conduction between graphite particles and the production of additional conducting pathways under sufficiently strong local fields, which is the function of the gap between graphite particles andhas a relation with the transition ability of electrons.Graphite absorbs asphalt in liquid state strongly. The evaluation of volume performance of ECAC must take absorbed asphalt into account. Experimental results of Marshall Remnant Stability Test, Water Susceptibility Tensile Strength Ratio (TSR) Test and Rutting Test show that graphite modified ECAC possesses of high anti-water damage ability and excellent high-temperature stability, which is expected to apply as new-type pavement. Stable conductive performance can be achieved by controlled graphite content and asphalt content and increasing the compact degree. Piezoresistivity of ECAC may involve proximity effect, microcrack and the staggered arrangements of conductive pass-ways due to shear strength of aggregates. The T-R characteristics may originate from the total function of volume expansion and temperature susceptibility of asphalt, the deference of volume expansion coefficient with heat between asphalt and graphite, and internal stress.