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Electrically conductive asphalt composites have immense potential for various multifunctional applications such as self-healing, self-sensing, snow and ice removal, and energy harvesting, and controlling asphalt conductivity is the first step to enable such applications. Previous investigators have used conductive fibers as major conductive additive for asphalt composites, and the sudden transition from the insulated phase to the conductive phase, known as the percolation threshold, is commonly observed. Since the percolation threshold hinders precise control of asphalt conductivity, it is imperative to mitigate the sudden transition in the electrical resistivity curve to enable practical applications of asphalt composites. Some recent publications showed the potential of graphite in mitigating the sudden transition. The study presented herein investigates possibility of precisely controlling the electrical conductivity of asphalt concrete only by adding filler size graphite powder. Nine different types of graphite having different particle shapes and sizes are selected to investigate their effect on conductivity control. The volume resistivity of the asphalt mastic specimens containing various concentrations of graphite is evaluated. In addition, scanning electron microscope analysis is conducted for the graphite particles to provide physical explanation for their different effects on imparting conductivity. The results show that the electrical resistivity of asphalt mastic is significantly varied with the types of graphite. The mastics containing natural flake graphite show gradual decrease in volume resistivity as the graphite content increases, and sufficiently low resistivity can be obtained in the specimens with natural flake graphite. On the other hand, amorphous graphite is not efficient in reducing volume resistivity. Graphite with high surface area presents difficulty in mixing. In the next stage of research, two best performing graphite out of the nine different types are selected to be added to asphalt concrete, and the effect of aggregates on electrical resistivity is examined. It is found that flake graphite 516 provides good electrical conductivity along with improved mechanical performance of asphalt concrete. Thus the study provides fundamental information on the selection of graphite type and amount to achieve proper electrical conductivity required for multifunctional applications.

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Impact diamonds were found in several impactites from the Ries crater, Germany including fallout and fallback (crater fill) suevites. a glass bomb, impact melt rock and shocked gneiss. These diamonds formed two distinct grain size populations: 50-300?m apographitic. platy aggregates with surface ornamentation and etching that were observed using optical and scanning electron microscopy and 5-20?m diamonds which displayed two different morphologies identified using transmission electron microscopy and selected area electron diffraction. These 5-20?m grains comprised apographitic. platy grains with stacking faults, etching and graphite intergrowths together with elongate skeletal grains with preferred orientations to the individual crystallites. Thermal annealing of stacking faults and surface features was also detected. Stepped combustion combined with static mass spectrometry to give carbon isotopic analysis of individual diamonds. graphite and acid-residues indicate that the primary carbon source is graphite. This graphite was found to be 13C depleted with respect to similar samples from the Popigai impact crater. The admixture of presumably carbonate derived carbonaceous material is suggested to account for the 13C-enriched ?13C compositions encountered in whole-rock suevites known to include carbonate melts. On the basis of morphology. mineralogical associations diamond/graphite ratios and carbon isotopic compositions three possible formation mechanisms for impact diamonds are suggested: fast. high temperature conversion of graphite following the passage of the shock wave, a vapour phase condensation or growth within substrate minerals or an orientated stress field and the incomplete transformation of a mixture of amorphous and crystalline graphite. Further more exotic mechanisms such as intermediary carbyne phases cannot be discounted. Impact diamonds, 1-5?m in size. were also identified in suevite residues and a black matrix lithic breccia from the Gardnos impact crater. Norway. The carbon isotopic compositions are in agreement with previous measurements of whole rock samples with a small 13C-enriched component probably representing diamond.

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