Nano fibrous carbon produced from chromium bearing tannery solid waste as the bitumen modifier

Bitumen binders play a major role in reducing the aging and oxidation property of bitumen. Carbon nanomaterials act as an effective bitumen modifier due to its stiffness and strength. Thus, nano fibrous carbon (NFC) was prepared from Chrome Tanned Buffing Dust (a solidwaste generated from leather industries) with proper care of avoiding oxidation of Cr(III) to Cr(VI) through pulse pyrolysis system. Morphology analysis using TEM confirmed the nano fibrous structure of NFC. XRD pattern of NFC depicts the graphitic phases of carbon along with the Cr₂O₃. Prepared NFC has been used as bitumen modifier and the blending of NFC with bitumen were done using both conventional and microwave heating methods to study the proper blending methods to enhance the bitumen properties. Thermogram of the modified bitumen showed that the decomposition temperature increases by increasing the percentage of NFC (5-25%) in both the heating methods, but comparatively the thermal stability is more in microwave mixing than in conventional mixing. The morphology analysis of the modified bitumen showed that non-uniform blending in conventional type of heating and homogeneously blended mixture in microwave type of heating. The penetration value and ductility decreases while softening point and kinematic viscosity increases by increasing the quantity of NFC from 5 to 25% in modified bitumen. Microwave heat mixing method yielded better modified bitumen with NFC than conventional heating method in terms of stability, uniform blending and physical properties. The non-leachability of the Cr(III) in the NFC modified bitumen was confirmed through total chromium analysis in the leachate. But, chromium analysis in leachate of NFC immersed in acetate buffer for one month showed leaching of Cr(III) 5.5 μg/L in the 25% NFC modified bitumen block mixed using conventional heating method.