Asphalt Extraction Essay

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Extraction of Asphalt from a mix is a common practice in the asphalt laboratories. The extracted asphalt is used for characterization in the laboratories to ensure quality, performance and research. ASTM D2172 is the most accepted procedure for asphalt extraction. This procedure includes five methods such as Method A the centrifuge extraction, Method B the Reflux extraction, Method C first variation of the Reflux method, Method D the second variation of Reflux method and Method E the vacuum extraction. Among them centrifuge method is most popular because the asphalt extracted using Reflux method is subjected to more aging and the vacuum extraction method is not used in a regular basis. There are other methods which are as follows Determination of asphalt binder content from asphalt mixtures using the Asphalt Nuclear Gauge and Determination of Asphalt binder content of Hot Mix Asphalt (HMA) by ignition method. However, in this paper the discussed methods will be limited within chemical based extraction method. Extracted asphalt has to be recovered from the solution. The methods used for recovery are ASTM D1856, Recovery of Asphalt from Solution by Abson method and ASTM D5404, Recovery of Asphalt using Rotovapor apparatus. The solvents used for recovery are trichloroethylene, methylene chloride, 1, 1, 1-trichloroethane, and nitration based benzene etc. Among them benzene is the most toxic solvent. The properties obtained from these test methods were erroneous so it was necessary to develop new methods. Strategic Highway Research Program (SHRP) developed modified extraction and recovery procedures to compensate those errors. The SHRP extraction procedure (AASHTO TP2) is more precise as it uses rotating cylinder with baffled inside wh...

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...ew chlorinated solvent creates severe aging such as Carbon tetrachloride, 1, 1, 1-trichloroethane etc. Age hardening occurs in almost all the solvents but weaker the solvent i.e. toluene lower the hardening (4). A vacuum extraction cylinder is used to remove the extract from the cylinder. In this procedure, the method for recovery is a modification of Rotovapor method. To remove the asphalt from the mix about seven wash of solvent is necessary (1). There are few problems using SHRP method. This method recovers only 50g of sample which is enough for one test like Dynamic Shear Rheometer (DSR). Several extraction and recoveries would be necessary in order to run some more tests e.g. Pressure Aging Vessel (PAV) and Bending Beam Rheometer (BBR). Each extraction and recovery requires six hours and has to be operated carefully to avoid the incidence of flash boiling (2).

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