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9.4 Final Extraction and Recovery<br />
9.4.1 If the filtrate flowing through the transfer tube is a light brown color after a<br />
30-minute wash, proceed to the final recovery step.<br />
9.4.2 Pour contents of the current recovery flask into the original recovery flask.<br />
Attach the original recovery<br />
flask to the Rotavapor.<br />
9.4.3 Distill the contents of the recovery flask until it is about 1/afull.<br />
9.4.4 Disconnect the recovery flask and pour the contents into the centrifuge bottles.<br />
Fill the bottles so that their weights are equal. Wash any residue from the recovery flask into<br />
the centrifuge bottles. Raise the oil bath temperature to 177 + 2.5°C. Centrifuge the bottles<br />
at 3600 rpm for 25 minutes.<br />
9.4.5 Decant the asphalt-solvent solution into the recovery flask and add six 3-mm<br />
glass boiling beads. Attach the flask to the rotary evaporator. Disconnect the transfer tube<br />
from the rotary evaporator and replace it with the gas purge tube. Disconnect the filtrate<br />
transfer line from the external rotary evaporator neck fitting and replace it with the nitrogen<br />
gas line. Apply 700 mm Hg vacuum. Lower the flask 11/2in into the oil bath.<br />
9.4.6 Distill the solvent.<br />
9.4.7 When the condensation rate falls below 1 drop every 30 seconds, introduce<br />
nitrogen gas at 1000 mL/min. Maintain the gas flow, vacuum and bath temperature for<br />
30 + 1 minutes to reduce the residual solvent concentration to near zero. Complete removal<br />
of residual solvent is very important for obtaining accurate asphalt properties.<br />
9.4.8 Shut down the oil bath, flask rotation, vacuum, gas flow, and cooling water.<br />
Remove the evaporating flask and pour the asphalt into a sample tin.<br />
NOTE 6.--A high temperature annealing step is recommended as a finishing step. This enables the asphalt<br />
molecules to "realign" themselves and promotes the attainment of an equilibrium state. Flood the asphalt container<br />
with argon and cover. Heat container to 163°C and maintain temperature for 2 hours. Place container in a paint<br />
shaker for 5 minutes, and then allow to cool to room temperature.<br />
10. PRECISION AND BIAS<br />
10.1 Repeatability and reproducibility tests have not been established in accordance<br />
with standard AASHTO practice.<br />
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