SHRP-A-379 traducir

could interfere. If the absorbance values of the blank are greater than 0.010 for any of
the readings, this absorbance value must be subtracted from all absorbance readings
taken with that aggregate (A, and At).
8.6 Stopper the flasks with a #10 neoprene stopper, and place each flask securely in
the holder atop the shaker apparatus.
8.7 Turn on the shaker and adjust the speed to approximately 300 rpm. The rate
should be high enough to insure good mixing, but without danger of throwing the flasks off
the table. Once the appropriate table speed is determined for the particular shaker, this same
speed should be used for all tests run in the laboratory.
8.8 Record the starting time on the data sheet and/or laboratory notebook.
8.9 Using the micropipettor, transfer 4.00 mL of the stock asphalt cement solutions
for each asphalt cement being tested into a clean, dry 25 mL volumetric flask, and dilute to
the mark with fresh toluene. Holding the stopper on the flask with the fingers, invert the
flask at least 6 times to mix the solution.
8.10 Transfer about 4 mL of the diluted stock solution into a spectrophotometer
cuvette, and determine the absorbance at 410 nm in the spectrometer. Record this value on
the data sheet and/or laboratory notebook as "initial absorbance," or Ai.
8.11 Using the ring stand and appropriate clamps, set up a funnel for each sample,
with a clean, dry spectrophotometer cuvette under each funnel stem. Place a piece of folded
filter paper in each funnel.
8.12 After 6.0 hours, stop the shaker table, allow the solution to settle for
10 minutes. Using the adjustable pipettor, transfer 4.00 mL of each solution to an
appropriately marked clean, dry 25-mL volumetric flask. Dilute to the mark with clean
toluene, stopper, and mix thoroughly by inverting the volumetric flask a minimum of six
times while holding the stopper on with the fingers.
8.13 Carefully pour sufficient contents of the 25-mL volumetric flasks into the funnel
to filter at least 4 mL of solution into each of the cuvettes.
8.14 Measure the absorbance of each cuvette at 410 nm in the spectrometer. Record
this value on the data sheet and/or laboratory notebook under the heading "Abs. @ 6.0 hrs"
or Aa.
8.15 Using the adjustable micropipettor, transfer 2.00 mL of water to each of the
500 mL Erlenmeyer flasks on the shaker table, replace the neoprene stoppers, and restart the
shaker. Note the time on the data sheet and/or laboratory notebook. The shaker will now be
allowed to run overnight while the water desorption step takes place.
91