AASHTO TP 78:09(2013) Standard Specification for Detecting the Presence of Phosphorous in Asphalt Binder.
Note 1—One agency found that the cans they were using for this test had been lubricated during the manufacturing process with a lubricant containing phosphates. This resulted in a positive result in this test even with the empty can. If there is doubt about the condition of the containers being used, then take the precaution of running a blank test with no asphalt.
7.1. Sample the material in accordance with R 66. Sec Note 2 regarding potential concerns regarding contamination of sampling container.
8.1. 1 leat the asphalt and pour 1 to 2 g into a I -oz can or other small container.
8.2. Place the container in an oven set at 163 ± 10°C for 10 mm to ensure the asphalt is fluid.
8.3. Remove the container, arid immediately add 2 mL of butyl alcohol while stirring the container.
8.4. Continue to stir the container and add 2 mL of distilled water.
8.5. While still stirring the container, add 2 mL of the ascorbic acid color reagent. After the addition of the color reagent, stop stirring and allow the sample to sit for 5 to 10 mm.
8.6. If phosphoric acid is present in the asphalt. a blue color will develop within 5 to 10 mm. Decant the solution into a second container if unable to see the color.
Note 2 —After 30 mm. the results arc not reliable. The color may either fade or intensify after 30 miii.
8.7. If a blue color appears, the sample is reported as ‘positive.” The sample is reported as negative” if it does not turn blue.
Note 3—The blue color, if present, will be in the aqueous phase, which will be at the bottom. Often the top layer has a brown or green color.
8.8. When new reagents are prepared, prepare and run a blank (asphalt with no phosphoric acid).
9. 1. This report shall include the following:
9.1.1. Identification of sample.
9.1.2. “Positive” or “Negative” result.
10.1. Precision— -The research required to develop precision estimates has not been conducted.
10.2. Bias—This test method has no bias since the values determined can only be defined in terms of this test method.
11 .1. Asphalt; phosphoric acid; PPA.AASHTO TP 78 pdf download.