106.3.2.85 TM-85 Determination of Polyphosphoric Acid (PPA) in Performance Graded (PG) Asphalt Binders

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This test method determines the amount of PPA in PG grade asphalt binders by sodium carbonate fusion. PG grade asphalt binder is fused with sodium carbonate and dissolved in an acid solution. The solution is an analyzed on an Inductively Coupled Plasma Optical Emission Spectrophotometer (ICP-OES) as phosphorus and calculated as %PPA.

106.3.2.85.1 Equipment and Reagents

1. Inductively Coupled Plasma Optical Emission Spectrophotometer (ICP-OES) capable of internal standard correction (Varian Vista-MPX ICP-OES equipped with a Charged Coupled Device (CCD) Simultaneous detector) or comparable instrument.

2. Hydrochloric Acid (HCl), specific gravity 1.19.

3. Trace Metal Grade Nitric Acid solution (1:24).

4. Sodium carbonate (Na2CO3) Anhydrous, certified ACS powder.

5. Single Element Yttrium Standard- 1000 ug/ml

6. Single Element Phosphorus Standard – 1000 ug/ml

7. Platinum crucible, 25 ml capacity.

8. Borosilicate glass beaker, 400 ml.

9. Volumetric flask, 1000 ml.

10. Volumetric flask, 100 ml.

11. Adjustable Pipet (100 ul – 1000 ul)

12. Adjustable Pipet (20 ul – 100ul)

13. Balance with an accuracy of 0.1 mg.

106.3.2.85.2 Selection of Standards

If the procedure below is followed, a 0.50% addition of PPA to PG Grade Asphalt will result in a phosphorus concentration of 1.63 parts per million (ppm) in the final solution. Therefore, to bracket this concentration, phosphorus standards of 0.00 ppm, 0.50 ppm, 1.00 ppm, 2.50 ppm and 5.00 ppm were selected as the calibration standards for the ICP-OES instrumentation.

106.3.2.85.3 Preparation of Standard Solutions

1. Blank Solution – 0.00 ppm Phosphorus – pipet 400 ul of the 1000 ug/ml Yitrium standard into a 100 ml volumetric flask and bring to volume with the 1:24 Nitric Acid solution.

2. Standard 1 – 0.50 ppm Phosphorus - pipet 400 ul of the 1000 ug/ml Yitrium standard and 50 ul of the 1000 ug/ml Phosphorus standard into a 100 ml volumetric flask and bring to volume with the 1:24 Nitric Acid solution.

3. Standard 2 – 1.00 ppm Phosphorus - pipet 400 ul of the 1000 ug/ml Yitrium standard and 100 ul of the 1000 ug/ml Phosphorus standard into a 100 ml volumetric flask and bring to volume with the 1:24 Nitric Acid solution.

4. Standard 3 – 2.50 ppm Phosphorus - pipet 400 ul of the 1000 ug/ml Yitrium standard and 250 ul of the 1000 ug/ml Phosphorus standard into a 100 ml volumetric flask and bring to volume with the 1:24 Nitric Acid solution.

5. Standard 4 – 5.00 ppm Phosphorus - pipet 400 ul of the 1000 ug/ml Yitrium standard and 500 ul of the 1000 ug/ml Phosphorus standard into a 100 ml volumetric flask and bring to volume with the 1:24 Nitric Acid solution

106.3.2.85.4 Procedure

Heat PG grade asphalt binder sample in a 135° C oven until sample is sufficiently fluid to pour. Pour 1.0000 +/- 5 mg into a platinum crucible. Cool for a minimum of 15 minutes and transfer 5 grams of anhydrous sodium carbonate on top of the cooled sample. Run a blank concurrently with sample using same amount of sodium carbonate. Place cover over platinum crucible and place in a cool muffle furnace. Bring muffle furnace up to 1000° C and keep in furnace for a minimum of 30 minutes. After 30 minutes, using tongs, carefully take crucible with cover out of muffle furnace and set aside to cool. Place cool crucible plus cover into 400 ml beaker and add 75 ml of 1:3 HCl. When fused sample is completely dissolved, quantitatively transfer platinum crucible and cover out of beaker using a stirring rod and wash with deionized water. Add 4 ml of Yttrium to the 1000 ml volumetric flask and, quantitatively, transfer solution into the 1000 ml volumetric flask using deionized water. Dilute to volume and analyze on ICP-OES for phosphorus.

106.3.2.85.5 Calculation

Results from the ICP-OES will be in ppm phosphorus. To convert this result into %PPA added to the PG Grade Asphalt, the following conversion factor is applied:

0.316 x ppm Phosphorus from ICP-OES =  %PPA in PG Grade Asphalt