SULPHUR ASPHALT PELLET
PERFORMANCE IN THE
ASPHALT PAVEMENT ANALYZER

SCOPE:

Two forms of sulphur/asphalt pellets were evaluated for performance in the Asphalt Pavement Analyzer (APA).  Performance was measured in terms of resistance to rutting, resistance to fatigue failure, and resistance to moisture damage. A 4.75 mm asphalt mix was used to prepare test specimen with each of the two forms of sulphur pellets.  In addition control specimens were prepared with PG67-22 asphalt cement.

SULPHUR PELLETS:

Sulphur Extended Asphalt Modifier (SEAM) was one of the pellet forms and the other was Asphalt Replacement Pellets (ARP).  The Specific gravity of SEAM was determined to be 1.927 and accompanying literature suggested it should be substituted for 30 to 50% of the asphalt cement.  ARP specific gravity was determined to be 1.619 and it is a total replacement for asphalt.  Melting point was determined to be 240 to 250 degrees F for these products.

MIX DESIGN:

The 4.75mm maximum nominal size mix design used in this study represented quarry crushed aggregate with all faces crushed.  Characteristics of the design are in table 1.

Mix Design Characteristics
Table 1

SPECIMENS PREPARATION:

The control specimens were prepared by adding the asphalt cement at 320 degrees F to the aggregate at 350 degrees F and mixing until the aggregate was well coated.  This required 30 - 40 seconds.

Test specimens were prepared with 45% of the asphalt cement replaced with SEAM.  The weight percentage of asphalt cement was 3.19% (0.55 x 5.8 = 3.19), and 4.91% SEAM by weight was used (5.8 x 0.45 x 1.927 +1.025 = 4.91%).  Asphalt cement at 320 degrees F was added to the aggregate at 350 degrees F and the mixing began prior to adding the SEAM at room temperature. Coating the aggregate required 60 - 70 seconds.

Test specimens were prepared using ARP.  The weight percentage was adjusted to 9.16% (5.8 x 1.619 + 1.025 = 9.16, where the 1.025 is the approximate specific gravity of the asphalt cement).  The ARP was added at room temperature to aggregate at 350 degrees F and mixed until the aggregate was well coated.  This required 100 to 120 seconds.  The resulting mixture had little cohesive character.  In a second attempt the aggregate was heated to 325 degrees F.  Cohesion of this mix was much improved.

AGING AND COMPACTING:

All specimens were short term aged for two hours at 300 degrees F in accordance with Superpave procedures, and immediately compacted to a targeted 7 +/- 1% air voids in the Asphalt Vibratory Compactor (AVC).

Specimens prepared for testing resistance to fatigue failure were compacted then aged in an oven at 185 degrees F (85 degrees C) for five (5) days prior to testing.

RUT TESTING:

Test specimens and control specimens were heated to 64 degrees C (147 degrees F) in the APA test chamber and tested for resistance to rutting in accordance with the test method.  Results are in Table 2.

Rut Depth mm
Table 2

SEAM was 6 times more resistant to rutting than the control while ARP was more than 11 times more resistant that the control specimens.  SEAM can be substituted for 30 to 50% of the asphalt cement.  Forty-five percent (45%) SEAM was substituted in these test specimens; therefore the heavy dosage produced the high resistance to rutting.

FATIGUE RESISTANCE:

The test specimens and control specimens were cooled to 20 degrees C (68 degrees F) in the APA and tested for resistance to fatigue in accordance with the test method.  Results are in Table 3.

Fatigue Resistance Cycles to Failure
Table 3

All testing was done by Mr. Ron Collins of  Pavement Technologies Inc.
Covington, Georgia (770) 388-0909 ....thank you Sir Ron.