Technician Training and Certification Program January 2003

{PAGE }

Resistance to Plastic Flow of Bituminous Mixtures Using Marshall Apparatus AASHTO T-245-97 (2001)

(Modified) This method covers the measurement of the resistance to plastic flow of cylindrical specimens of bituminous paving mixture loaded on the lateral surface by means of the Marshal apparatus. The results from this test may be used to compare the ratio of stability to flow. Stability to flow ratios 200 and above, to some extent, indicate a mix that may be rut resistant, while values below 200 could be prone to rutting and a tender mix.

Modifications: 1. The temperature of the mold assembly should be maintained at the molding temperature shown on the mix design ± 2° C (3.6ºF), not the temperature shown in AASHTO.

2. Temperature of the mix sample should be brought to the mixing temperature ± 2° C (3.6ºF) as shown on the mix design, not the molding temperature.

3. Any method of maintaining the temperature of the testing head may be used and shall not be limited to a water bath.

4. The compacted specimen shall be stabilized in the mold for 10 to 20 minutes before extruding in order to prevent distortion.

5. A mechanically operated hammer shall be used. Key Elements:

Molding of Briquettes

1. Obtain sample. Obtain sample in accordance with T-168 (Modified). The sample shall be of sufficient size to prepare at least four (4) specimens. Three specimens shall be molded and the average results shall be determined from those three specimens. If a briquette is damaged, the additional material will be used to mold a new third briquette.

Note: The intent of this test procedure is that the first three molded briquettes be

used in determination of results. It is not the intent of this test that all four briquettes are molded and the three closest results be used, or all four briquettes be used to determine the average.

2. Inspect, adjust, and calibrate apparatus. Mold assemblies (2.1) and the compaction hammer

(2.3) need to be thoroughly cleaned. The mechanical hammer used for compaction must be adjusted to give results comparable with the calibrated hand hammer (Note 2). To be considered comparable, the average bulk density of three (3) hand compacted specimens and three (3) mechanically compacted specimens must be within 0.010 or less.

3. Heat mold assemblies, hammer and hand tools. Heat the mold assemblies to the molding

temperature shown on the mix design ± 2°C (3.6ºF). The compaction hammer shall be heated to between 93.3°C and 148.9°C (200-300ºF). All hand tools shall be heated during use. The mold assembly and face of the compaction hammer shall be thoroughly cleaned (3.5.1).

Technician Training and Certification Program January 2003

{PAGE }

AASHTO T-245, Continued…

4. Bring sample to mixing temperature. The sample can be brought to the mixing temperature shown on the mix design ± 2°C (3.6ºF). Heating of the mix in the mold will not be allowed at any time .

5. Place mix in mold. Place a paper filter in bottom of the mold and add the entire batch of heated

material to the mold in one lift. Spade the material vigorously with a heated spatula 15 times around the perimeter and 10 times over the interior. Smooth the surface to a slightly rounded shape, place a filter paper on top of mixture; place in compaction device (3.5.1).

6. Compact material. Immediately prior to compaction verify that the temperature of the mixture

in the mold is within ± 2°C (3.6ºF) of the molding temperature shown on the mix design. Unless otherwise noted, apply 75 blows with the compaction hammer. Reverse and reassemble mold and apply appropriate number of blows to second side as quickly as possible to prevent loss of heat (3.5.2).

7. Extract specimen from mold. Let the specimen stabilize for 10 to 20 minutes in the mold, then

using an appropriate specimen extractor extract specimen from mold while it is still warm. 8. Cure specimen. Once specimen is removed from mold, place the specimen on a smooth, flat

surface and allow specimen to stand overnight at room temperature (3.5.2). Stability and Flow

1. Weigh specimen. Remove any loose material and weigh for testing by AASHTO T-166. 2. Measure height of each specimen. Measure specimen height to nearest 1.6 mm (1/16 in.).

Record height. 3. Immerse in water bath. Bring specimens to specified temperature by placing in a water bath

maintained at 60 ± 1°C (140 ± 1.8ºF) for 30 to 40 minutes (4.1). 4. Prepare compression testing machine, breaking head, and flow meter. Thoroughly clean

guide rods and inside surfaces of the breaking head, and lubricate guide rods so that the upper test head will slide smoothly over them. Maintain testing head temperature between 21.1°C and 37.8°C (70-100ºF) (4.1). Zero flow meter using dry, unbroken briquette. Inspect compression testing machine, ring dynamometer assembly and micrometer dial (2.8).

5. Place specimen in breaking head and place on testing machine. Remove specimen from

water bath and place in lower portion of breaking head, place upper portion of breaking head on specimen, position assembly in testing machine. Place flow meter over longer guide rod and verify zero on dial (4.1).

6. Apply load. Hold flow meter firmly against the upper segment of the breaking head while

applying load (4.1). Apply load at a constant rate of 50.8 mm (2 in.) per minute, until maximum

Technician Training and Certification Program January 2003

{PAGE }

AASHTO T-245, Continued…

load is noted on micrometer dial. Immediately remove flow meter. Complete steps 5 and 6 within 30 seconds (4.2).

7. Record flow and maximum load. 8. Compute results. Using the current calibration chart for the compression-testing machine,

calculate stability for each specimen. If height of the specimen is other than 63.5 mm (2.5 in.), as measured in step No. 2, correct in accordance with Table 2, Stability Correlation Ratio Chart. (5.1.2). Calculate the stability/flow ratio.

9. Report results. The stability test result is reported as the average load of three specimens

recorded to the whole number (5.1.2). The flow is the average of the three specimens recorded in hundreds of an inch (5.1.3).