Developed during SHRP as principal laboratory compaction equipment for asphalt mixture design. Operates using 1.25-degree angle of gyration with 600 kPa vertical pressure. Rotational speed is 30 gyrations per minute. Generally follows French gyratory compaction procedure, which was originally a modified version of the Texas gyratory compaction procedure. Continuous height recordation allows for real-time monitoring of density. May also have some value in estimating the shear resistance of asphalt mixtures.
Marshall Compaction, 4” Diam., set of 3 specimens (AASHTO T245)
Developed in the 1940's by Bruce Marshall ( Mississippi ) as a modified form of the soil test (proctor). Impact compaction generated by 10-pound sliding weight hammer. Not used in Superpave mix design because: (a) standard procedure for 4” (100 mm) diameter specimens did not permit mixtures with larger aggregate sizes (i.e. 25 mm); (b) modified procedure for 6” (150 mm) diameter specimens resulted in crushing of aggregates; (c) impact compaction was found to be least representative of actual field compaction (through mechanical property testing and analysis); (d) highest compaction level still did not adequately account for high traffic pavements; and (e) monitoring of density during compaction was not available. Also includes stability and flow analysis of asphalt mixtures.
Maximum Theoretical Specific Gravity (AASHTO T209, ASTM D2041)
Used in conjunction with the bulk specific gravity, this method determines the percentage of air voids at various asphalt contents. Controlling air void percentage is an important element in both the Marshall and Superpave mix design systems.
Centrifuge Extraction (AASHTO T164, ASTM D2172)
A component analysis test. The centrifuge extraction is used to determine asphalt cement and aggregate content. The extracted asphalt can be recovered and tested and the aggregate can evaluated to confirm specified requirements.
Centrifuge Extraction with Rotavapor Recovery (ASTM D2172 and ASTM D5404)
Once the hot mix components are separated, further analysis can be performed. The rotavapor recovery ‘recovers' the asphalt binder for further testing. The effluent is rotated in a flask under heat and vacuum to remove solvents from the extraction process leaving the only the binder.
Included tests:
Gradation of extracted aggregate
SHRP Extraction/Recovery
Using a different extraction procedure, the recovery phase of this method is similar to the roravapor but uses lower temperature to avoid overheating sample and higher vacuum.
Marshall Mix Design
Was the principle method of mix design prior to Superpave.
Superpave Mix Design
This system is an improvement on the marshall mix design system. The gyratory compactor is used instead of the marshall hammer and aggregate properties testing plays more of a role.
