INTERNAL STRUCTURE ANALYSIS OF ASPHALT MIXES TO IMPROVE THE SIMULATION
OF SUPERPAVE GYRATORY COMPACTION TO FIELD CONDITIONS
Laith Tashman, Eyad Masad, Bob Peterson, Habeeb Saleh
ABSTRACT
The laboratory compaction method influences the design and performance testing of asphalt mixes. For a
performance test to yield reliable mechanical properties, it is necessary to ensure that laboratory specimens
are fabricated in a manner that adequately simulates field compaction. The simulation is based on the
distribution of aggregates and air voids inside the mix, which is referred to in this study as the internal
structure.
This study evaluated the ability of the Superpave gyratory compactor (SGC) to simulate the internal
structure of asphalt pavements, and the influence of different field compaction patterns on the produced
internal structure. Computer automated image analysis techniques and X-ray computed tomography were
used to capture and quantify the internal structure distribution.
Three field test sections were constructed using different compaction patterns. SGC specimens were
prepared using different values for the angle of gyration, applied pressure, specimen height, and
temperature of base plates and mold in order to determine the best combination of gyratory internal
variables that would simulate field compaction. In addition, the study evaluated the sensitivity of the
compaction curve characteristics to changes in the SGC variables.
The results indicated that the different field compaction patterns used in this study produced similar
internal structure in asphalt pavements. However, changing the compaction variables in the SGC (angle,
pressure, height, and temperature) influenced the internal structure in laboratory specimens. It was possible
to simulate the internal structure of asphalt pavements by changing the angle of gyration and specimen
height in the SGC. Increasing the temperature of base plates and mold of the gyratory compactor assisted in
developing more random distribution of air voids within a specimen.
The influence of improving the simulation of SGC specimens to asphalt pavement internal structure on
performance testing was evaluated by measuring the stiffness of field cores and SGC specimens using the
shear frequency sweep test. The performance testing results supported in most part the findings of the
internal structure analysis. Improving the simulation of asphalt pavement in SGC specimens reduced the
difference in stiffness between SGC specimens and field cores.