Permanent deformation parameters for asphalt

The permanent deformation parameters for asphalt are determined from the Repeated Simple Shear Test at Constant Height (RRST-CH) in the laboratory.

Parameters determined from a number of calibration studies are shown in an Excel spreadsheet called ACPermanentDeformations.

The parameters in the spreadsheet are from the equations below:

For a number of materials in the spreadsheet the value of b was not determined from RSST-CH testing, as all testing was at a shear stress of approximately 70 kPa. Instead an assumed value (from previous experiments) of 1.03 was used. From those RSST-CH tests where b was determined it appears that the assumed value of 1.03 was too high. The values determined for DGAC range from 0.15 to 0.52. For modified binders the value was close to 0 (zero). For the materials with b equal to 1.03 it may be necessary to adjust the relationship to a lower b value before it is used in CalME.

The permanent deformation, in mm, is calculated from the permanent shear strain through:

where K is a calibration factor, determined through full scale testing.