AASHTO R 92:2018 Standard Practice for Evaluating the Elastic Behavior of Asphalt Binders Using the Multiple Stress Creep Recovery (MSCR) Test

AASHTO R 92:2018. Standard Practice for Evaluating the Elastic Behavior of Asphalt Binders Using the Multiple Stress Creep Recovery (MSCR) Test.
3. TERMINOLOGY
3.1. Definitions:
3.1.1. Definitions of terms used in this practice may be found in ASTM D 8. determined from common
English usage, or combinations of both.
3.2. Definitions of Terms Specific to This Standard:
3.2.1. creep and recovery standard rheological test protocol whereby a specimen is subjected to a constant load for a fixed time period and then allowed to recover at a constant zero load for a fixed time period.
3.2.2. non-recoverable creep compliance (J,)—the residual strain in a specimen after a creep and recovery cycle divided by the stress applied.
3.2.3. Average percent recovery (R)—the ratio of the difference between the peak strain and the residual strain to the peak strain, expressed as a percentage. This is a measure of the elastic response of an asphalt binder at a given temperature and applied stress level.
4. SUMMARY OF PRACTICE
4.1. This practice is used to evaluate the elastic response of an asphalt binder under shear creep and recovery at a specified temperature. For most asphalt binders, this temperature will be the high temperature grade as determined only by environmental conditions (not as adjusted for traffic speed or loading).
4.2. Asphalt binder is first aged in accordance with T 240 (RTFOT). A sample of the RTFO-aged asphalt is tested in accordance with T 350 (MSCR). Unless otherwise specified. the 25-mm parallel plate geometry is used with a 1-mm gap setting. The sample is tested in creep and recovery at two stress levels. The stress levels used are 0. I kPa and 3.2 kPa. The creep portion of the test lasts for one second which is followed by a nine-second recovery. Ten creep and recovery conditioning cycles are first conducted at a shear stress of 0.1 kPa. The test is then executed by conducting ten creep-recovery cycles at each shear stress level (0.1 and 3.2 kPa). Two parameters are derived from the MSCR test: the non-recoverable creep compliance (J.) and percent recovery
(R).
4.3. Using the Jnr and R values from testing conducted at 3.2 kPa shear stress (identified as Jnr3.2 and R-3.2. respectively) data is compared to a curve of R as a function Ofinr. Values that plot on or above the curve are considered to represent an asphalt binder with a significant elastic response indicative of modification using clastorneric polymers.AASHTO R 92 pdf download.