AASHTO TP 70:2012 Standard Method of Test for Multiple Stress Creep Recovery (MSCR) Test of Asphalt Binder Using a Dynamic Shear Rheometer (DSR).
4. SUMMARY OF TEST METHOD
4.1. This test method is used to determine the presence of elastic response in an asphalt binder under shear creep and recovery at two stress levels at a specified temperature. For performance-graded (PG) asphalt binders, the specified temperature will typically be the PG high temperature from MP 19, Table 1.
4.2. Asphalt binder is first conditioned using T 240 (RTFOT). A sample of the RTFO-conditioncd asphalt is tested using T 315 (DSR). The 25-mm parallel plate geometry is used with a I-mm gap setting. The sample is tested in creep at two stress levels followed by recovery at each stress level. The stress levels used arc 0.1 kPa and 3.2 kPa. The creep portion of the test lasts for 1 s, which is ftllowed by a 9-s recovery. Ten creep and recovery cycles are tested at each stress level.
5. SIGNIFICANCE AND USE
5.1. This method is designed to identify the presence of elastic response in a binder and the change in elastic response at two different stress levels while being subjected to ten cycles of creep stress and recovery. Nonrecoverable creep compliance has been shown to be an indicator of the resistance of an asphalt binder to permanent deformation under repeated load.
6.1. Use the apparatus as specified in T 315.
7.1. conditioning—Condition the asphalt binder in accordance with T 240 (RTFOT).
7.2. Sample preparation—The sample for the MSCR test is prepared the same as samples for T 315 using 25-mm plates. The temperature control will also follow the T 315 requirements.
7.2.1. This test may be performed on the same sample that was previously used to determine the DSR properties of the RTFO residue as specified in M 320. When using the previously tested sample to perform this test, a I -mm relaxation period between the tests is required before running this test. When using a new sample to perform this test, the 1-minute relaxation period is not required.
7.3. Test protocol—The test is performed at the selected temperature using a constant stress creep of
1.0-s duration followed by a zero stress recovery of 9.0-s duration. The test is performed at IWO stress levels, 0.1 kPa and 3.2 kPa. Ten cycles are run at each of the two stress levels for a total of 20 cycles. The commanded full stress for each creep cycle shall be achieved within 0.03 s from the start of the creep cycle as certified by the equipment manufacturer. The stress and strain shall he recorded at least every 0.1 s for the creep cycle and at least every 0.45 s for the recovery cycle on an accumulated basis such that, in addition to other data points, the data points at 1.0 s and 10.0 s for each cycle’s local time are explicitly recorded. If the DSR does not record the strain at exactly 1.00 and 10.00 s, then the software shall extrapolate prior data to determine the strain value at
1.00 s and 10.00 s. Extrapolated data shall include a measured data point no more than 0.05 s prior to the required time for a creep cycle and no more than 0.30 s prior to the required time for a recovery cycle. There are no rest periods between creep and recovery cycles or changes in stress level. The total time required to complete the two-step creep and recovery test is 200 s.AASHTO TP 70 pdf download.