2.3.2. Rheological Performance Tests

(1) DSR Test

A dynamic shear rheometer (DSR) with parallel plate geometry was applied to study the rheological behavior of asphalt binder at high and intermediate temperatures according to ASTM D 7175 [39]. Plates of a 25 mm diameter spaced 1 mm apart were selected for samples to detect the shear storage modulus G and shear loss modulus G at high temperatures. The linear viscoelastic range of each sample was identified by a strain sweep test. Each test was repeated twice to confirm a good repeatability of the data.

The frequency sweep test was carried out from 0.1 rad/s to 100 rad/s at 60 ◦C to obtain dynamic shear moduli. The temperature sweep test was performed at a fixed frequency of 10 rad/s and the temperature was raised from 30 ◦C to 90 ◦C with an interval of 5 ◦C to

evaluate the high-temperature performance. Samples aged in the rolling thin film oven test (RTFOT) and pressure aging vessel (PAV) were subject to a temperature sweep test from 10 ◦C to 40 ◦C to investigate the fatigue performance.

(2) MSCR test

The multiple stress creep and recovery (MSCR) test, according to ASTM D 7405 [40], was performed to obtain the non-recoverable creep compliance and percent recovery, which could accurately reflect the mechanical response of the polymer modified asphalt binder. The test was conducted at 60 ◦C by applying shear stresses of 0.1 kPa and 3.2 kPa, respectively. The RTFOT aged samples were applied in this experiment.

(3) BBR test

The bending beam rheometer (BBR) test was employed to measure the low-temperature rheological performance of asphalt binder, according to ASTM D6648 [41]. Two main factors, creep stiffness (S) and creep rate (m-value), which indicate the low-temperature crack resistance, were obtained under a 60 s loading. The stiffness is the ratio of stress to the total strain under a certain duration and temperature. The m-value reflects the relaxation rate of asphalt binders. RTFOT-PAV aged samples were characterized at −6 ◦C, −12 ◦C and −18 ◦C, respectively.

## 2.3.3. Storage Test

The storage stability test was conducted to identify the phase separation degree between polymer and asphalt binder. According to ASTM D7173 [42], approximately 50 g of compound modified binder were poured into a cigar tube with a diameter and height of 2.5 cm and 14 cm, respectively. Then, the tube was sealed and placed vertically in an oven at 163 ◦C. After storage for 48 h, the tube was taken out of the oven and put into the refrigerator to cool down. The cooled tube was divided into three equal parts and the softening points of the upper and lower parts were tested.
