The rheological properties and fracture properties of asphalt are key indicators for evaluating its application in road engineering. The dynamic shear rheometer method is used to determine the dynamic shear modulus and phase angle of asphalt to analyze its rheological properties at different temperatures and frequencies. The direct tensile method, on the other hand, is used to evaluate the fracture properties of asphalt, including failure strain and stress. Through these two test methods, it can provide an important scientific basis for the performance classification and application of asphalt materials, and ensure its reliability and safety in practical use.
The study of the rheological properties of asphalt as an important road material is essential to understand its performance under different temperature and stress conditions. In this paper, we will discuss the rheological properties of asphalt in detail, focusing on the dynamic shear rheometer (DSR) method and the direct tensile method, and analyze their purpose, scope of application, instrument requirements, method steps and the report of experimental results.
Dynamic shear rheometer method
Purpose and Scope of Application
The dynamic shear rheometer method is designed to determine the dynamic shear modulus (G*) and phase angle (δ) of asphalt. This method is suitable for many types of asphalt, including as-is asphalt, pressure-aged asphalt, and membrane oven-aged asphalt. The dynamic shear modulus is measured in a range of 0.1 to 10 MPa and is suitable for temperatures ranging from 5 to 85 °C. It should be noted that this method is only suitable for bitumen with a particle size of less than 250 μm.
Instrument and material technical requirements
Breadboard – Use two sizes of metal plates, 8mm and 25mm in diameter, with a smooth surface.
Environmental chamber – used to control the temperature of the specimen during the test to ensure that the heating or cooling medium does not affect the bitumen properties.
Temperature controller – capable of controlling the specimen temperature within ±0.1°C from 5 to 85°C.
Loading equipment – should be able to apply sinusoidal oscillating loads of 10 rad/s ± 0.1 rad/s.
Data Acquisition System – Records temperature, frequency, deflection angle and torque to meet accuracy requirements.
Methods and Steps:
Specimen preparation
1. Prepare the sample according to the T0602 standard, heat the asphalt to a flowing state, the heating temperature of the original asphalt does not exceed 135 °C, and the modified asphalt does not exceed 163 °C.
2. Fix the breadplate on the rheometer and make sure that the test gap is 1mm±0.05mm or 2mm±0.05mm, depending on the diameter of the specimen.
3. Clean the surface of the breadboard to ensure that the asphalt adheres evenly to the breadboard.
Test procedure
1. Adjust the temperature of the test specimen to ±0.1°C, and start the test after 10 minutes.
2. Test under stress or strain control, and select the appropriate stress or strain value according to different control methods.
3. Record the data and calculate the composite shear modulus and phase angle.
Reporting & Errors
The test report should include information such as breadboard diameter, test clearance, test temperature, frequency, stress or strain, composite modulus, and phase angle. At the same time, the name, specification and instrument model of the experimental material should be recorded. Errors in repeatability and reproducibility test results should be in accordance with the specified standards.
Direct stretch method
Purpose and Scope of Application
The direct tensile method is used to determine the failure strain and failure stress of asphalt, which is suitable for the original asphalt and the asphalt after aging treatment, and the test temperature range is 0~-36 °C. This method is also only suitable for bitumen with a particle size of less than 250 μm.
Instrument and material technical requirements
Closed-circuit coupled feedback control of displacement and loading systems
Specimen clamping system – ensures stability in a cold bath.
Cryogenic liquid cold bath – temperature controlled range to test temperature ± 0.1°C.
Load and elongation measurement systems – accuracy requirements of 0.1 N and 1 μm respectively.
Methods and Steps:
Specimen preparation
1. Prepare the sample according to the T0602 standard, and heat the asphalt to a flowing state, not exceeding 135 °C (modified asphalt not exceeding 165 °C).
2. Use a release agent to coat the inside of the test mold to ensure uniform coating and prevent asphalt from sticking.
Test procedure
1. Set the cold bath at the test temperature and stabilize within the range of ±0.1°C.
2. Pour the asphalt sample into the mold and allow it to cool and solidify.
3. Put the specimen into the direct tensile Tester, apply the tensile load, and record the failure strain and stress.
Reports & Considerations
The test report should detail the test conditions, the materials used and their sources, and provide data on the results of the experiment. Care should be taken to ensure that the specimen preparation and testing process is carried out within the specified temperature and time range to ensure the reliability of the results.
summary
The rheological properties and fracture properties of asphalt are important evaluation criteria for its application in road engineering. The dynamic shear rheometer method can be used to effectively analyze the rheological properties of asphalt at different temperatures and frequencies, while the direct tensile method is used to measure its fracture properties. These two test methods complement each other, provide a scientific basis for the performance classification and practical application of asphalt materials, and ensure the reliability and safety of the project. A better understanding of these properties allows for better optimization of asphalt formulation and application processes, thereby improving the service life and performance of the road.
