The acid number and flexural creep properties of bitumen are key indicators to evaluate its material properties. The acid number reflects the chemical stability of the asphalt and affects its aging resistance, while the bending creep properties reveal the deformation ability of the asphalt under long-term loading. Through reasonable testing and analysis, these parameters can effectively guide the application and optimization of asphalt in road engineering, and improve the service life and performance of materials. Asphalt is an important road material, and its properties play a vital role in the service life and quality of the road. In order to accurately understand the properties of bitumen, commonly used testing methods include acid number determination and flexural creep stiffness testing.
Methods for determining the acid number of asphalt
Purpose and Scope of Application
Asphalt acid number is an important indicator used to measure the free acid content in asphalt. This method is suitable for the determination of the acid number of road petroleum asphalt, and its principle is to dissolve the free acid in the asphalt by mixing a solvent of benzene and ethanol, and then neutralize the acid with a standard solution of potassium hydroxide ethanol to calculate the consumption of potassium hydroxide to determine the acid value.
Instruments & Materials
Required instruments and materials include potassium hydroxide ethanol standard solution, absolute ethanol, benzene, round-bottom flask, spherical reflux condenser, Thermostatic Water Bath, glass electrode, saturated calomel electrode, etc. Potassium hydroxide ethanol standard solutions need to be prepared and calibrated according to conventional methods of inorganic chemistry.
Test Steps
Sample Preparation – Take a certain amount of bitumen sample (3-5g) and place it in a 250mL round-bottom flask.
Dissolve the bitumen – add 15-25 mL of benzene and reflux the flask in a constant temperature bath at 65 °C for 0.5 hours to dissolve the bitumen.
Stand & Titrate—Add 100 mL of absolute ethanol and let the flask seal overnight. Subsequently, titration is carried out with a potassium hydroxide ethanol standard solution by potentiometric titration until the titration endpoint is reached.
Blank test – A blank sample is prepared in the same way and the volume of potassium hydroxide ethanol standard solution consumed is determined.
Result calculation
The formula for calculating the bituminous acid number is based on the volume of potassium hydroxide solution consumed during the titration. By comparing the results of the titration of the blank specimen and the sample to be tested, the acid number of the bitumen can be accurately calculated.
Methodological review
This method has certain similarity with other methods for detecting the acid value of oils (such as GB 264 lubricating oil acid value test, GB5530 vegetable oil acid value determination method), and the operation steps are simple and the measurement results are accurate, which is one of the commonly used methods in asphalt acid number testing.
Asphalt bending creep stiffness test
Purpose and Scope of Application
The flexural creep stiffness test is an important means to evaluate the deformation resistance of asphalt at low temperatures. The measurement of bending creep stiffness and m value of asphalt by bending beam rheometer can provide an important reference for the low-temperature crack resistance of asphalt. This method is suitable for asphalt samples after unaging, pressure aging and rotary film oven aging, and the measured flexural stiffness range is 20~1000MPa.
Instruments & Materials
The test system is mainly composed of the following parts: loading frame, constant temperature bath, computer control system, sample beam mold, correction system, etc. The loading system is capable of applying a contact load of 35 mN and increasing to 980 mN in 0.5-5 seconds. The temperature of the thermostatic bath is accurate to ±0.1°C, ensuring that the temperature remains constant during the test.
Test Steps
Preparation – Prior to the test, ensure that the software, loading and data acquisition systems are functioning properly, and that the temperature of the thermostatic bath is adjusted to the specified test temperature.
Loading Setup – Place the stainless steel beam on the bracket and adjust the loading system so that the initial contact load reaches 35mN and gradually increases to the test load of 980mN.
Specimen Preparation – Specimen preparation using an aluminum or stainless steel mold ensures that the specimen meets the required dimensions (length 127 mm, thickness 6.35 mm, width 12.7 mm).
Flexure test – the specimen is placed in a thermostatic bath, a test load is applied to the loading frame, and the load and deformation at different time points are recorded.
Analysis of results
In the test, the bending creep stiffness value and m value were calculated by recording the load and deformation data at 8s, 15s, 30s, 60s, 120s and 240s. If the deformation is too large or too small, the test results will be invalid. The test results can help predict whether cracks will occur in the actual use of asphalt due to low temperatures.
Methodological review
The flexural creep stiffness test method is an important method to evaluate the low-temperature performance of asphalt, and its accurate load control and temperature control system make the test data more reliable. Through this method, asphalt materials suitable for use in cold areas can be effectively screened.
summary
The acid number and bending creep properties of asphalt are crucial for its application in road engineering. The acid number mainly affects the aging resistance of asphalt, while the flexural creep properties reflect the deformation ability of the material under long-term loading. Through the evaluation of these key parameters, the asphalt formulation and construction process can be optimized, the durability and service life of the road can be improved, and the quality of the project can be stabilized.
