As an important material widely used in road construction and maintenance, asphalt has a direct impact on the durability and service life of roads. Therefore, it is very important to accurately determine the density of asphalt mixtures. In this article, we will introduce two commonly used methods for measuring the density of asphalt mixtures: the water gravity method and the wax seal method.
Density test of compacted asphalt mixture (gravity in water)
Purpose and Scope of Application
The gravity in water method is mainly used to determine the apparent relative density or apparent density of the dense asphalt mixture specimen with a water absorption rate of less than 0.5%. Measurements are taken at a standard temperature of 25°C ± 0.5°C. When the specimen is very dense and there are almost no open pores that communicate with the outside world, the water gravity method can also be used to replace the traditional dry measurement method to calculate the volume indexes such as the porosity and the clearance ratio of the asphalt mixture.
Technical requirements for instruments and materials
Immersion balances or electronic balances – the maximum weight is less than 3kg, the inductance is not more than 0.1g, and when the maximum weight is more than 3kg, the inductance is not more than 0.5g.
Mesh basket – for hanging specimens.
Overflow tank – keeps the water level constant and is able to adjust the water temperature to within 25°C ±0.5°C.
Specimen suspension device - to ensure the safety of the specimen and the net basket suspension, the hanging wire should be made of non-absorbent materials.
Stopwatch, electric fan or oven – for recording time and speeding up drying.
Methods and Steps:
1. Select a suitable balance and weigh the aeromass (m₁) of the 1,000-dry specimen.
2. Put the specimen into a net basket, hang it in the water, adjust the water level, and weigh the mass in the water (m₂).
3. If the specimen is in a non-drying state, it needs to be dried to a constant weight with an electric fan or oven before weighing.
4. Calculate the apparent relative density and apparent density of the asphalt mixture specimen according to the formula, and calculate the relevant volume indexes, such as porosity, volume percentage of asphalt, etc.
report
The type of asphalt mixture and the method used to determine the density should be indicated in the test report. Due to its simplicity and convenience, the water gravity method has been widely used in the detection of asphalt mixtures with low water absorption.
Density test of compacted asphalt mixture (wax sealing method)
Purpose and Scope of Application
The wax sealing method is suitable for determining the gross volume relative density or gross volume density of asphalt concrete or asphalt gravel mixture specimens with water absorption greater than 2%. ±The measured relative density of gross volume can be used to calculate the volume index such as the porosity and the clearance ratio of the asphalt mixture.
Technical requirements for instruments and materials
Flood balances or electronic balances – for maximum weighing and sensitivity.
Baskets, Water Tanks – keep the water level constant and adjust the water temperature.
Paraffin – the melting point is known, and is used to seal the surface of the specimen.
Refrigerators, talcum powder, stopwatches, electric fans, electric stoves or gas stoves – for sample preparation and measurement.
Methods and Steps:
1. Weigh the airborne mass (m₁) of the dried specimen.
2. Cool the specimen to 4-5°C in the refrigerator and immerse it in molten paraffin until its surface is completely sealed.
3. Weigh the aerial mass (m₂) of the wax seal specimen, immerse it in the Water Tank, and read the water mass (m₃).
4. Use the corresponding formula to calculate the relative density of the gross volume of the specimen, and calculate the relevant volume index based on the data.
report
The type of asphalt mixture and the method used to determine the density should be recorded in detail in the test report. The wax sealing method is usually widely used in asphalt mixtures with high water absorption, but because of its complex method, the requirements for operators are high, and it needs to be carried out in strict accordance with the specifications.
conclusion
For the density determination of asphalt mixture, the water gravity method and the wax sealing method have their respective scope of application and advantages and disadvantages. The weight-in-water method is suitable for dense mixtures with low water absorption and is easy to operate, while the wax seal method is suitable for mixtures with higher water absorption and can provide more accurate gross bulk density data. By selecting appropriate test methods, the performance of asphalt materials can be evaluated more accurately and provide a reliable basis for engineering construction.
