Using quality materials is critical to having durable construction projects. Hence, you should test the materials used in any construction. The specific gravity of the asphalt test is one of the tests used to determine the quality of asphalt used for construction projects. It ensures asphalt meets desired performance criteria to deliver quality construction works.
How do you conduct the specific gravity of asphalt test? This article will explore how to carry out this test.
Let’s start the discussion by explaining what it is and why it is important!
What is the Asphalt Specific Gravity?
Asphalt specific gravity is the ratio of the density of asphalt to the density of an equal volume of water at the same temperature.
It is also known as the theoretical maximum specific gravity (Gmm) of asphalt, as it measures the specific gravity excluding air voids. That is, it looks at the specific gravity of an asphalt sample if all the air voids were eliminated from the sample.
The asphalt-specific gravity is an important property to consider in construction because it helps you assess the density and compactness of the material.
Knowing the asphalt-specific quality enables you to calculate air voids in the compacted mix and establish good targets for compaction during laydown to deliver durable construction works.
Thus, asphalt-specific gravity is a fundamental property of the material that affects the quality, performance, and durability of asphalt pavements.
Keep Reading: Understanding the Slump Tester & Its Uses.
Why is the Specific Gravity of Asphalt Important?
It is important because it provides valuable information about the quality of the HMA and affects the performance and durability of asphalt pavements.
Key reasons why it is important include:
Quality Control and Mix Design
You can use the specific gravity of asphalt as a quality control measure when producing asphalt measure. Deviations from the desired specific gravity can indicate issues with your mix proportions.
You can then correct the amount of aggregate and binder in the asphalt mix to achieve the desired performance characteristics for a specific application.
Density and Compaction
Specific gravity can help you ensure that asphalt is compacted to the desired density. This is related to its density. A higher specific gravity indicates a denser, more compacted asphalt mix.
Proper compaction of asphalt results in higher stability and pavement strength.
Void Content
You can use the specific gravity of asphalt to estimate the void content in an asphalt mix. The volume of voids is determined by the density of aggregates and bitumen in the asphalt mixture.
If the percentage of air voids is too high, the pavement exhibits decreased strength. But if the percentage of air voids is too low, pavement damage like rutting and shoving can occur.
After using specific gravity to calculate the volume of voids, you can then make the necessary adjustments to obtain quality asphalt mix with proper percent air voids that deliver pavements with high load-bearing capacity and durability.
Performance Prediction
This affects the performance of asphalt pavements. So, you can use the measurement to predict the performance of asphalt pavements.
You can use the specific gravity of asphalt in various models to calculate fatigue resistance, rutting resistance, and thermal cracking resistance of asphalt pavements.
More read: Shear Vane Tester: Understanding Soil Stability.
Equipment for Testing the Specific Gravity of Asphalt
The ASTM and AASHTO standards for testing the specific gravity of asphalt allow for slightly different methods. Therefore, the equipment for the test will vary slightly, depending on the particular method chosen.
That said, some of the most important equipment for the test are:
Rice Shaker
The rice shaker or deaerator provides consistent mechanical agitation of the vacuum container during the vacuuming operation to completely remove all entrapped air in the container.
Vacuum Pump
The vacuum pump is used to remove free air from the vacuum container to a residual pressure of 4.0kPa (30 mmHg) or less.
Drierite Laboratory Air/Gas Dryer
The Drierite Lab Air/Gas Dryer prevents moisture from entering and damaging the vacuum pump when vacuuming to remove free air from the pycnometer/ flask.
Pycnometer
The pycnometer is the vacuum container that holds the asphalt sample when measuring the specific gravity of asphalt.
Flask
When you choose suspended weighing, you’ll use a specific gravity bottle or thick-walled filter flask as the vacuum container to hold the asphalt sample for the specific gravity test.
Absolute Pressure Manometer
The Absolute Pressure Manometer is a mercury-free and environmentally friendly pressure gauge to confirm that the specified pressure is applied when vacuuming to remove free air from the container.
