Ever driven on a bumpy road and wondered what went wrong? The fact is, it’s common to pass roads like this. And the major reason often lies in the imbalance of asphalt density. Knowing how to test density of asphalt helps to avoid this and is obviously very important, especially when you’re working on a large-scale project.
In this article, Qualitest breaks down why asphalt density matters and how it directly affects pavement quality and longevity. Keep reading for a step-by-step guide on how to test asphalt density the right way.
Let’s dive in.
What Is Asphalt Density and Why It Matters
Asphalt density is one of many features measured to determine the quality and quantity of asphalt, particularly in the context to pave a road. In simple terms, it refers to how much material is packed into a specific volume.
Once we understand how to test density of asphalt it would help to calculate how much asphalt is needed to meet the performance expectations. The better we understand the compacted density, the more precise we can be in estimating materials and ensuring consistent paving quality.
A uniform, well-compacted mix helps build roads that are smoother, stronger, and more durable. So, to make sure the density aligns with the expectations and requirements, professionals often refer to testing the asphalt density in compliance with the standard ASTM D70 (an international standard to measure the density of asphalt materials using a pycnometer method).
Related Content to Read: Asphalt Testing - How It Improves Road Quality, Durability, and Maintenance Planning
Methods for Testing Asphalt Density
As mentioned previously, there are several methods used in how to test density of asphalt. Two major methods commonly applied are the pycnometer and the asphalt density gauge.
Take a closer look at the explanation below:
1. Using Pycnometer
The pycnometer method is a more traditional, lab-based approach, often used when following standards like ASTM D70. In this method, the asphalt sample (usually heated bitumen) is carefully placed into a glass pycnometer (a small vessel with a narrow neck that can be quite tricky to handle).
The sample then needs to cool down to a controlled temperature, usually 20°C, before being filled with water and weighed. This method is recommended for use in a controlled lab environment.
Testing asphalt’s density using this method requires a lot of patience, steady hands, and technical skill. Since the sample must be in bitumen form, the process can be quite time-consuming. It involves reheating the bitumen, pouring it out, and then soaking and scrubbing the pycnometer clean using solvents like toluene.
2. Using Asphalt Density Gauge
For faster and more practical results, especially on-site, many professionals turn to non-nuclear asphalt density gauges. This device offers a modern alternative to traditional methods by using advanced sensor technology to instantly measure density, moisture content, and compaction levels, without dealing with hazardous materials.
Non-nuclear asphalt density gauges, like QualiADG are equipped with a full-color touchscreen and an intuitive interface that’s easy to operate. Data can be accessed, stored, and exported via USB in just a few seconds. This method should be implemented in compliance with ASTM D7113 and AASHTO T343 standards.
Equipment Used in Asphalt Density Testing
Answering how to test density of asphalt, relies on the use of proper instruments tailored to the chosen test method. Each method requires specific equipment to ensure valid and repeatable results.
Below is an overview of the commonly used tools in both the pycnometer method and the non-nuclear asphalt density gauge method:
For Pycnometer Method (Laboratory-Based)
- Glass Pycnometer: A precision vessel used to contain and measure the asphalt sample. Must withstand temperature control and fluid measurements.
- Analytical Balance: High-accuracy weighing scale (0.01g or better) to measure mass before and after filling.
- Temperature-Controlled Water Bath: Maintains a consistent testing temperature (typically 20°C) during measurement.
- Oven or Hot Plate: Used to heat and soften bitumen before placement in the pycnometer.
- Toluene or Mesitylene Solvent: Required for post-test cleaning of the pycnometer to remove residual bitumen.
For Non-Nuclear Asphalt Density Gauge (Field or Lab-Based)
- Non-Nuclear Asphalt Density Gauge Unit: Equipped with integrated sensors and GPS for on-site use.
- Internal Data Storage & USB Export System: Allows real-time data logging, transfer, and project file management.
- Battery-Powered Operation: Suitable for portable, on-site test use without involving external power.
Step-by-Step Guide: How to Test Asphalt Density in the Field
Field testing asphalt density using a non-nuclear gauge, like the QualiADG is an efficient, secure, and user-friendly method. Here’s how to properly conduct the test in line with industry standards and device capabilities:
1. Set Up the Control Strip
Begin by paving a designated control strip. This area is used to establish the proper roller pattern and number of passes.
- Use the QualiADG to take five random readings across the strip using either Single Mode (for fast readings under 5 seconds) or Average Mode (which stores five consecutive readings with timestamps).
- The target optimum density is defined as when the average density no longer changes by more than 1.0% between passes, and falls within the 90–97% density range.
2. Verify Readings with Core Samples
After recording initial readings, extract core samples from the same five points. These samples are used to verify the accuracy of the gauge and calibrate it if needed.
The QualiADG supports normal calibration mode which allows correlation offsets to match core density values.
3. Conduct Daily Density Readings
Once paving begins, take routine readings. As each reading considering the following action:
- Take at least 10 random QC/QA readings per day, or 2 readings per 500 tons of mix (consider which one gives a higher frequency).
- All readings are automatically logged in the device’s internal storage and can be tagged by project and mix name using the gauge's built-in Mix Details and Project Details feature.
- If the lot average falls 2.0% or more below target, and density drops under 92%, a new control strip must be constructed and verified.
4. Perform QA Sampling for Large Projects
Check the daily takes of the samples. For production volumes exceeding 500 tons per day:
- Extract 2 QA core samples daily.
- Compare the average of the 2 gauge readings with the average core density. If the difference is within 3.0 lb/ft³, the daily gauge results are accepted. Otherwise, recalibration and a new control strip are required.
Related Content to Read: Types of Asphalt Testing: Methods, Standards, and Equipment Used in Asphalt Quality Control
Tips for Accurate Density Testing
Accurate asphalt density testing involves a well-executed process in the field. No matter what methods you’re going to use, remember, small mistakes can lead to big inconsistencies.
Therefore, let’s highlights some hands-on tips below to help keep your results reliable and your work on track:
1. Establish a Proper Control Strip
A good control strip acts as your reference point. It helps determine the right rolling pattern and number of passes needed to reach optimal compaction. Take your time during this stage to set the baseline for everything that follows.
2. Stay Consistent with Test Procedures
Follow the same process every time, such as take the same number of readings, same depth, and same position relative to the lane. Inconsistent asphalt testing practices can make even accurate equipment seem unreliable.
3. Keep Equipment Clean and Calibrated
Make sure sensors, plates, and any test surfaces are clean before each reading. Dirt, debris, or temperature swings can throw off results. If needed, recalibrate the tool according to standards or core sample comparisons.
4. Watch Your Test Depth
Make sure you're measuring at the correct depth specified by your project or standard. Especially with portable devices, incorrect placement can affect how much of the compacted layer is being measured.
5. Log Data Carefully
Label your readings with relevant mix details, locations, and time. Either you're writing it down or using software, organized records help track patterns and troubleshoot inconsistencies if they show up later.
6. Be Mindful of Temperature
Asphalt temperature can affect compaction and readings. Try to test under consistent temperature conditions when possible, or at least take note of any fluctuations during testing.
Final Thoughts
In sum, how to test density of asphalt, after all, involves close attention, consistency, and solid preparation. It also means being flexible and responsive to external factors, like the weather. On colder days, for example, the mix cools faster, which means you’ve got less time to reach the right density before it stiffens.
That’s why your tools need to be ready for the job. Using a portable tester can make things easier, especially when you're working across different environments and need both flexibility and accuracy.
And if you're already using a non-nuclear asphalt density gauge, don’t forget: regular calibration and maintenance are essential. Just like the mix you’re testing, your equipment needs care to deliver consistent, trustworthy results.
Still unsure which equipment fits your project best? Let’s talk. We’d be happy to recommend a compact solution for fieldwork, a safer alternative to nuclear gauges, or simply offer advice on what works best for your needs.
