Nuclear Density Gauge Testing: Soil & Asphalt Compaction

For most people, even to this date, the word "nuclear" is a trigger and a source of fear. As many experts have pointed out, fear is a product of the unknown. When something is not understood properly, it causes fear. When we discuss nuclear density testing, it's important to understand the basis of the testing method and be able to explain it in non-technical terms. For some of us, it's just another tool whose benefits depend entirely on how we operate it.

Nuclear density gauges offer a great advantage for determining soil and asphalt compaction. The operation of these nuclear density gauges requires specialized training and certification. Nuclear density gauge testing is regulated by multiple entities and varies between locations. Make sure to always check local and state requirements when operating nuclear density gauges.

The gauges are portable, easy to use, accurate, and provide results in minutes. The ability of these gauges to provide fast, accurate measurements makes them very popular on jobsites, as it allows the contractor to address issues right away.

Safety & Security with Nuclear Density Gauges

Safety

Nuclear density gauges do have a radioactive source inside (or multiple). These sources emit radiation in very small and manageable quantities. However, safety is dependent on properly trained personnel and maintaining the proper shielding of the source.

Every nuclear gauge operator should be properly trained on the operation of the nuclear gauge and nuclear safety. In general, nuclear gauge manufacturers offer training, in person and online, for nuclear safety and gauge operation. Although we provide some safety tips here, this is not a course or a nuclear safety document.

Key safety practices:

• Distance and Shielding: When dealing with radiation sources, the further you are and the more solid objects are between you and the nuclear source, the less dose of radiation you will absorb. Nuclear density gauges are internally shielded to provide protection to the operator.
• Keep untrained personnel as far as possible from the gauge.
• Make yourself visible and engage in eye contact with heavy equipment operators to make sure they know where you and the gauge are.
• Inform your Radiation Safety Officer (RSO) of any issues as they arise. Do not delay.

Security

It’s of the utmost importance to maintain control of the gauge at all times. When transporting, make sure to have all the transport documents with you. In recent months, there has been a surge in stolen nuclear density gauges.

Implement additional security measures as needed to ensure control of the gauge. Our friends at the U.S. Nuclear Regulatory Commission maintain a daily log of events regarding radioactive materials. View the event notifications >

Soil & Aggregate Compaction Testing

Nuclear density gauge testing for soil or aggregate compaction is one of the most common calls for a testing lab. Sometimes the difference between "soil compaction," "soil bearing," and "soil borings" needs to be communicated, but we'll leave that topic for another blog.

As soils are compacted in layers, the thickness of those layers is governed by the geotechnical report for the project. With the nuclear gauge, we want to test the compaction of each of those layers at random locations and intervals. In order to understand if the material is properly compacted, we need to know what the maximum density achievable by that soil is. This is also known as the Proctor test.

The Proctor test will give us two values: density and moisture. We'll enter the maximum density from the Proctor test into the gauge and run the test. The gauge will compare the density of the soil in place after compaction to the max from the Proctor. How close those two values are determines the pass or fail of the compaction.

Testing soils and aggregates is, for the most part, done by "direct transmission." This means that a small pilot hole is made in the material using the template in the gauge box, and the source or rod is inserted into the compacted layer. Before starting the test, confirm the rod depth and that the rod is secured. Do not move the gauge when the test is in progress.

Always inspect the stockpiles and the material being compacted. Verify that no foreign materials or substances are mixed into the material that could cause interference with the measurements. Similarly, make sure the material is not frozen.

Asphalt Compaction Testing

Nuclear density gauge testing for asphalt compaction is similar to the compaction of soils but way hotter! For asphalt compaction, you need to communicate with the producer's plant and get the Gmm values. After being multiplied by the unit weight of water, the value is entered into the gauge. Similar to soils, the gauge will compare the maximum value with the obtained value to determine pass or fail.

The main difference for asphalt is that the rod or source is not inserted into the compacted material. The rod is outside of the shielded position and flush with the base of the gauge. Tests performed in this manner are known as "backscatter." If you don't like potholes, needless to say, don't pound the rod into the asphalt.

It’s critical to properly clean the base of the gauge after using it. More importantly, while waiting to test, don't leave the gauge resting on the hot asphalt. Prolonged heat exposure can shorten the useful life of the gauge or cause problems with the internal electronics. Find a nice, fresh, and ventilated patch of grass to set it down while the rollers go back and forth.

Best Practices for Nuclear Density Gauge Testing

Regardless of the material being tested, you should always do and record your standard count to ensure the gauge is operating properly. Standard counts can be done in Omnant and can be added to your field reports automatically.

At the end of the shift, when bringing the gauge back to the lab, it's good practice to check the battery levels and put it to charge if needed. Make sure to scan your gauge out using Omnant, or sign the sheet if you are old school. Like any other testing, practice makes perfect.

When it’s time to simplify your field inspection workflows and equipment tracking, you can depend on Omnant to deliver. See how we help construction testing laboratories manage nuclear density gauges, track certifications, and automate field reports. Schedule a demo today.