Why & How to Perform the Marshall Stability Test on Asphalt

Not all asphalt is created equal — otherwise it wouldn't be able to handle the necessary loads! Using the Marshall Stability Test, engineers can predict how well an asphalt mixture will perform and the maximum load it can support. Learn more about what the Marshall Stability Test is, why it's used and how it's performed.

What is the Marshall Stability Test?

The "Marshall" in Marshall Stability Test refers to Marshall mix, which is the type of asphalt we see in roads today. The Marshall mix design method helps engineers select the optimum asphalt binder content at a density that meets stability and flow value requirements. While other tests have been developed and refined in conjunction with this test, the stability test is still one of the most widely used asphalt mix design methods worldwide.

How to Perform the Marshall Mix Stability Test

While there are quite a few steps that go into the Marshall test for asphalt, they're straightforward and simple to perform with the right equipment at your disposal.

Step 1: Aggregate Selection

Asphalt is made of two main components, bitumen and aggregates. Bitumen is the liquid binder that holds the aggregate mix together and creates the final blend we know as asphalt. To select an aggregate, you'll need to test various physical properties like toughness and abrasion, particle shape, gradation and size, durability, specific gravity and absorption. If aggregates are coming from more than one source, perform trial blending calculations until the proper mix design is achieved.

Step 2: Asphalt Binder Selection

For this portion of the test, most engineers will refer to the Superpave PG binder system since the Marshall test has no binder evaluation and selection procedure. Tests performed on the asphalt binder should determine the relationship between temperature and viscosity.

Step 3: Sample Preparation

The Marshall Stability Test typically requires a variety of sample bitumen-aggregate blends with different levels of binder content in order to determine the best one for an application. Generally, there will be 5 bitumen-aggregate blends with 3 different levels of binder — 15 specimens in total. This step allows engineers to determine the optimum asphalt binder content and which blend does the best job of handling the necessary load.

As part of sample testing, the specimens are heated to the predicted compaction temperature. Next, a Marshall compaction tool, usually a hammer, is used to compact the samples with steady pressure.

Step 4: Stability Testing

Now the true stability testing can begin. Using Marshall stability test systems like the Hveem Stabilometer, engineers can measure the maximum load a particular blend will be able to handle. Specimens are loaded at a rate of 50.8mm/minute (or around 2 inches per minute), slowly increasing until the maximum load is reached. A dial gauge will generally also measure the specimen's plastic flow due to loading.

Step 5: Density and Air Void Analysis

Finally, specific gravity tests and air void tests can be performed on the specimens to ensure they meet local and state criteria. This will ensure that the proper bitumen, aggregate and air volumes are reached for an optimal final product.

Find Marshall Test Machines & More at Certified MTP

Certified Material Testing Products carries all the Marshall test machines needed to perform Marshall Stability Tests and many other forms of asphalt testing. Have questions about a product? Contact us to speak with our team of material testing experts.