By Dr. Amma Agbedor, Ph.D., P.Eng.
Advancing asphalt: A novel approach to assessing mixture workability
What is workability?
Workability, in the context of material properties, refers to the ease with which a material can be shaped, formed, or manipulated into a desired form without fracturing or damaging the material. It’s an important property in various fields such as engineering, construction, and manufacturing, where materials need to be processed or worked on to create final products.
In the context of asphalt mixture, workability refers to the ability of an asphalt mixture to be placed and compacted effectively during the construction of asphalt pavements. Workability is one of the main factors that influence the compaction quality and ultimately the performance of asphalt pavement, therefore it plays a significant role in the overall performance and durability of the pavement.
You can imagine my excitement when I learned there was a new test method (ASTM D8541-23) published in January 2024 to evaluate the workability of asphalt mixture using a wireless particle-size sensor… Asphalt Institute’s Mike Anderson can tell you – because he shared it with me. I had to share it as the first topic for our Smart Asphalt series.
A new workability test method
The test method uses a loose mix that has been subjected to appropriate conditioning for Superpave asphalt mix design that is ready for compaction. At the end of the conditioning period, half the mixture is placed in the mold, then the wireless particle-size sensor is placed on a flattened surface of the mix before the remaining portion of the mix is loaded into the mold. The wireless sensor collects compaction data during the compaction process, including quaternion data which is used to represent rotations in three-dimensional space. The data can be used to calculate the average relative rotation in the x- and y-directions, and the relative rotation capacity is determined by calculating the area under the relative rotation curve from the Nini to Ndesign gyration levels in the SGC (Superpave Gyratory Compactor).
How to use the test
The test can be used to determine the relative rotation of laboratory-produced and plant-produced asphalt mixtures, regardless of the type or gradation of the aggregates, and whether reclaimed asphalt pavement (RAP), warm mix asphalt (WMA) additives or any type of modifiers are used in the asphalt mixtures. This is very much applicable in research to determine the compaction temperature and optimal dosage rate of additives or modifiers to achieve the best workability for modified asphalt mixtures. Researchers believe the more active the particle rotation the better the workability.
If you’re wondering whether this can be used in quality assurance or acceptance, the test method is not intended for that purpose, however, you can certainly use it for field trials to compare modified mixtures and conventional mixtures as part of the data collection. Typical asphalt mixture specifications don’t currently include specific requirements for workability. However, it is indirectly measured and considered through other tests and parameters that are part of the mix design including aggregate gradation selection, asphalt binder content, compaction curves from the SGC which is a one-dimensional measure, Marshall stability and flow test and rutting tests.
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