Podcast: Illinois DOT & Balanced Mix Materials Design

The latest episode of the AASHTO re:source podcast digs into how the Illinois Department of Transportation implements  their balanced mix design specification for its asphalt pavements.

[Above image by AASHTO re:source]

According to AASHTO PP 105, the “Standard Practice for Balanced Mix Design of Asphalt Mixtures,” balanced mix design uses “performance tests on appropriately conditioned specimens that address multiple modes of distress taking into consideration mix aging, traffic, climate, and location within the pavement structure.”

During this podcast episode Brian Pfeifer, engineer of materials, and Brian Hill, HMA operations engineer, explained how the Illinois DOT tries to find the right balance of asphalt paving materials that will reduce rutting and cracking of pavements while still meeting their existing volumetric design requirements.

“We are also trying to balance our use of recycled materials as well and make sure that those recycled materials are used in a way that doesn’t have a negative impact on [roadway] performance,” explained Pfeifer.

“I think that’s an important part when it comes to sustainability,” he added. “You have to keep in mind that you may be adding a material or using a material that appears to make the mixture more sustainable, but if you don’t get the longevity, if you don’t get the durability out of it, then you’re not realizing that improvement on sustainability so. It’s really about balancing between those two ends of performance.”

Hill noted that it does take a lot of time and a lot of effort to collect the data needed to determine the suitability of materials used in roadway paving operations – recycled as well as non-recycled.

“But there’s no time like the present to start collecting data for that,” he emphasized. “Because it takes a large amount of data to really, truly understand how mixtures are performing in your state with the particular specifications and standards your [state] DOT employs.”

The balanced mix design standard specification, AASHTO MP46, and standard practice, AASHTO PP 105, can be found at the online AASHTO store. Relevant links to other information about balanced mix design can be found on the AASHTO re:source podcast page.

To listen to the full podcast episode, click here.

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