Advancing Asphalt Mixture Design through Application of Planar Imaging Techniques and Asphalt Lubricity Testing to Improve Understanding of Effects of WMA on Mixture Workability

Quarterly Reports Other Documents Final Report
December 2012
March 2013
March 2014
Final Report

Primary Investigator

Hussain Bahia, Ph.D
Department of Civil and Environmental Engineering
University of Wisconsin-Madison


Warm mix asphalt (WMA) presents an opportunity to reduce the environmental impacts of asphalt paving by allowing for production at temperatures up to 50°C lower than conventional HMA. The potential impact is significant as World Bank estimates indicate that every 10°C decrease in production temperature corresponds to savings of nearly 1 L of fuel oil and 1 kg of CO2 emissions per ton of asphalt mix produced. Warm mix technologies include plant or process modifications to promote foaming during production or use of additives pre-blended with the asphalt binder. In practice, these technologies are applied to conventional mix designs and allow for production at lower temperatures by modifying the properties of the asphalt binder or interactions at the asphalt/aggregate interface. To be deemed successful WMA is required to achieve in-place density at lower construction temperatures and demonstrate similar in-service performance to conventional HMA. In regards to construction, previous research has established that conventional viscosity-based methods used to determine mixing and compaction temperatures do not apply to WMA as the test method severely over-predicts the production temperatures used in the field. Furthermore, the effect of compaction temperature on density was found to be mixture specific, preventing definition of a threshold value of viscosity to control density. As a result, a method for selection of production temperatures based on laboratory mixture compaction at different temperatures developed in NCHRP Report 691 has been adopted for selection of mixing and compaction temperatures for WMA.


There is a need to build on the concepts presented in NCHRP Report 691 in development of a new methodology to select mixing and compaction temperatures for HMA and WMA that moves beyond the traditional approach of controlling asphalt binder viscosity to achieve a certain level of density. Asphalt mixture density is governed by formation of aggregate structure during compaction. In this process the asphalt binder acts as a lubricant, facilitating re-orientation of aggregate particles under compactive load. Based on this concept there is a need to advance the science currently used in the asphalt industry to characterize the lubricating properties of the asphalt binder and establish a relationship with development of aggregate structure. The aggregate skeleton created after compaction contributes significantly to the in-service performance of mixtures, this research will also define the effects of changing compaction conditions on final aggregate structure and measure the impacts on mechanical performance. The end result of this research will be a guideline to select of mixing and compaction temperatures based on achieving the appropriate aggregate structure required for mechanical performance.


  1. Development of asphalt lubricity test.
  2. Determine factors impacting development of aggregate structure and effects on performance.

Project Information

  • Duration: 18 months
  • Dates: August 1, 2012 – November 30, 2013
  • Budget: $115,000 ($70,000 in matching funds)
  • Modal Orientation: Highway
  • Project ID: CFIRE 07-09
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