Warm Mix Asphalt Phase II: Evaluation of WMA Quality Assurance Testing Protocols

Project Details









Iowa Department of Transportation
Iowa Highway Research Board

Principal Investigator
Chris Williams

Director, AMPP

Student Researcher(s)
Ashley Buss

About the research

Phase II of this study further evaluated the performance of plant-produced warm-mix asphalt (WMA) mixes by conducting additional mixture performance tests at a broader range of temperatures, adding additional pavements to the study, comparing virgin and recovered binder properties, performing pavement condition surveys, and comparing survey data with the Mechanistic Empirical Pavement Design Guide (MEPDG) forecast for pavement damage over 20 years of service life. Further objectives detailing curing behavior, quality assurance testing, and hybrid technologies were as follows:

  • Compare the predicted and observed field performance of existing WMA trials produced in the previous Phase I study to that of hot-mix asphalt (HMA) control sections to determine if Phase I conclusions are translating to the field
  • Identify any curing effect (and timing of the effect) of WMA mixtures and binders in the field
  • Determine how the field-compacted mixture properties and recovered binder properties of WMA compare to those of HMA over time for technologies common to Iowa
  • Identify the protocols for WMA sample preparation for volumetric and performance testing that best simulate field conditions

To comprehensively study WMA materials, multiple WMA technologies were included for a variety of asphalt mixtures that were monitored by a yearly pavement conditioning survey. Eleven field-produced mixes were constructed throughout the state. The equivalent single axle load design levels ranged from 300 thousand to 10 million. The WMA technologies studied included Double Barrel Green Foaming, Sasobit, and Evotherm.

Testing included performance grading of virgin binder and recovered binder from field cores. Mixture performance testing included five performance tests to incorporate all in-service temperatures for measurement of material properties and performance indicators.

Phase I performance data is presented with the Phase II results for simple data comparisons as well as for advanced statistical analysis. Phase I and Phase II mixture performance tests include dynamic modulus, flow number, and indirect tensile strength. The performance tests added for Phase II were the Hamburg wheel tracking test and the semi-circular bending test.