1. Moisture Induced Stress Testing (MIST) to Evaluate Stripping Potential of HMA Pavements AASHTO RAC/TRB 2013 Summer Meeting Work completed by Rajib Mallick at WPI Prepared by Dale Peabody dale.peabody@maine.gov

2. Why was the research performed?  MaineDOT uses Hot Mix Asphalt pavement only – AND IT’S FALLING APART!!!

3. Why was the research performed?  HMA pavements pass the Superpave criteria  Concerns with aggregate quality, excessive dust & liquid asphalt quality  Existing method for moisture susceptibility AASHTO T283, doesn’t catch our poor performers

4. What We Did  Sampled Cores from one and two year old HMA projects  Condition core samples in MIST  Visual observations and testing on non-conditioned cores and conditioned cores

5. What we found… MIST equipment provides a better tool for helping to ID poor performers.

6. RESULTS

7. RESULTS Project Name Visual Sample Degradation* TSR BSG (Absolute percent change) Resilient Modulus (Net percent change) Abbot Monson Severe0.891.71-43.1 Dover Foxcroft Minor0.90.95-11.9 Ellsworth Minor1.090.59.7 Harrison Very Minor0.970.5714.3 South Portland Moderate0.920.54-25.0 Turner Very Minor1.060.94-36.7

8. Hamburg Wheel Tester

9. CONCLUSIONS AND RECOMMENDATIONS  1.MIST conditioned samples can ID poor performers  2.The effects of MIST conditioning should be studied further to develop standards  3. Coupled with the newly acquired Hamburg Wheel Tracker Device, can identify poor performing mix designs

10. Benefits  MIST equipment can be used immediately to help ID potential poor performers  MaineDOT to consider adopting MIST and save taxpayers $$$’s  Specification changes can be driven by test data

11. The People Part of the Program  We assigned two relatively new Department employees to lead the research. They didn’t have preconceived ideas, yet!!  We had confidential meetings with paving contractors to ask why thought pavements were failing. They provided some thought provoking answers.

12. The People Part of the Program  We shared our research with industry as we progressed. We asked for their input along the way.  We promised not to make major paving specification changes unless we could show results.  However, we expected industry to support changes to specifications if we documented issues.