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Extending the Life of Asphalt Mixes David Lee, P.E. - ARAC Chair, Salem District Materials Kevin McGhee, P.E. – ARAC Secretary, VCTIR.

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Presentation on theme: "Extending the Life of Asphalt Mixes David Lee, P.E. - ARAC Chair, Salem District Materials Kevin McGhee, P.E. – ARAC Secretary, VCTIR."— Presentation transcript:

1 Extending the Life of Asphalt Mixes David Lee, P.E. - ARAC Chair, Salem District Materials Kevin McGhee, P.E. – ARAC Secretary, VCTIR

2 OUTLINE Background on Need for Research Study Results from Previous Research Project Phases Results from Latest Phase Potential Steps Forward in

3 Background There is a clear perception by both VDOT and Industry leaders that our present Superpave mixes do not have enough liquid asphalt content and, as such, are not lasting as long as they could. This perception is supported by some recent data suggesting that our mixes are lasting 1-3 years less than previously determined. (McGhee/Clark) Majority of failures occurring due to age related cracking/fatigue Research Report by G. W. Maupin “Investigation of Optimized Mixture Design for Superpave Surface Mixtures” recommended additional research on the subject. 3

4 RESEARCH QUESTION Are dense graded mixes designed with SUPERPAVE system providing consistently longer service life compared to previous mixes? Criteria for Life Durable or Fatigue resistant Rutting resistant No flushing Skid resistant (surface mixes) Research Objective – Maximize the service life of dense graded asphalt mixes

5 PREVIOUS RESEARCH PHASE RESULTS Phase I – Superpave Designed Mix Analysis Comparisons Volumetrics for 50 and 65 Gyrations Volumetric results for 50 and 75 blow Marshall Mix gradations Bag samples for future phases

6 VTM – SM 9.5 Mixes 6 Superpave Marshall

7 VMA – SM 9.5 Mixes 7 Min. (Sup. & Marshall

8 RESULTS FROM PHASE I VTM – Superpave Gyratory (SGC) produces approximately 2% lower VTM than the Marshall hammer. VMA – SGC produces approximately 1-2% lower VMA than the Marshall hammer. Review of the data did not produce a definitive “simple solution” (i.e., just reduce the number of gyrations). 8

9 LATEST PHASE RESULTS Sampled plant produced SM-9.5 mixes Targeted mixes with 23% or less passing #30 sieve and at least 58% passing #4 sieve Collected materials to do: 1.Determine AC content, gradation and volumetrics of Spec produced mixes 2.Determine VTM and VMA for mixes at 50 gyrations 3.Calculate binder needed to meet 3.5% VTM at 50 gyrations (new optimum AC) 4.Performance test initial mix, mix at optimum, mix at optimum plus 0.2% binder, and mix at optimum plus 0.4% binder 9

10 VOLUMETRICS AND GRADATIONS FOR MIXES 65 GYRATIONS 10

11 VTM vs. Added 50 Gyrations 11

12 VMA vs. Added 50 Gyrations 12

13 FLOW NUMBER vs. ADDED BINDER (VTM = 7%) 13

14 FE INDEX vs. ADDED BINDER (VTM = 7%) 14

15 The Bottom Line We know we need mixes that have a longer fatigue life to prolong the development of cracking. We know we need to ensure that any added AC does not lead to rutting or bleeding. We believe the aggregate gradations need to be tighter on certain sieves as well as the addition of one or more control sieves (#30 and #4) to combat mix tenderness and rutting. We know higher RAP is not a bad thing, but the overall mix must be considered to get the right AC and gradations. 15

16 POTENTIAL NEXT STEPS Finalize select use special provision for SM-9.5 with changes to: Design Gradations (#30 and #4 sieves) Design Gyrations (50) Solicit demonstration projects from across state Design and produce experimental mixes Pave control (65 gyrations and 4% VTM) and experimental mixes Retrieve mix (control and experimental) for additional lab performance testing Flow Number and APA for rutting Fracture Energy for cracking Collect density data from control and experimental sites 16


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