Dave Aver, City of Santa Rosa, and Greg Reader, George Reed Inc., deliver a presentation on Superpave Mix Designs, test methods and how the results are incorporated in the final Job Mix Formula. Presentation delivered on Nov. 7, 2019 at the California Asphalt Pavement Association Fall Asphalt Pavement Conference in Sacramento, Calif.
6. Dense Graded Asphalt Mixture
• Most Commonly used mixtures
• Can be base course, Intermediate course or surface course.
• Proper thickness of layer vs NMAS size 3:1
7. Gap-Graded or Stone Matrix Asphalt (SMA)
• Caltrans Minimum Binder content of 7.5% TMM
• Improved Skid resistance
• Decreased road noise
• Wearing course
8. Open Graded Friction Course
• Wearing course
• Improved Skid Resistance
• Reduces spray from rain on the roadway
• 10%+ Air Void Structure = High Permeability
• Different Design Methodology based upon drain down of binder
10. Ultimate Objective
• Find the most economical and best performing combination of
aggregate and binder content.
• Find the aggregate structure that can carry the most amount of
binder while resisting permanent deformation.
• Durability vs Stability = BMD Cracking vs Rutting <- Future of our
Industry
• Aggregates are the skeleton – Approximately 92% to 96% of the
mixture.
• Binder is approximately 4% to 8% of the mixture
11. Objectives of the Mix Design
• Resistance to Permanent Deformation aka Stability
• Fatigue Resistance
• Low Temperature Cracking
• Moisture Resistance
• Durability
• Skid Resistance
• Workability
12. Resistance to Permanent Deformation
• Roadway Stresses
• Speak about the picture of rutted roadway
13. Fatigue Resistance
• Speak about different causes of the failure type ie subgrade
failure vs mix too brittle
16. Consensus Aggregate Properties
• Aggregate properties that are required for a good pavement,
regardless of specific source i.e. particle shape and clay content
(SE).
• Cubical vs Marbles
• Different requirements depending on traffic levels and which layer
within the structural section
19. Source Aggregate Properties
• These are specific to individual source and geology
• Can have significant impact on mixture performace
• Toughness
• LA Abrasion
• Micro-Deval
• Soundness – Sodium Sulfate or Magnesium Sulfate
• Deleterious Materials – Clay Lumps and Friable Particles
• Gradations of each aggregate size fraction
• Specific Gravity
21. Evaluate Multiple Mix Trials
• Select Trial Gradations based upon blending of source aggregates
to meet the intended specification or Historical Source Data and
information.
• Estimate Trial OBC for Single Point Volumetric Analysis and
comparison.
• Lab Batch, cure and compact, test for physical properties.
32. Moisture Resistance
• Wet/Dry = %
• Caltrans looks at Retained Strength rather than TSR Wet/Dry
• Wet = 70 PSI
• Dry = 100 PSI Min - 300 PSI Max
• Different treatment methodologies based upon specifications and
aggregate qualities.
33. Moisture Sensitivity – AASHTO T283
• Fabricate Briquettes in 2 sets of equal air void content 7.0% +/-
0.5%
• Saturate Wet Group to 70% - 80% of the volume of air voids.
• Freeze Wet group
• Trying to destroy the bond of oil to aggregate with moisture
• Minimum Wet Strength of 70 PSI
• Dry Strength has a range of 100 psi to 300 psi
• Ratio of wet to dry strength
34. AASHTO T324 Hamburg Wheel Track
• Frabricate Samples in 2 sets of equal air voids
• 7.0% +/- 0.5% Air Voids
• Test Temperature based upon PG Grade of Mix
• Maximum Rut Depth of 12.5mm
• Number of Cycles dependent upon type of mix classification,
Dense Graded vs RHMA-G
38. Caltrans CEM 3511, 3512, and 3513
• Caltrans form CEM 3511 is your JMF
• It shows the combined gradation of the mix plus the tolerance
band.
• It identifies the OBC of the JMF
• The source of all the constituent products
• Project information
• Filled out by the Contractor/Producer/Lab of Record
• Checked by Project RE for compliance with project specials and
standard specifications.
39. Caltrans CEM 3511, 3512, and 3513
• Caltrans form CEM 3512 is Mix Design Data sheets
• Includes all of the physical properties of the constituent products
used to develop the mix design.
• All of the volumetric testing of the mix design at the chosen
proportions.
• Lab verification of OBC along with performance tests at Optimum
Binder Content that was selected.
• Volumetric Charts for analysis of Lab Design
40. Caltrans CEM 3511, 3512, and 3513
• Caltrans for CEM 3513 – GOLDEN TICKET to Willie Wonka's Factory!
• This is your mix approval from Caltrans
• You obtain this by producing the JMF through the plant and
sampling with a Caltrans District lab.
• The District lab will test for the volumetric properties of the
aggregates, the HMA/WMA/RHMA, the binder used, and the
performance tests TSR and Hamburg to ensure compliance with
the specification and the JMF submitted.