Greg Reader, George Reed Inc., and Dave Aver, City of Santa Rosa, present on the various relationships between the material and mix characteristics and how they are used to adjust the mix design to meet the project requirements. Presentation delivered on Nov. 7, 2019 at the California Asphalt Pavement Association Fall Asphalt Pavement Conference in Sacramento, Calif.

1. Troubleshooting
the JMF
THE ROAD TO SUCCESS IS PAVED WITH ASPHALT!

2. Introduction
 Plant Processes Overview
 Learn about the various relationships between the material and mix
characteristics.
 The impact of good lab 101 testing protocols.
 The power of data
 When should you make changes
 Scenarios

3. HMA Batch Plant
 Batch plant
 Produce mix in batches (1.5 to 10 ton) in pug mill
 Materials proportioned by weight in weigh hopper
 Aggregates dried prior to mixing
 Think of this style plant as a food buffet!
 RAP is introduced directly into the pugmill, but does NOT go through
the dryer.
 Both plants require superheating the virgin aggregate with use of
RAP.

4. Batch Plant Elements
Batch Tower
Storage
Silos
Cold Feed Bins
Asphalt
Binder
Tanks
Secondary
Dust
Collector
Primary
Dust
Collector
4

5. HMA Batch Plants

6. Continuous Drum Plants
 Drum plant (continuous mix)
 Cold Feed, Binder and Additive are metered
 Aggregate dried prior to binder introduction in the drum
 Binder mixed in the drum or in an external coater
 Binder added near end of mix/drying
 RAP is introduced through a “RAP collar” in between the drying and
mixing chambers
 Both plants require superheating the virgin aggregate with use of
RAP.

7. Drum Plant Elements
Storage
Silos
RAP Bin
Slat Conveyor
Dryer/Mixer
Cold Feed Bins
Asphalt
Storage
Tanks
Secondary
Collectors
7

8. Continuous Drum Plants

9. Material Relationships
– We’re all related
somehow!

10. Basic Concept of HMA/WMA
Design
 Superpave and Hveem mix designs are
based on optimizing the volume of
aggregate, asphalt binder and air voids.
The key here is volume not weight. While
weight is used to control the amount of
material metered into the mix at the
asphalt plant, determining what that
weight should be is based on volume.
 The primary items are air voids and binder
volume which combine to become voids in
mineral aggregate (VMA).
 These are all volume proportions of the mix
and asphalt and aggregate proportions
are set to optimize these volumes.

11. Material Relationships

12. Material
Relationships
 As we have learned earlier –
binder content has an impact on
all of the volumetric properties,
but what else can impact mix
volumetrics?
 Aggregate Specific Gravity
 Aggregate Gradation
 #200s – Dust Proportion
 Particle Shape and Texture
 RAP

13. Material Relationships
 Influence of Aggregate Specific Gravity
 This has MAJOR impacts
 Changes the volumetric proportions of Aggregate to Binder to Air Voids

14. Influence of Gradation –
Will all 3 gradings produce the same results?

15. Dust Proportion and
impact of Passing the
#200’s
 Up to a certain amount, it will stiffen your
binder (Mastic)
 After a certain amount, it will act as an
extender as it gets between the aggregate
and the asphalt binder film layer.
 Your dust to binder ratio is a good indicator of
balancing binder stiffness vs flexibility of the
mix.

16. Particle Shape and Surface Texture
 Marbles vs Cubes = Affects particle interlock and stability of mixture
 Flat and Elongated = Pluggers and Interceptors, Bulks up the
aggregate structure, resists compaction
 FAA (Fine Aggregate Angularity) Affects VMA, Higher VMA is less
workable, harder to compact.

17. RAP
 Binder
 Moisture
 Binder Grade
 Gradation
 Processing for homogenization

18. Lab 101-
Good Testing
Practices =
Reliable
Data

20. Lab 101- Good Testing Practices =
Reliable Data
 Follow your established QMS for accreditation.
 Proper sampling and Sample Preparation are of the utmost
importance.
 Ensure you are following the proper test procedures – Have copies
on hand during testing!
 Always finish on the same scale you start a test on.
 Clean and maintain your testing equipment on a regular schedule.

21. Lab 101
 Have some SOPs or Best Practices in place to handle “Out of Spec”
test results.
 Retest a split of the “Out of Spec” material.
 Always look inwards first, review your sample prep and testing
process for any deviations that could impact the results before
reporting.
 Notify relevant parties as soon as confirmed that the material is “Out
of Spec”

22. Lab 101
 Good record keeping
 Old School file cabinets
 Use of database software
 LASTRADA Partners
 Stonemont
 Spectra QEST
 Microsoft Access
 Microsoft Excel

23. The Power of Data!

24. Data Management
 LASTRADA Partners Slide
 Tracking mix properties in production along with plant changes, to find
when a plant is working too hard to stay in specification.
 Example; no failing tests, but 9 plant changes in 12 sublots

25. Data Management
 LASTRADA Partners Slide
 Looking at changes in source feed gradation and make preemptive
plant adjustments
 In this example red dashed line represents mix design, blue represents
current blend estimate. Current settings expected to be too fine on #4
and #8 sieves.

26. Data Management
 LASTRADA Partners Slide
 KISS – Keep It Short and Simple, too much information clouds the view
 In this example KPI shows how many failing tests / number of tests,
%within specification and simple graphic showing average and
standard deviation relative to specification.

27. Data Management
 Stonemont Example

28. Data Management
 Stonemont Example

29. Data
Management
 Stonemont “Mix Risk” tool
 Statistical Analysis based
upon theoretical samples
and Standard Deviations of
each product.
 Helps to refine selection of
JMF Target Values for PWL or
QC/QA type projects.

30. When should we make changes?
 LASTRADA Partners
 There are of course standard statistical summaries. I like to include the
running average of tests in these summaries to remove the influence of
any one test.
 In this example never is the
average of 4 on target

31. When should we make changes?
 LASTRADA Partners
 There are of course standard statistical summaries. I like to include the
running average of tests in these summaries to remove the influence of
any one test.
 In this example the 3/8”
jumps up 3%, but the running
average is not affected until
multiple tests are in that same
range.

32. Scenario
 During your plant trial, the mix looks dry but the binder content and
gradation are on target. Frustrating-right?
 If this is a RAP design, first thought would be that the actual RAP binder is
too low. Make sure your RAP pile is homogenous throughout-very important.
 If the RAP is accurate then the culprit could be aggregate gravities. If the
aggregate gravities are not correct all the basic mix properties will be off.
 Identifying when there are problems with aggregate gravities (Gsb) can be
very difficult. If the Gsb are actually lower than those used in JMF the
effective binder and VMA would be lower than reported.
 Following slide shows inaccurate and accurate specific gravities (Gsb) of
the aggregate and the issues associated.

33. What happened?
Specific Gravity
Changed to
Volume
Relationship
Delta=0.58
Gse Design 2.657 2.657
Absorbed AC 0.40 0.98
Delta=0.90
Pbe Design 3.6 3.1 Delta=0.50
Air Voids Va 4 4
VMA Design 12 11.1
Pb Design 4 4
Ps Design 96 96
Gmb Design 2.399 2.399
Gmm Design 2.499 2.499
Mix Design Comparison Using Different Bulk Specific Gravities of the Aggregate
Mix design properties Incorrect Gsb Correct Gsb
Mix Design Combined Gsb 2.631 2.591 Delta=0.04

34. Questions and Discussion