2/5/2019 Mixture Design Part 2: Maintaining the Balance Shane - - PDF document

2/5/2019 1

Mixture Design Part 2: Maintaining the Balance Shane Buchanan CRH Americas Materials Learning Objectives

1.

Review the fundamentals of asphalt mixtures and know what drives performance and economics.

2.

Understand the importance of mixture materials consistency.

3.

Emphasize how to manage and characterize recycled products to ensure optimum addition levels and benefit.

4.

Understand what can go wrong during production relative to the mix design and what steps to take to help ensure quality production.

5.

Learn how asphalt performance testing can be used for mixture

• ptimization within or outside a balance mixture design

approach.

Session Highlights

 This session will present fundamental principles that will assist

in the design and production of a higher quality, more consistent, and more cost effective mixture.

 Discussion items will include volumetric property fundamentals,

materials (binder, aggregate, and recycle) characterization and consistency, stockpile moisture considerations, and mixture performance testing and analysis.

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Mix Design Fundamentals

 A good mix design can help limit the

number and magnitude of production issues and make it easier to control or maintain the balance achieved during design.

 Critical information/relationships must be

known during the design process.

The Mix Design



Aggregate / Recycle / Binder

 Aggregate gravities and absorption  Recycled aggregate gravities  Current particle size gradings  Relationship between gravities  Asphalt binder continuous grading  Recycled binder continuous grading 

Volumetrics

 Air voids, voids in mineral aggregate, voids filled with asphalt,

etc.

 Relationship of each property to one another and to

binder content (e.g., how sensitive is the mix to binder changes)

 Should be done for each unique mix!  Phase diagram fundamentals

Information You Must Know!



Other items

 Additives (Dosage, Calibration,

Impact)

 Liquid anti-strip  Hydrated lime  Rejuventors  Warm Mix  Asphalt rubber

2/5/2019 3

Aggregates

 Main component of asphalt mixes

 ~ 95% by mass and ~85% by volume in a typical mix  A primary driver of mix consistency and performance

Aggregates

Gs

Aggregate Gravities

Archimedes

2/5/2019 4

Specific Gravity and Absorption: Basic Building Blocks

• Specific gravity (Gs) is the ratio of aggregate

weight to the weight of an equal volume of water – Dimensionless number (no units attached)

• Materials can be in varying moisture conditions. Oven dry and saturated surface dry (SSD) are key conditions.
• Saturated surface dry is achieved when the surface of an aggregate particle or mix are "dry“ (no free moisture),

but the surface voids are fully saturated with water.

• Internal voids are not typically considered for aggregates, but make up the air voids in a compacted asphalt mixture.

Aggregate and Asphalt Mixture Moisture Conditions

Oven Dry Saturated Surface Dry Partially Saturated Free Moisture Surface Voids Internal Voids Note: Schematics illustrate an aggregate particle, but the principles hold true for a compacted asphalt mixture (lab or core).

• Asphalt phase diagram components follow the standard naming convention

shown below.

Volumetric Naming Convention

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Aggregate Apparent Specific Gravity, Gsa Aggregate Specific Gravity Relationships Water Absorption

SSD weight - Oven dry weight Oven dry weight

Aggregate Particle Permeable Surface Voids Filled with Water

Abs, % = X 100

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 Gse is an aggregate property

 For a given mix design, the relationship between Gse to

Gsa and Gsb should not change (within test variability)

 Relationship may change based on mix temperature

(binder absorption)

 If mix temperature is constant and a change is seen,

something has changed in the aggregate blend (e.g., “heavy vs. light” aggregate).

 Aggregate Control Chart

 Develop control chart showing the Gsa and Gsb of the

aggregate blend and the Gse determined values.

 Identify trends before problems show up.

Aggregate Effective Specific Gravity

Factor Effect on Gs Aggregate Mineralogy Aggregate mineralogy has inherent variability Fine Aggregate Dust Content Higher dust contents can lead to falsely low Gsb and high absorption Aggregate Shape / Texture

• Possible. Could impact saturated surface dry determination

Aggregate Grading

• Possible. Perhaps more with fine aggregate

Sampling Error Absolutely

Factors Influencing Aggregate Specific Gravity

Questions to ask…

• 1. Is the specific gravity of a given pit/quarry expected to remain constant?
• 2. How variable is the specific gravity of your aggregate?
• 3. How often do you check (test) the specific gravity?

If you don’t know the aggregate gravities, you don’t know your mix!

Impact of Aggregate Specific Gravity

 Understand the impact of changing specific gravity

 Variable gravities will impact volumetrics  Changing aggregate gravities can impact binder volume in

the mix

 Heavy aggregate relative to design = higher binder

volume (and vice versa), highlight importance to design for desired asphalt volume.

 0.1 Gsb ∆ = 0.2% AC ∆  Do your gravities change around your quarry/pit? Probably!  How much?  0.01 Gsb ∆ = 0.3% VMA ∆

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Recycled Products

2016 World of Asphalt Mix Optimization Fundamentals

Manage and Utilize Recycle Products for Maximum Return

2016 World of Asphalt Mix Optimization Fundamentals

• Conduct inventory analysis of recycled products
• How much do you have and how much will you use?
• How much will you be obtaining?
• Can you use this as it’s obtained? (i.e., can you add to stockpiles?)
• Evaluate the quality and consistency of the recycled products
• What is the RAP source? DOT work, general RAP, plant waste, etc.
• What is the RAS source? Manufactured waste, post consumer tear offs
• Characterize
• Evaluate impact of recycle use on asphalt binder selection and tankage

capacity

• Treat recycled products during production the same as virgin aggregates.
• At higher recycled percentages (~35 to 40%+), this is a MUST!
• Cover/paved stockpiles
• Multiple recycle bins

 Understand that millings and general RAP are different  Both can provide a good quality product, but understand they are different

What Type of RAP Do You Have?

2016 World of Asphalt Mix Optimization Fundamentals

2/5/2019 8

Take Time to Analysis RAP (Especially Grading)

2016 World of Asphalt Mix Optimization Fundamentals

 Many times, graphs can provide a more complete understanding  Suggestion: plot standard deviation along with coefficient of variation (COV) to get

complete picture of variation (BTW, do the same for virgin aggregates)

RAP Testing Thoughts

2016 World of Asphalt Mix Optimization Fundamentals

RAP Testing Thoughts

2016 World of Asphalt Mix Optimization Fundamentals

2/5/2019 9

So What are Acceptable RAP Property Tolerances?

2016 World of Asphalt Mix Optimization Fundamentals  NCAT recommendations on RAP AC and grading.  Can you make RAP with higher variability work?

 Yes, but it becomes more difficult!

RAP and Virgin Aggregate: Consistency

2016 World of Asphalt Mix Optimization Fundamentals

 NCAT study evaluated 74 RAP

stockpiles in 14 states, and 60 virgin aggregate stockpiles in 6 states

 RAP would found to have lower

grading variability

 Is this surprising? Probably

not, RAP has been sized and processed more than virgin aggregate

 Is it always the case? No, but

likely

 What is your case?

Fractionated RAP is Not Always More Consistent

2016 World of Asphalt Mix Optimization Fundamentals

 NCAT RAP Study Data (fractionated vs

unfractionated RAP)

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Utilize RAP Fractionation When Beneficial

2016 World of Asphalt Mix Optimization Fundamentals

RAP Bulk Specific Gravity (Gsb)

• Substantial VMA errors can occur if

the incorrect RAP Gsb is utilized

• Especially critical with high RAP

mixes

• VMA errors typically result in lower

than calculated effective binder contents.

Utah Asphalt Conference | February 2015 Gsb = 2.700 Gsb = 2.660

VMA = 100 - (Gmb * Ps) Gsb

Binder

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Asphalt Binder Grading

PG 64-22

Performance Grade Average 7-day max pavement design temp 64o C Min pavement design temp

• 22o C

Up or down in 6C increments

PG Binder Classification Useful Temperature Interval (UTI)

• Maximum to Minimum temperature range where the binder is expected

to perform properly.

• PG 64-22 has a UTI of 86°
• (64° - (-22°)) = 86°
• PG 76-22 has a UTI of 98°
• (76° - (-22°)) = 98°

Rule of 92

• If UTI < 92°, asphalt binder is probably not modified
• Some crude sources are exceptions – California crudes
• If UTI = 92°, most asphalt binders are modified
• Some crude sources are exceptions – Venezuelan crudes
• If UTI > 92°, asphalt binder will be modified
• Modification will increase the UTI of asphalt binder

64

• 22

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Useful Temperature Interval (UTI)

Baumgardner TRB – Trends in Asphalt Binders 2018

PG Binder Continuous Grading

• A continuous PG classification can be obtained

from the binder supplier upon request.

• Binder suppliers should have this information
• n hand for immediate submittal.
• For recycled products (RAP and RAS), the

binder should be extracted and recovered for PG binder continuous classification.

 Any given asphalt binder graded to the

most conservative 6 degree increment for the high and low temperature.

 The continuous PG classification defines

the actual high and low temperatures at which the requirements are met.

 For the 64-22 binder, the likely continuous

grade for most binders would be ~ 67 - 25, which indicates there are three degrees of performance “cushion” on the high and low temperature.

 More cushion (especially on LT) = more

• pportunity for recycle in many cases

PG Binder Continuous Grading Examples

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PG Binder Continuous Grading Data

Mix Volumetrics

 Volumetrics make up the basics of everything

done regarding asphalt mix design, production, construction, and performance.

 Critical to understand what mix volumetrics

mean, not just how to calculate using a formula

 Mix designers should work a phase diagram

from start to finish at least once

 Don’t be too proud to review.

Mix Volumetrics – Basic Knowledge, Often Overlooked

Perhaps the most important equation you’ll ever learn!

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HMA Phase Diagram Relationships Asphalt Mixture Compacted Bulk Specific Gravity, Gmb

Mass of agg. and AC

• Vol. agg., AC, air voids

Gmb =

VTotal

aggregate (stone)

Vsb

binder

Vbe air Va VMA

Asphalt Mixture Theoretical Maximum Specific Gravity, Gmm

Mass agg. and AC

• Vol. agg. and AC

Gmm =

aggregate (stone)

Vs

binder Vba

Vb Vmm

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Air Voids, Va

• Calculated using bulk and maximum specific gravities

Air voids (Va) = 100 * Gmm – Gmb Gmm VTotal

aggregate (stone)

Vsb

binder

Vbe

air

Va VMA Voids in Mineral Aggregate (VMA)

• VFA is the percent of VMA that is filled with asphalt

binder (related to “saturation” from soil mechanics)

VFA = 100 x VMA - Va VMA Voids Filled with Asphalt (VFA)

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 How do (should) the commonly used volumetric properties respond to

changes in binder content? What is the sensitivity?

 Volumetrics do not lie when determined correctly!

Basic Volumetric Property Relationships to Binder Content

Binder Content Gmb Gmm Va VMA VFA 3.5 2.370 2.554 7.20 13.70 47.40 4.0 2.394 2.536 5.60 13.27 57.82 4.5 2.410 2.518 4.29 13.15 67.38 5.0 2.418 2.500 3.28 13.32 75.37 5.5 2.412 2.482 2.82 13.99 79.84 6.0 2.403 2.464 2.48 14.76 83.23

Volumetric Property Relationship (Sensitivity)

 As binder increases, the max

gravity of the specimen will decrease due to the binder having a mass less than the aggregate.

 The relationship between Gmm and

binder content is linear.

 Typically, 0.015 to 0.020 per 0.5%

change in binder content.

 This relationship allows the Gmm to

be conducted at one binder content and back calculated with the effective specific gravity at

• ther contents.

Maximum Theoretical Specific Gravity of the Mix, Gmm

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Factors Influencing Volumetric Property Results Factors Influencing Gmb

Factor Effect on Gmb Binder Content Higher binder content increases Gmb up to a point Aggregate Blend Composition Higher specific gravity aggregate (Gse) increases Gmb Compaction Temperature Higher temperatures may increase Gmb Test Procedures Incorrect test procedures utilized could cause varying Gmb Sampling Segregated sample could lead to varying Gmb

Factors Influencing Gmm

Factor Effect on Gmm Binder Content Higher binder content decreases Gmm Aggregate Blend Composition Higher specific gravity aggregate (Gse) increases Gmm (VERY IMPORTANT, Could point to pit/quarry changes and/or segregation) Test Vacuum Pressure Low vacuum pressure decreases Gmm Test Agitation Low agitation decreases Gmm Test Temperature Cooler temperatures increase Gmm slightly Sampling Coarse sample could lead to higher Gmm and vice versa.

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Factors Influencing Binder Content

Factor Effect on Binder Content Aggregate Moisture, % Aggregate moisture higher than plant setting = plant thinks moisture is aggregate and adds too much liquid. Recycled Binder Average and standard deviation of recycled products can swing the total binder content of the mix. 20% RAP w/ 5% average w/ 0.3% standard deviation VS 1% standard deviation. Recycle Feed Rate Consistent rate necessary to achieve consistent total binder content Incorrect Calibration (Plant) Pump, scale, weigh bridge, etc. Poor Sampling / Reduction Coarse sample = lower binder content and vice versa Incorrect Testing Nuclear gauge, extraction, ignition tests not properly conducted

Factor Effect on VMA Aggregate Gradation Dense aggregate blend grading decrease VMA Aggregate Shape Rounded aggregates decrease VMA Aggregate Texture Smooth/polished aggregates decrease VMA Asphalt Absorption Increased asphalt absorption results in lower effective asphalt content and lower VMA (for same compaction level) Dust Content Higher dust contents increase surface area, decrease film thickness and tend to lower VMA Baghouse Fines/Dust Generation Same as above Plant Production Temperature Higher production temperatures decrease asphalt binder viscosity, resulting in more asphalt absorption, lower effective asphalt content and lower VMA HMA Temperature During Paving Higher temperatures during paving increases mix viscosity, resulting in lower air voids and lower VMA Haul Time Longer haul times allow for more asphalt absorption, lower effective asphalt content and lower VMA Aggregate Handling More steps in handling increases potential for degradation, resulting in more fines and lower VMA.

Factors Influencing VMA Impacts: What If’s

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Gradation Impact on Volumetrics

• The maximum density line appears as a straight line from zero to the maximum aggregate size

Understand the Maximum Density Line (MDL)

http://www.pavementinteractive.org/gradation-and-size/

• Grading and VMA
• Move away from Maximum Density

line (in either direction) improves VMA

• Reducing #200 increases VMA
• Coarse graded mixtures require

reducing passing 4.75 to reduce packing to increase VMA

• Fine graded mixture increase #2.36

(although this might increase #200) to increase VMA

• Reducing #200 to the extent D/Be

will allow improves VMA

Grading Impacts on VMA

2/5/2019 20

• A mixture on top of the

maximum density line is finer, and inversely, a mixture below the maximum density line is coarser.

• The VMA will increase as

the gradation moves further from the maximum density line whether coarser or finer.

Grading Impacts on VMA

https://www.uwplatt.edu/files/college-of- ems/HTCP/hma-tpc.pdf

• The cumulative distance (CD) of the

aggregate grading from the maximum density line can be an indication of the VMA in the mix.

• CD is calculated by summing the

absolute differences between the blend grading and the MDL points for each sieve.

• Higher values indicate more space

within the aggregate structure for VMA achievement.

• Value of 0.0 would be a grading

exactly on the MDL.

Grading Impacts on VMA

• Example below illustrates the CD concept for dense graded mixes and SMA
• Notice the high CD for the SMA and the low CD for the “dense – dense” mix (i.e., close to the

MDL)

• Good practice is to plot the CD vs mix volumetrics (i.e., air voids, VMA) to develop

relationship and maximize benefit.

CD Example

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Grading Impacts on VMA

Blend % Passing 12.5 50 5.81 100.0 37.5 5.11 100.0 25 4.26 100.0 19 3.76 100.0 100.0 0.00 12.5 3.12 99.7 82.8 16.92 9.5 2.75 89.0 73.2 15.79 4.75 2.02 69.2 53.6 15.59 2.36 1.47 50.2 39.1 11.07 1.18 1.08 37.0 28.6 8.33 0.6 0.79 26.8 21.1 5.68 0.3 0.58 18.8 15.5 3.35 0.15 0.43 11.6 11.3 0.23 0.075 0.31 5.8 8.3 2.47 0.00 0.0 0.00 79.43 Sieve Size Sieve Size 0.45 MDL % Passing Absolute Difference Cumulative Deviation from MDL (%)

Another Look at VMA

https://www.uwplatt.edu/files/college-of-ems/HTCP/hma-tpc.pdf

• The uncompacted total void space of clean

aggregate (coarse or fine) will be very similar in most cases.

• This results in VMA being able to be

achieved on both the fine and coarse side of the maximum density line.

• Illustration shows a crushed stone aggregate

and sand at varying percentages and the impact on total void space (e.g., uncompacted voids) in the sample without asphalt binder added.

• Void space must be such that the

required air voids are achieved without excessive asphalt binder being required.

Grading Impacts on VMA

https://www.uwplatt.edu/files/college-of- ems/HTCP/hma-tpc.pdf

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Mix Volumetric Property Adjustment

 Need for adjustment is identified.  Questions

1.

Why is the adjustment needed?

2.

What adjustment should be made?

Mix Adjustments Thoughts

Need for Adjustment Identified! What Adjustment(s) Are Needed? WHY are the Adjustments Needed? For example, lowering the P200 by cutting the screenings may help raise air voids, BUT what is the real reason for the P200 increase?

Adjustment Thoughts to Remember

• 1. Know your mixes and their sensitivity to various changes.
• 2. Commonly used rules of thumb for mix adjustment may not be exact for your

mix.

• 3. Base adjustments on all QC testing and inspection data.
• 4. Don't adjust based on 1 test
• Variety of information focused on troubleshooting and adjustment.

Information will be overviewed in the following slides.

2/5/2019 23

General Rules

• f Thumb

NOTES

Gmm Asphalt Binder Gmm Asphalt Binder Gmb Asphalt Binder Gmb Asphalt Binder P200 Air Voids/VMA

1.0% D P200 = 0.3% to 1% D VMA

Asphalt Binder Air Voids

0.1% D AC = 0.25% D Air Voids

Asphalt Binder Air Voids VMA Vbe = VMA - Va Asphalt Binder

• No. 8 x No 200

Air Voids Fine graded mixes Asphalt Binder

• No. 8 x No 200

Air Voids Fine graded mixes Gmb Asphalt Binder P200 Gmb Asphalt Binder P200

THEN IF

0.015 to 0.020 change for 0.5% binder

Major Adjustment Equations

Asphalt / Air Voids Relationship 0.1% D AC = 0.25% D Air Voids Asphalt / VMA Relationship Small D AC = No VMA Effect P200 / VMA Relationship 1.0% D P200 = 0.3% to 1% D VMA (Exact relationship should be determined) P2.36 / VMA Relationship Coarse: + P2.36 = - VMA Fine: + P2.36 = + VMA Notes: 1. General rules of thumb. 2. Basis for initial adjustment. 3. Local relationships needed.

Production and the JMF – What Can Go Wrong? VS

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 One or more of these general areas can drive differences.

1.

Aggregate

2.

Recycle

3.

Binder

4.

Plant

5.

Sampling / Testing

 The key to quality control (mix troubleshooting) is to accurately determine

the cause of the current difference and minimize the frequency and magnitude of future occurrences.

Main Areas That Influence Production Relative to Design

• 1. Stockpile moisture excessive / variable
• 2. Gravities different / variable from design
• 3. Blend water and/or binder absorption

different than design

• 4. Supply inconsistent (grading)
• 5. Segregation (stockpiling and loadout)
• 6. Feed issues at cold feed

Main Aggregate Reasons Driving JMF Adjustment?

 The amount of water falling on a stockpile during a rain event is very

significant.

 Example: 100 ft. x 100 ft. stockpile will collect 26 tons of water

after a 1” rainfall event.

 Highlights the critical need to keep water out of the stockpile!

Stockpile Moisture

Stockpile Footprint (sf) Approximate Dimensions, ft Water Tonnage Over Footprint After Given Rainfall Events (in) 0.5 1 2 3 5000 70 x 70 7 13 26 39 10000 100 x 100 13 26 52 78 15000 125 x 125 20 39 78 117 20000 140 x 140 26 52 104 156 25000 160 x 160 33 65 130 195 30000 175 x 175 39 78 156 234

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 Coarse sand stockpile 24 hr.. after a 2 in. rain

 Moisture varied widely (18 to 4%) throughout 9’ tall

stockpile

 Water retention is maximized with well graded fine

aggregate with high minus 200 content (i.e., screenings)

 Screenings will typically hold more moisture than

manufactured sand

 RAP and RAS stockpiles are also very prone to holding

moisture

 Cover and pave under + slope stockpiles to minimize

moisture.

Stockpile Moisture

 Impact of moisture on plant production rate is

very significant.

 Rule of Thumb:

 1% increase in moisture decreases plant

production by 11 to 13%

 Varies based on other conditions.

 Variable production rate = variable mix

production = variable volumetrics!

Moisture Impact on Production Rate

From: Astec T-129 Stockpiles

 Aggregates have substantial downstream impacts

 Inconsistent grading may/will present problems.  Gradation control and volumetrics  In place density  Pay  Performance

Importance of Aggregates Consistency to Asphalt Mixes

Aggregates must be recognized as a main factor which drives mix success or failure.

2/5/2019 26

• Accuracy is another important term that is
• ften used with precision
• Accuracy refers to how measurements

match the target value.

• Ideal case is high accuracy and high

precision

• Next best case is to have low accuracy

and high precision.

• Bias (difference between process and

target average) can be determined and compensated for during process control.

Accuracy and Precision

Source: http://www.thefreedictionary.com/precision

A Look at Product Variability

• Each mix will have critical sieves
• No. 4, No. 8, No. 200 e.g.
• Understand how aggregate variability impacts these critical sieves
• Variability is of special concern with PWL specs
• The largest clean stone product variability will be 1 to 2 sieves below the top

POOR

What are Acceptable Levels of Variability?

• Do you know your typical variability for key properties?

Property Acceptable Standard Deviation ? Asphalt Content < 0.15 to 0.20 % Coarse aggregate (+No. 4 blend) < 2 % Fine aggregate (- No. 4 blend) < 1 to 1.5 % P200 (blend) < 0.5 % Air voids and VMA < 0.3 to 0.4 % Field density < 1.0 to 1.5 % Film thickness < 0.50 microns 2016 World of Asphalt Mix Optimization Fundamentals “Acceptable” May Vary for Different Situations

2/5/2019 27

 MUST prevent

segregation of material when stockpiling and loadout!

Segregation

Good Stockpile (Gravel)

Zones of Segregation in a Conical Stockpile

 Loadout from a Conical Stockpile

 Approach perpendicular to conveyor  Apply the “Rule of Thirds”  Left, center, right loading  Insert bucket above the group (~1ft) to minimize

moisture and contamination/segregation

 Roll bucket up while scooping through overlying

layers to minimize disturbance of the stockpile

Loader Techniques to Minimize Segregation

From: Florida DOT

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 Incorrectly calibrated cold feed bin feed or weigh bridge can result in substantial errors.  Properly calibration procedures must be utilized on a routine basis.

Incorrect or Inconsistent Aggregate / Recycle Supply

• 1. Binder different than design (even though using the

“same” PG)

• 2. Variable binder addition

Main Asphalt Binder Reasons Driving JMF Adjustment?

 Crude sources used for binder manufacture

are constantly changing.

 Two binders with the same PG classification

can act differently.

 Must obtain a true PG classification from the

binder manufacturer to help ensure consistent source from production relative to design.

 If possible, test the binder to check

characteristics.

 This is especially critical when using recycled

materials to help ensure the desired composite blended binder grade is achieved.

Binder Differs From Design

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 Asphalt binder addition errors can be caused by a multitude of

reasons.

 Plant operator error  Incorrect asphalt pump operation / calibration  Weighing issues on conveyor  Incorrect adjustment for aggregate moisture  Incorrect asphalt binder content in the recycled materials

utilized

Variable Binder Addition

 The plant moisture setting (PMS) should match the actual moisture

content (AMC) of the aggregate/recycle blend.

 IF the actual moisture content is greater than the plant moisture

setting…

 Plant thinks the difference is aggregate and adds too much binder

 IF the actual moisture content is lower than the plant moisture setting…

 Plant thinks the difference is moisture and adds too little binder

 Too little or too much binder will result in volumetric property

differences and cost issues!

Plant Moisture Setting and Actual Moisture Content

 When making plant binder contents adjustments for moisture, it is a good idea to make small

(e.g., 0.1%) incremental adjustments and allow the plant production to “settle in” (e.g., run 50 tons) prior to testing.

Binder Adjustment Comment

2/5/2019 30

 Accurate binder content is required for the recycled products.  Design value must be the “true” stockpile value!  Use caution if stockpiles are added to or modified from design to

production.

 Assume 30% RAP in a mix

 Design RAP binder content used = 5.0%  Binder from RAP = 0.30 (5.0) = 1.5%  Actual Stockpile RAP = 4.5%  Error in virgin binder addition = (4.5 – 5.0) x 0.30 = - 0.15%

(too little binder added, dry mix issues)

 Proper recycled stockpile process control is a MUST!

Incorrect Recycled Materials Binder Content

Plant Issues

1.

Binder pump not operating correctly/not calibrated

2.

Cold feed not calibrated

3.

Weigh bridge not calibrated

4.

Moisture not properly accounted for

5.

Poor dust control

6.

Production temperature too hot / too cold

7.

Inconsistent storage time

8.

Excessive mix switchovers

9.

Variable production rate

Main Plant Reasons Driving JMF Adjustment?

Covered in aggregates and binder Plant operation related factors

2/5/2019 31

 Some or all collected dust is often returned back to

the aggregate prior to mixing.

 Consistency in the “collection” and “return” of the dust

is key to a consistent aggregate grading and volumetric properties.

 If the collected dust is returned, the mix gradation will

be “approximately the same” as the grading of the new aggregate/recycle.

 If the dust is wasted, the grading will likely differ

substantially.

 On occasion, the dust will be wasted to some degree

to compensate for dust generation during production.

Poor Dust Control

 Production of a single mix for the entire day highly desirable, but generally unrealistic, for

consistency considerations.

 Issues are mainly a concern with continuous mix (drum) facilities where the mix is changed “on

the fly”.

 Tips

 Maximize the production runs of a particular mix to limit the number of mix switchovers during

the day.

 Minimize / consolidate (if possible) the number of mixes produced in a particular plant. This is

especially critical for high profile mixes with stringent acceptance requirements/specifications (e.g., interstate SMA project).

 Avoid having the plant serve as a “grocery store” or “cafeteria”.  Communicate with customers to let them know about similar mixes for their applications.

Excessive Mix Switchovers

 A production temperature that is too hot, too cold, or hot / cold

(variable) will result in volumetric property and construction issues.

 Too hot

 Increased binder absorption  Increase binder aging  Decreased effective binder (high voids, high VMA, high dust / Pbe)  Difficult compaction due to less effective binder present

 Too cold

 Inadequate coating  Inadequate blending of recycled binder  Decreased binder absorption  Difficult compaction due to temperature

Variable Production Temperature

2/5/2019 32

Temperature and Storage Time Impacts

• Production temperature and

storage time can impact binder absorption and Gmm

• Result can be significant to

volumetrics.

• Gse
• Gmm
• Va
• VMA
• VFA
• EVERYTHING!!!!
• MUST be aware of the impact
• f binder absorption vs time.

Mix Production Temperature and Storage Time Impact Mix Aging Impact on Absorbed Binder

Hours Hours http://mdot.ms.gov/documents/research/Reports/Interim%20and%20Final%20Reports/State%20Study %20245%20Aggregate%20Absorption%20in%20HMA%20Mixtures.pdf

2/5/2019 33

• A HMA

mixture has total asphalt content of 6.0 percent with a Gmm of 2.500 prior to aging. After aging, the Gmm is 2.520.

• How much

additional binder absorption has

• ccurred?

Mix Production Temperature and Storage Time Impact on Gmm

 A production rate that is high / low can result a variety of mix issues.  Too high

 Decrease aggregate / recycle drying  Increased moisture in the aggregate / recycle  Potential for asphalt binder content errors due to aggregate / recycle

moisture differences

 Potential for variable dust return  Potential for cold feed variability

 Too low

 Potential for variable dust return  Potential for cold feed variability

Variable Production Rates

Sample, Process, and Test

2/5/2019 34

 Evaluate the quality of an asphalt mix  Control product at supply source  Control operations at site of use  Acceptance or rejection of the materials  REMEMBER:  Proper Sampling is the first step of testing any

product

 Quality of the sample = Quality of the test result!

Importance of Sampling

http://apiland.net/asphalt-plants/

 Obtaining the sample is only the first step in

• btaining an accurate test result.

 Must reduce the obtained sample to a

smaller size for testing.

 How do we reduce the sample size?  Several methods available

 Splitting  Quartering

Process the Sample Correctly

 Test methods are developed to provide a standard

practice for conducting a particular test method which generate a test result.

 Methods must be followed for the test result(s) to be

meaningful.

 AVOID…

1.

Taking shortcuts

2.

Playing the tolerance game

3.

Utilizing alternate interpretations of how to run the test

4.

BEING LAZY!

Run the Test Correctly in Accordance with the Governing Standard

2/5/2019 35

Mix Optimization Using Performance Tests

PERFORMANCE

Rutting Tests

Hamburg Wheel Test (HWT) Asphalt Pavement Analyzer (APA) AMPT Dynamic Modulus

Cracking Tests

Bending Beam Fatigue Texas Overlay Test SCB

• LTRC – Jc
• IFIT

Direct Tension Cyclic Fatigue, S-VECD Disc Shaped Compact Tension (DCT)

2/5/2019 36

 “Optimization is an act, process, or

methodology of making something (as a design, system, or decision) as fully perfect, functional, or effective as possible.”

What Exactly is Optimization?

https://www.merriam-webster.com

Optimizing Mixtures: Some Questions to Ask

 Without a governing specification, what would I like to use in my mix?

 More recycle, alternate aggregates, different grading, different binder,

rejuvenator, different NMAS?

 What materials do I have that would separate me from the competition?

 Capped aggregate products, internal binder supply, surplus recycle, etc.  These items should be those that have the most potential economic benefit;

performance will have to be achieved!

 Can mixtures with these materials be produced and constructed

consistently?

 What is the total economics of the mix design + production + construction?  Penalties may offset materials savings.

 How can I better understand cause and effect of mix variables?

Effective Optimization

 “Un-necessary” gains in

performance can offset savings.

 Meet the required

performance while considering variability, but don’t over design.

2/5/2019 37

Key Points to Remember

 DO NOT ASSUME ANYTHING!  Use extreme caution when trying to “correlate” or make

assumptions about mix performance in one test to another.

 For example, IFIT vs DCT

 Different test evaluate different aspects of the mix.

 One may be binder sensitive, while another may be

aggregate sensitive.

 Test results may be in the same “direction”, but may not be

directly proportional.

http://www.itinthed.com

Performance Space Diagrams

• Performance

testing within a BMD allows an improved visualization of mix performance relative to economics.

• Allows for

effective mix

• ptimization!

Example Data for Illustration Purposes

Balanced Mix Design

Better Cracking Performance Better Rutting Performance

Good Performance

2/5/2019 38

Test YOUR Mixtures to Gain Knowledge

Category Mix Factor Factor Direction Mix Impact Impact on Rutting Impact on Cracking Angularity More Angularity Increase mix shear resistance (internal friction) Less Varies Particle Shape More Cubical Increase mix shear resistance (internal friction) less Varies Surface Texture More Texture Increase mix shear resistance (internal friction) Less More Absorption Higher Absorption Varies based on effective binder content Varies Varies Hardness Harder Increase mix shear resistance (less breakdown) More Less Blend Grading Coarser Varies based on other properties Varies Varies RAP More RAP Increased binder stiffness / mix stiffness Less More RAS More RAS Increased binder stiffness / mix stiffness Less More Total Binder Content Higher Decrease mix stiffness More Less Effective Binder Content Higher Decrease mix stiffness More Less PG Binder High Temp Higher Increase binder stiffness / mix stiffness Less Varies PG Binder Low Temp Higher Increase binder stiffness / mix stiffness Varies Less Air Voids Higher Increase mix stiffness, less effective binder Less More VMA Higher Decrease mix stiffness (for same air voids) More Less D/Pbe Higher Increase mix stiffness Less More VFA Higher Increased effective binder More Less Polymers Higher Dosage Increase binder stiffness/elasticity Less Less Asphalt Rubber Higher Dosage Increase binder stiffness/elasticity Less Less Binder Additives Aggregate Recycle Volumetrics

Put a Number to These

Cost + Performance + Risk: Three Key Parameters!

 Key Parameters to Accurately Understand and Conduct Mix Optimization

 Cost  Performance  Baseline or differential performance  Risk  What is the increased risk (if any) taken on with the alternate mixes?  Analysis  Baseline: How much does it cost for a mix to meet the required performance?  Materials cost for baseline mix performance is $30.00  Differential: How much does it cost to move a mix to acceptable performance?  Example: Cost is $1.50 per ton more to move mix performance from one level to another with

minimal increase in risk (i.e., penalties).

Performance

Questions

http://www.pennyauctionwatch.com/

Shane Buchanan Asphalt Performance Manager, Oldcastle Materials 205-873-3316 sbuchanan@oldcastlematerials.com

2/5/2019 39

Thank You

Session Evaluations/PDH’s

• Complete session feedback in

mobile app, your comments appreciated.

• Professional Development

Hours logged in session feedback.

See you again at:

• CONEXPO-CON/AGG 2020

– March 10-14, 2020 – Las Vegas, NV – 140+ education sessions

• World of Asphalt 2021

– March 16-18, 2021 – Atlanta, GA – 120+ education sessions

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