mix optimization fundamentals - mys · 2016 world of asphalt mix optimization fundamentals ymix is...

W O R L D O F A S P H A LT

N A S H V I L L E , T E N N E S S E E

M A R C H 2 4 , 2 0 1 6S H A N E B U C H A N A N , O L D C A S T L E M AT E R I A L S

Mix Optimization Fundamentals

Importance of mix optimizationMix optimization areasFundamental mix propertiesAggregate variability impactEffective utilization of recycled materialsCommunication

Session Focus and Discussion Items

2016 World of Asphalt Mix Optimization Fundamentals

Understand the total picture concept of mix design so that optimization can take placeUnderstand the importance of aggregate consistency on qualityManage recycled products to ensure optimum addition levels and benefitsUnderstand obstacles to mix optimization and how to overcome them

Session Takeaways


Optimization Importance and Value


Designing an optimized mix can help separate yourself from competition and ensure competitivenessFor example: 0.1% liquid asphalt binder has impact of ~$0.55 per mix ton ($550 / ton AC)

Contribution of liquid asphalt binder to total mix cost has increased dramatically

Mix Optimization Represents Significant Opportunity


AC is 65 to 70% of Material Cost

Asphalt Binder Price Trend

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Mix optimization represents a huge opportunity (one that must not be passed up)• Reducing the virgin liquid demand by 0.1%

0.001 x $300 to $550 per ton liquid / ton x 45 M tons = $15,750,000 to $24,750,000

• Reducing production cost (e.g., lower cost materials, lower energy, etc.) by $0.01

$450,000

You MUST focus on saving pennies any way possible• "If you look after the pennies, the dollars will look after

themselves."-J. Paul Getty

Mix Optimization Should be Important to YOU!


Mix Design


Remember both Performance and EconomicsWhat are the specifications?What aggregates are available?What asphalt binder is available?What does past experience provide?Did some mixes work better than others?

What is Mix Design?


"Boonsborough Turnpike Road" between Hagerstown and Boonsboro, Maryland in 1823.

Mix Design is a Balance (3 legged stool)Materials SelectionProducability Constructability

You must not design a mix in a vacuum!Get input from production and construction personnelKnow the cost of mix componentsConduct mix audits to understand what worked and what didn’t

Decision RedesignAcceptTweak

The Mix Design Cycle


Depends on how we define “Good Quality”.Good Quality is not defined by any one of these factors

CheapExpensiveQuickHigh binder replacementConstructible / workablePenalty freeConsistent

A “Good Quality” mix must be at least partially defined as one that meets the requirements of the job (specification compliance consistency and performance) intended performance while being designed using an optimized approach.

What is a “Good Quality” Mix Design?


Pendulum of Asphalt Mix Performance


DRY WET

OPT

IMU

M

Mix Optimization Path


Understand the fundamentals of asphalt mixes and know what drives economics and performanceTake a fresh look at mixes to locate potential for unrealized economic and performance gains

Having done things the same way for many years is not an excuse for not trying to improve

Emphasize the need for clear communication between mix designers and management

Quality control personnel should be engaged with the business process

Be involved and make recommendationsIt’s quality “control”, not quality “monitoring”.Take action. Don’t wait until the problem happens before your voice is heard!

Key Concepts in Mix Optimization


Perform Critical Review of Historical Mixes

Review the design, production and construction of historical mixesThoughts:

Identify successful mixes (maximized profitability, minimized cost, good producability and constructability).Tweak existing mixes to increase success.Eliminate the mixes with significant issues.Design new mixes based on past successful performing mixes

Don’t re-invent the wheel (they are always round!)Don’t stop trying to advance the ball forward!

Opportunity that exists must be acted upon.


Important things need to get in the mix design before less important things take up all the optimization opportunity

Big Rocks and Little RocksBig rocks may be recycle, capped aggregates, alternate aggregate products, etc.Little rocks are other materials that are necessary, but may limit the big rocks.

Get the Important Items in the Design First


Source: http://greenertrees.net/2012/09/16/big-rocks-and-veggie-tales/

Optimization Ideas to Maximize Success


1. Be up to date on specifications. Has something changed that could make for a more economical mix?

2. Review mix volumetrics to “make sure you know what you think you know”.3. Take advantage of lost opportunities to utilize capped products (internal and external sources).

4. Use the lowest absorption aggregates possible. Consider total cost of use (aggregate, drying, transportation, etc.).

5. Accurately determine aggregate specific gravities and maximize higher specific gravity aggregate use.

6. Investigate the gradation/property variability of used aggregates. “Saving a nickel and losing a dime is not a good deal”

7. Understand the impact of aggregate properties and blend grading on asphalt content and mix volumetrics.

8. Manage recycle products to ensure optimum addition levels and economic benefit

9. Avoid pressure from construction to increase asphalt content of mixes to help obtain density. Evaluate other options (temperature, rollers, aggregate structure, etc.)

10. Learn to effectively communicate within your company and to outside suppliers/customers to overcome potential obstacles.

Mix engineering is a continuous improvement process, not just a one time look!

Ideas on Mix Optimization


Make sure you know the target so you can maximize opportunities

DO NOT leave opportunity on the tableYou might fail to maximize opportunities, but you must tryWhat are the current specifications?

Have special provisions been created?Blanket or job specific SP?

Be actively involved in association/DOT liaison activitiesUnderstand the specifications better than the person who wrote them!

Be Up to Date on Specifications!


“Make sure you know what you think you know”“Never be too proud to ask questions”

Pride and ego will lead to $ lostWhat are volumetric properties?

Volume based/determined properties

Mix Volumetrics – Review of the Basics


HMA Volumetrics (Basic Knowledge, Often Overlooked)


Mix is air, asphalt, and aggregateEverything during mix design comes back to the very basics of this diagramCritical to understand what mix volumetrics mean, not just how to calculate using a formulaMix designers should work a phase diagram from start to finish at least once

GGGmbbbbb = 2.329

air

asphaltasGGGb

sphaltasb = 1.015

PPPb

GGb 1.015Gb = 5% by mix

aggregateGsb = 2.705Gse = 2.731

absorbed asphalt

VOL (cmmm3 mm3 3 ) MASS (g)

1.000 pores not filled w/ ac

2016 World of Asphalt Mix

air

asphaltasGGGb

sphaltasb = 1.015

aggregateGsb = 2.705Gse = 2.731

absorbed asphalt2.3291.000

0

0.108

0.008

0.116

2.213

0.182

VOL (cmm3 m3 ) MASS (g)

0.818

0.076

0.10600.114

0.810

0.008

Air Voids = 7.6% Effective Asphalt Content = 4.6%Aiir Voids 7.66%VMA = 18.2 %

pEffective Asphalt Conntent 4.6%%Absorbed Asphalt Content = 0.4%VMMA 18.2 %%

VFA = 58.2 %Absorbedd Asphalt Coontent Max Theo Sp Grav = 2.521

pores not filled w/ ac

2016 World of Asphalt Mix

VMA: Understand What It Means, Not Just How to Calculate ItVMA is the volume of air voids and effective binder (binder not absorbed into the aggregate)Excludes the portion of binder absorbed into the aggregateVolume air = 0.076 cm3

Volume effective AC = 0.106 cm3

Volume total = 1 cm3


VMA = ((0.076 + 0.106) / 1) x 100 = 18.2%

Plotting VMA in Mix Design

The optimum binder content of a mix is normally located near the bottom of the VMA vs binder content curve.Why does the curve have this shape?

Binder initially acts as a lubricant which aids in aggregate packing to a maximum state. Afterwards, excess binder acts to push the aggregate apart resulting in a lower density.


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


Aggregate Grading Impact on VMA

Think of VMA as the void space in the aggregate blend

With AV constant, VMA is tied directly to AC%Fill the space in the most economical manner possible while maintaining performance

Move away from Maximum Density line (in either direction) increases VMA Reducing No. 200 increases VMAFor 9.5 and 12.5 NMS mixes, the minus No. 8 is especially critical

Decrease for coarse graded mixesIncrease for fine graded mixes


Depends on many factors includingVMA minimum specification, VMA control during production, VMA as pay item, historical VMA production “collapse”, aggregate Gsb variability impacts, VMA production variability

The decision should be made locally, BUT it should be well thought out and documented.Generally 0.3 to 0.7% VMA is lost during production.

Very dependent on breakdown potential of aggregates

If you are paid on VMA, use historical VMA variability to minimize the amount of extra VMA targeted for during designStrongly suggest reviewing VMA requirements

through statistical measures.

Mix Nominal Max Size Minimum VMA, %

4.75 16.0

9.5 15.0

12.5 14.0

19.0 13.0

25.0 12.0

37.5 11.0

AASHTO M323

REMEMBER: Every 0.25% of unnecessary VMA results in $0.50 (w/ $500 / ton liquid) of unnecessary mix cost!

Determine How Much VMA is Needed


Asphalt Content Can Be Estimated

Phase relationships can be used to back out the estimated asphalt content for the mixGiven

Aggregate blend percentages with associated specific gravities (% aggregate solid volumes; bulk, effective, and apparent)Required air voids (% of total volume)Required voids in mineral aggregate (VMA)

Base this value on historical VMA collapse during production (e.g., VMA design + 0.7% during production)If you are paid on VMA, use historical VMA variability to minimize the amount of extra VMA targeted for during design


Properties ValuesAggregate Blend Gsa 2.725Aggregate Blend Gsb 2.684Blend Water Absorption, % 0.56Estimated Asphalt Absorption, % 0.29Aggregate Blend Gse 2.705Assumed Trial AC, % 5.00Volume Solid Apparent (Vsa), ml 34.86Volume Solid Bulk (Vsb), ml 35.39Volume Solid Effective (Vse), ml 35.12Air Voids, % 4.00VMA, % 16.00Volume Asphalt Absorbed (Vac abs), ml 0.28Mass Asphalt Absorbed (Mac abs), g 0.28Percent Binder Absorbed (Pba) 0.30Percent Binder Effective (Pbe) 4.70Volume Binder Effective (Vbe), ml 4.59Volume Binder Total (Vbt), ml 4.88Volume Total Mix (Vt), ml 41.66Volume Air Voids (Va), ml 1.67Va + Vbe, ml 6.25VMA ((Va+Vbe / Vt)*100) 15.01VMA (Design - Actual) 0.99Estimated AC% to Achieve Design VMA, % 0.50

Adjusted AC to Achieve Target VMA 5.48New Pbe 5.18New Vbe 5.06New Vbt 5.35New Vt 42.15New Va 1.69New Va + Vbe 6.74Target VMA (% of total mix check) 16.00

Asphalt Mix Rules of Thumb

0.1% ∆ Asphalt Content = ~0.25% ∆ VMACoarse mixes have greater sensitivity to AC% than finer graded mixes

1.0% ∆ P200 = 0.3% to 1% ∆ Air Voids and VMAIncreased distance away from the maximum density line (0.45 power curve) yields more void space

This space will be either air or asphalt


Aggregate Items


Capped products have been “written off the books”Using these products can potentially reduce materials costsApplicable for externally or internally supplied products

Examples: Screenings, manufactured sand

Test to ensure quality is presentGood fit for 9.5 or 4.75 mm mixes Must balance with needed RAP use

RAP replaces “fines” at a 90% levelFine fractionated RAP replaces at 100%

Utilize Surplus or Capped Products When Possible


Cautions:1. Make sure the materials perform

appropriately in the design. 2. Do not be “guilted” into using capped

products!3. Make sure sufficient quantities exist for

the job(s).

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)


Apparent Specific Gravity, Gsa


Bulk Specific Gravity, Gsb


Effective Specific Gravity, Gse


FHWA RAP Expert Task Group

Gse is an aggregate propertyFor a given mix design, the relationship between Gse to Gsa and Gsbshould 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.

Monitoring Gse During Production


Aggregate Gravity Control Chart

Maximizing Success: Monitor Gse


Impact of Aggregate Specific Gravity


Understand the impact of changing specific gravity

Variable gravities will impact volumetricsChanging aggregate gravities can impact binder volume in the mix

Heavy aggregate relative to design = higher binder volume (and vice versa)0.1 Gsb ∆ = 0.2% AC ∆

Do your gravities change around your quarry/pit? Probably!

How much?0.01 Gsb ∆ = 0.3% VMA ∆

Beware of Fine Aggregate Specific Gravity Issues!

With some aggregates, the accurate determination of SSD with the cone test is difficultAngularity and high fines content may make the fine aggregate appear wetter than actualResult is the sample being dried past the true SSD condition

Absorption too high and Gsb too low VMA issues may result

If possible (allowed), wash the fine aggregate over the No. 200 sieve prior to testing


http://pavementinteractive.org/index.php?title=Image:No_slump.jpg

NCHRP 4-35 Project (Report 805)


Using Low Absorption Aggregates


When possible try to use the lowest absorption aggregates as possibleNegative impacts of high absorption are widespread

AC absorptionDrying costsMix production decreaseMix production variability

Dry aggregates vs wet aggregates

Absorption of “x”% does not mean the same for all aggregates

Pore space is the keyLarger pore space allows the aggregate to drain/dry more efficiently

Using Low Absorption Aggregates - $ Impact


Asphalt absorbed into surface pores is non-effective (“wasted”).Example:

Agg. 1 = 1.5% absorptionAgg. 2 = 1.0% absorptionAssume asphalt absorption = 50% of water absorption.Additional cost for using Agg. 1 = 0.0025 * $550 per ton asphalt

$1.4 per mix ton

Caution: Do not use WMA just to try and lower AC.

Hidden Cost of Aggregates - Moisture


How much water are you buying?Moisture content is water weight / solid aggregate weight

How much does it cost to dry the aggregate?$ / dry ton = ($ / wet ton) x (1 + w / 100)Example

5,000 tons of W10’s purchased from a quarry at $18.00 / ton with 5.6% moisture at delivery$ / dry ton = ($18.00 / ton) x (1 + 5.6/100)

= $18.78Dry inventory = 5,000 tons / (1 + w/100)

= 4,734 tons

More on Moisture……


Typical rules of thumb“The 1-11-11 Rule”1% increase in aggregate moisture content increases the plant drying cost by 11%1% increase in aggregate moisture decreases plant production rate by 11%

Example: Aggregate blend has 5% total moisture after rain with plant production normally at 400 tph with aggregates at 2% moisture.

Increased cost to dry aggregate = (5 - 2%) x 11% = 33%Production rate decrease with “wet aggregate” = 3% x 11% = 33% x 400 tph = 132 tph decrease down to 268 tph.

http://www.bing.com/maps/default.aspx?q=6701+E+Hanna+Ave+Tampa%2c+FL+33610&mkt=en&FORM=HDRSC4

Aggregate Consistency and Quality

The standard deviation is an indication in the “spread” of the data Data falls within the normal distribution 68, 95, 99.7% Use statistics to optimize your operations (i.e. just the right amount of safety factor)

Take Time to Understand Basic Statistics and Use Them to Your Advantage


Aggregates have substantial downstream impacts

Inconsistent supply may/willpresent problems.

Gradation control and volumetrics In place densityPay Performance

Importance of Aggregates to Asphalt Mixes

Aggregate Quality Analysis Pilot

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

An asphalt producer needs an aggregate product that is produced using a highly capable process.

Capable process is defined byAccuracy: Production grading is close to the target which the asphalt producer used to design their mixesPrecision: Production grading variability is as low as possible.

Just being within spec is generally not good enoughGoal IS NOT to just keep the bowling ball out of the gutter

Low precision + High variabilityGoal IS to target a strike with every roll

High precision + Low variability

Importance of Aggregates to Asphalt Mixes

Aggregate Quality Analysis Pilot

You MUST know and understand the gradation variability of available aggregatesInconsistent supply WILL impact mix grading and volumetricsAccurate and precise aggregate grading

Accurate means the average remains near where the mix design was developedPrecise means the standard deviation (variability) is small

You can work with a grading that is at the high or low side of a target size grading

Example: Either coarse or fine 78’s are OK, BUT, don’t give me coarse 78’s one day and fine 78’s the next!

Pay attention to aggregate facilitiesDoes varying the plant production modes impact product grading or shape?

Different crusher loads have substantial impact

Investigate the Production Variability of Available Aggregates


Accuracy (Avg.) and Precision (Std. Dev.)


A Look at Product Variability

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• 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

Another Look at Product Variability

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GOOD

• Aggregate plant operational factors drive variability (good and bad)• Modes• Fines processing (screw, air)• Primary product focus for sales

• Most plants yield roughly 1/3 clean stone, 1/3 base, and 1/3 fines• However, primary products will dictate other products

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


“Acceptable” May Vary for Different Situations

1. Define what is excessive variability?Investigate individual product variability with typical mixesDetermine critical sieves and products

2. Request historical data from supplier3. Address excessive variability issues with the aggregate supplier

Sometimes this is YOU! 4. Start/maintain effective communication with aggregate supplier5. Recognize that you can affect variability after obtaining from aggregate supplier

Proper stockpiling / loading techniques must be maintained6. Use available tools to evaluate variability

Excel, Stonemont QC, , etc.

What Should You Do to Help Maximize Success?


Clearly establish the problem: Stonemont Product EvaluationGood, but doesn’t show trends

Maximizing Success – Stonemont Product Evaluation


Stonemont Run or Control Charts to Illustrate Changes Over TimeSame information as with product evaluation, but trends can be easily identified

Maximizing Success – Stonemont Control Chart


Variability IllustratorDetermine the sensitivity of PWS to production average and standard deviation.Results can be used to show 1) the impact of current production and 2) how production can be improved

Maximizing Success: Variability Illustrator

Average % Passing 55Standard Deviation, % 4 95.4 0.01 1 2 3 4 5 6 7 8 9 10Upper Spec Limit (USL) 63 46.0 0.0 15.9 30.9 36.9 40.1 42.0 43.2 43.6 43.3 42.6 41.6Lower Spec Limit (LSL) 47 47.0 50.0 50.0 50.0 50.0 50.0 49.9 49.6 48.9 47.7 46.2 44.5Avg. + (2*Std. Dev.) 63 48.0 100.0 84.1 69.1 63.1 59.9 57.8 56.0 54.1 51.9 49.6 47.3Avg. - (2*Std. Dev.) 47 49.0 100.0 97.7 84.1 74.8 69.1 65.3 62.1 59.0 55.9 52.8 49.9Abs Deviation from Mid-Target Band 0 50.0 100.0 99.9 93.3 84.1 77.3 72.1 67.6 63.4 59.4 55.6 52.1% Above USL 2.28 51.0 100.0 100.0 97.7 90.9 84.0 78.0 72.5 67.3 62.5 58.0 54.0% Below LSL 2.28 52.0 100.0 100.0 99.4 95.2 89.1 82.7 76.4 70.4 64.9 60.0 55.6Percent Within Specification 95.4 53.0 100.0 100.0 99.9 97.7 92.7 86.2 79.4 72.8 66.8 61.4 56.7

54.0 100.0 100.0 100.0 98.9 94.8 88.3 81.2 74.2 67.9 62.3 57.455.0 100.0 100.0 100.0 99.2 95.4 89.0 81.8 74.7 68.3 62.6 57.656.0 100.0 100.0 100.0 98.9 94.8 88.3 81.2 74.2 67.9 62.3 57.457.0 100.0 100.0 99.9 97.7 92.7 86.2 79.4 72.8 66.8 61.4 56.758.0 100.0 100.0 99.4 95.2 89.1 82.7 76.4 70.4 64.9 60.0 55.659.0 100.0 100.0 97.7 90.9 84.0 78.0 72.5 67.3 62.5 58.0 54.060.0 100.0 99.9 93.3 84.1 77.3 72.1 67.6 63.4 59.4 55.6 52.161.0 100.0 97.7 84.1 74.8 69.1 65.3 62.1 59.0 55.9 52.8 49.962.0 100.0 84.1 69.1 63.1 59.9 57.8 56.0 54.1 51.9 49.6 47.363.0 50.0 50.0 50.0 50.0 50.0 49.9 49.6 48.9 47.7 46.2 44.564.0 0.0 15.9 30.9 36.9 40.1 42.0 43.2 43.6 43.3 42.6 41.6

Variability Illustrator

INPU

TCA

LCU

LATE

D

Standard Deviation

Aver

age

Perc

ent P

assi

ng

PWSPercent Within Specification ("What If") Table

Click to Update Table


Variability Illustrator, cont.Question: What is the maximum variability and still maintain a desired PWS?

Answer: Function of proximity of production average to mid band grading and gradation band width.

Maximizing Success: Variability Illustrator


Production averages differing from band mean will result in less PWS for a given band tolerance. Use these data as guidance to improve your process.

Aggregate blends are very seldom truly optimizedAggregate cost is more that just $”x” per ton!

Must consider the total picture when evaluating blendsBlending involves more than just getting a blend to meet the specification points.Total picture includes aggregate product availability, moisture, asphalt absorption, and variability of grading

Must move beyond a “deterministic” approach into a “probabilistic” approach, which considers variability and offers the ability to evaluate risk.

Stop blending just based on average gradingSuccessful contractors will understand statistics and use them to their advantage!

Don’t be blind to the total cost of aggregate ownership

Maximizing Success: Aggregate Blending


FHWA RAP Expert Task Group

Aggregate cost is more that just $”x”per ton!Cost components of aggregate

Material (solid + moisture)TransportDrying energyAsphalt absorptionAsphalt plant productionConsistency and impact ondownstream performance / pay!

Aggregate Blend Total Cost of Ownership


Recycled Products


Manage and Utilize Recycle Products for Maximum Return


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

Manage and Utilize Recycle Products for Maximum Return


Let’s go back to the “How much can you use?” questionWhat allowed by the specifications?What capable by the plant?

Plant type (batch, parallel flow, counter flow, etc.)How many recycle bins?

Using RAP only, RAS only, or RAP+RAS?Keep SAFETY in mind always (e.g., high RAP + clogged feeder = problems)

Maximize opportunity with regards to specifications/production/laydown

Estimated Value of Recycle Products

0.270.35

0.42

0.60

0.80

1.00

0.360.47

0.58

0.98

1.28

1.58

0

0.2

0.4

0.6

0.8

1

1.2

1.4

1.6

1.8

RecycleAC, %

3.5 5.0 6.5 15.0 19.0 23.0 3.5 5.0 6.5 15.0 19.0 23.0

Recycle RAP RAS RAP RAS

AC, $ 500 750

Savi

ngs (

$ pe

r Ton

for E

ach

% R

ecyc

le U

sed)

Assumptions: $5 per ton RAP cost, $15 per ton RAS cost, $10 per ton aggregate cost


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

What Type of RAP Do You Have?


Take Time to Analysis RAP (Especially Grading)


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


So What are Acceptable RAP Property Tolerances?


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


NCAT study evaluated 74 RAP stockpiles in 14 states, and 60 virgin aggregate stockpiles in 6 statesRAP would found to have lower grading variability

Is this surprising? Probably not, RAP has been sized and processed more than virgin aggregateIs it always the case? No, but likely

What is your case?

Fractionated RAP is Not Always More Consistent


NCAT RAP Study Data (fractionated vs unfractionated RAP)

Utilize RAP Fractionation When Beneficial


Evaluate the Blended Binder (Virgin + Recycled)

It is critical to understand the blending of virgin and recycled binders.Blended binders (stiff recycle binder + softer virgin binder) are likely to have a higher “high temp” grade and a higher “low temp” grade.

PG 64-22 may become a PG 70-28MUST understand that the RAP binder and RAS binder are NOT the same!

20% binder replacement from RAP and RAS differEvaluate desired blends of RAP and RAS to determine the impact on the composite PG grade.


Binder Blending Analysis Steps

Determine the binder contents of the RAP and/or RAS.Determine the continuous PG grade for the virgin, RAP and/or RAS binders.

What does continuous PG grade mean?PG 64-22 ~ PG 67.5 – 25.5 for example.

Ask binder supplier for virgin PG grading (should be readily available)Different binders have varying levels of “cushion” on the high and low ends.

Based on feedstock and refining process.Sample recycle and determine the average continuous PG grade

Two to three samples per recycle product


Recycled Material – Blending CalculationBlending equations can be used to estimate the allowed RAS or RAP (in this case) to maintain the desired final PG performance.Tblend = temperature requirement for final blend of RAP AC and virgin ACTvirgin = critical temperature for virgin asphalt binderTrap = critical temperature (high or low) of the RAP binder determined fromextraction, recovery, and PG grading.

Tblend – TvirginTrap – Tvirgin%RAP =


Recycled Material – Example Blending CalculationGiven:

Desire to maintain a -22C low temperature through the use of a PG 58-28 binder (i.e., a PG binder bump from -22 to a -28).Tblend = -22.0Tvirgin = -28.7 (from testing of virgin PG 58-28 binder)Trap = -11.1 (from extraction/recover of RAP binder)Maximum %RAP allowed to maintain -22C temperature using a PG 58-28 virgin binder is 38.1%

-22.0 – (-28.7)-11.1 – (-28.7) %RAP = = 38.1%


Develop a blending program which quickly shows the allowable recycle addition to meet the end results PG binder requirements.Use this for better selection of virgin PG grades and recycle loading

Blending Analysis

AAPT 2016

100.05.115

415.016.031.0

48.451.6

33.25PASS

Achieved PG Low Temperature, C -16.5Desired PG Low Temperature, C -16.0

Pass or Fail

BINDER BLENDING ANALYSIS

% BR from RAS% BR Total (Actual)% of Total BR from RAP% of Total BR from RAS% BR Total (Allowable)

Maximum % RAP Allowed (100% RAP BR)Maximum % RAS Allowed (100% RAS BR)Desired % RAP (Weight of Total Mix)Desired % RAS (Weight of Total Mix)% BR from RAP

Pass

Fail

The Roadway and Plant


A commonly heard phrase is “We can’t get density, can you raise the AC a little?”

Sounds benign, but presents a problemHow many times has that same question been asked before?

Might have developed “AC Creep” over the years.Exhaust all possibilities on the road before even thinking of raising AC%How much do extra roller passes or an extra roller cost per ton?

Varies, but likely not to same level as AC% increase.

Communication


COMPLACENCY• Norman Vincent Peale said “Opportunities are usually

disguised as hard work, so most people don't recognize them.”

COMMUNICATION• Various LOBs need to work together instead of being

independent

Silo mentality is a killer!• Mix designers must know the cost of materials during mix

design• “Who makes the final call on producing a high RAP mix?”• Designer can set the table with a mix design, but then

what?• Remember, we are all on the same team!

Mix Optimization Challenges and Obstacles


Performance Management ProcessConduct an initial review of your mixes for opportunitiesGet ALL parties to the table for input, discussion and buy in

Mix designers, production/operations (asphalt and internal aggregate), executive management

Develop action plan for mix optimization

Assign responsible partiesDevelop deadlines for task completionDevelop measures for determination of success.Conduct periodic review of mix optimization work conducted and potential opportunities

The Continuous Nature of Mix Optimization


You can never rest! Always remember….”Your competitor is working when you are not!”

Customers won’t necessarily buy your product because it has quality, but they certainly won’t buy it if it does not.Quality doesn’t start in the quality control department

Must be top driven throughout all levels of a company

“Success is neither magical nor mysterious. Success is the natural consequence of consistently applying the basic fundamentals.” (Jim Rohn)

Maintain Focus on Quality!


Shane Buchanan, Ph.D., P.E.Asphalt Performance ManagerOldcastle Materials [email protected] (cell)

Thank You!


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