2/5/2019 Mixture Design Part 1: Creating the Balance Shane Buchanan - - PDF document

2/5/2019 1

Mixture Design Part 1: Creating the Balance Shane Buchanan CRH Americas Materials Learning Objectives

1.

Understand the concept of Balanced Mixture Design.

2.

Review the most common performance tests (rutting and cracking) for BMD.

3.

Learn the current national state of practice for BMD.

4.

Understand how a BMD compares to a traditional volumetric design.

5.

Discuss how acceptance testing can be conducted with a BMD system.

6.

Learn how you can prepare for the future of asphalt mixture design.

7.

Discuss theory and reality pertaining to mix design.

What is Balanced Mix Design (BMD)?

2/5/2019 2

• “Asphalt mix design using performance

tests on appropriately conditioned specimens that address multiple modes of distress taking into consideration mix aging, traffic, climate and location within the pavement structure.”

• Use the right mix for the right job!

Balanced Mix Design Definition Selecting the Correct Mix

 Using the right mixture for the right job!  Don’t design a Ferrari, if a Pinto will do the job!  But if a Ferrari is needed, don’t

provide a Pinto! 1890

• Barber Asphalt Paving Company
• Asphalt cement 12 to 15% / Sand 70 to 83% / Pulverized carbonite of lime 5 to 15%

1905

• Clifford Richardson, New York Testing Company
• Surface sand mix: 100% passing No. 10, 15% passing No. 200, 9 to 14% asphalt
• Asphaltic concrete for lower layers, VMA terminology used, 2.2% more VMA than current day mixes or ~0.9% higher binder content

1920s

• Hubbard Field Method (Charles Hubbard and Frederick Field)
• Sand asphalt design
• 30 blow, 6” diameter with compression test (performance) asphaltic concrete design (Modified HF Method)

1927

• Francis Hveem (Caltrans)
• Surface area factors used to determine binder content; Hveem stabilometer and cohesionmeter used
• Air voids not used initially, mixes generally drier relative to others, fatigue cracking an issue

1943

• Bruce Marshall, Mississippi Highway Department
• Refined Hubbard Field method, standard compaction energy with drop hammer
• Initially, only used air voids and VFA, VMA added in 1962; stability and flow utilized

1993

• Superpave
• Level 1 (volumetric)
• Level 2 and 3 (performance based, but never implemented)

History of Mix Design

http://asphaltmagazine.com/history-of-asphalt-mix-design-in-north-america-part-2/

B I N D E R C O N T E N T L O W E R Stability Stability + Durability Stability + Durability

25 Years Without the Promised Performance Test!

2/5/2019 3

Why the need for BMD?

 Problems:

 Dry mixes exist in some areas.  Volumetrics alone can not adequately evaluate mix variables, such

as recycle, warm-mix additives, polymers, rejuvenators, and fibers.

 Solutions:

1.

Recognize performance issues related to dry mixes in some

• areas. (Note: Many performance issues are caused by factors
• utside the mix design.)

2.

Increase understanding of the factors which drive mix performance

3.

Design for performance and not just to “the spec”.

4.

Start thinking outside of long held “rules and constraints”

5.

Innovate!

Why the Need for a New Mix Design Approach?

 Each day, approximately 1.4

Million tons of HMA are produced in the U.S. (M-F production basis)

 Equivalent to ~2500 lane miles

@ 12’ wide and 1.5” thick

 Distance from New York to Las

Vegas

Importance of Quality Asphalt Mixtures

2/5/2019 4

Pavement Performance General Overview

 Achieving Balanced Mixture

Performance is Key to a Long Lasting Pavement

What Type Distress Is Occurring?

Source: Oldcastle Internal Survey

 Many agencies are lowering design gyrations (Ndesign)  Several states have selected one (1) Ndesign level for most all

mixtures

 Alabama (60), Ohio (65), Tennessee (65), Virginia, (65, 50)  Other states are still using excessively high Ndesign values (100+)  Need to have sufficient gyrations for develop / engage aggregate

blend structure.

 Too many gyrations result in breakdown and an unrealistically

high target density (field compaction problems).

 Caution: Lower gyrations do not necessarily equate to more

binder over the long term.

Agencies are Searching for Solutions: Ndesign

2/5/2019 5

What is the Main Key to Enhancing the Durability of Asphalt Mixtures?

 “Volume of Effective Binder (Vbe) is

the primary mixture design factor affecting both durability and fatigue cracking resistance.”

 Vbe = VMA – Air Voids

 “A number of state highway agencies

have decreased the design gyration levels in an attempt to increase effective binder contents. However, decreasing the design gyrations may not always produce mixtures with higher Vbe.”

 Superpave system is becoming

unrecognizable with specifications changing rapidly as agencies search for ways to improve durability

 Specifications have become

convoluted and confounded

 Existing specified items compete

against each other

 New requirements get added and

nothing gets removed

 Establishing true “cause and effect”

is impossible

Agencies Are Searching for Solutions: Spec Changes

Which of the following specification changes has your DOT implemented in the last 5 years? Source: Oldcastle Internal Survey

What are the most common performance tests (rutting and cracking) for BMD?

PERFORMANCE

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Main Pavement Distresses Observed in the Field

Source: NCAT

What Distress Does Your State Want to Address with Performance Testing?

Source: NCAT Survey

 Mixtures need to be evaluated in the lab during design to help ensure the

required field performance can be achieved.

Test Mixtures in the Lab to Help Ensure Field Performance

Lab Test (Hamburg Wheel Tracker) Lab Test Results Expected Field Performance

2/5/2019 7

Stability Testing (Rutting)

 Rutting can be evaluated with several available tests based on the user preference.

Rutting Tests

Hamburg Wheel Test (HWT) Asphalt Pavement Analyzer (APA) AMPT Flow Number / Dynamic Modulus Most commonly used tests. Hamburg gaining popularity due to moisture susceptibility analysis.

Durability Testing (Cracking)

2/5/2019 8

 Durability/cracking evaluation is substantially more

complicated than stability with aging being one main variable.

 No general consensus the best test(s) or the appropriate

failure threshold.

 MANY different tests are available with more being

developed.

 Main question is “What is the anticipated mode of

distress?”

Durability/Cracking Evaluation First Question for Durability Testing: What is the Anticipated Mode of Distress for Testing?

 Many test are available with each targeting a

specific specimen response (i.e., field distress)

 Various empirical and mechanistic tests are

available for use.

 Match apples to apples, not apples to oranges!

=

GOALS

• 1. MA

TCH THE TEST TO THE DISTRESS

• 2. SET APPROPRIA

TE FAILURE THRESHOLDS

Fatigue (Bottom Up or Top Down) Related Cracking Tests

Bending Beam Fatigue Texas Overlay Test SCB

• LTRC – Jc
• IFIT

Direct Tension Cyclic Fatigue, S-VECD Bottom Up Bottom Up Bottom Up / Top Down Bottom Up

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Thermal Cracking Tests

IDT Creep Compliance TSRST SCB at Low Temp Disk Shaped Compact Tension (DCT)

Reflection (Reflective) Cracking Tests

Disk Shaped Compact Tension (DCT) Texas Overlay Test SCB (IFIT)

IFIT Overview

Source: Brian Hill, Illinois Department of Transportation’s Implementation of I-FIT, NAPA Mid Year Meeting 2017

2/5/2019 10

IFIT Background Information

Americas Materials - Performance 2 8 IFIT

IDEAL CT Background Information

IDEAL CT

• Similar to IFIT
• Uncut!
• 62 mm height

specimen https://www.youtube.com/watch?v=OB 4pQDB2Yfs

Time View: 0:40 to 1:40

What is the current national state of practice for BMD?

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NCAT BMD Survey Results NCAT BMD Survey Results Illinois Balanced Mix Design

• Phased implementation
• Research started in 2012
• 26 Pilot projects 2016/2017
• All Interstate projects 2019
• Full implementation 2020

2/5/2019 12

Illinois BMD

http://publish.illinois.edu/bituminous/files/2016/12/4.-Imad-Al-Qadi.pdf

Louisiana Balanced Mix Design

• Louisiana DOT has

implemented BMD in the 2016 Standard Specifications for all DOT projects.

Hamburg Louisiana SCB

+

• Hamburg research began prior to 2000
• SCB research began in 2004

New Jersey Balanced Mix Design

• NJDOT High RAP Design

incorporates BMD

+

Asphalt Pavement Analyzer (APA) Texas Overlay Tester

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Texas DOT Balanced Mix Design

• TxDOT currently uses BMD for

selected specialty mixes.

• New SS 344 developed for

Superpave BMD.

+

Hamburg Texas Overlay Tester

From Robert Lee (TxDOT, Now CRH)

• SS 344 allows TxDOT Districts to use on a case by case

basis.

• Delta Tc (<6C) and Methylene Blue (<10) requirements
• Grade “dumps” reduced
• Simplified recycle material requirements

Texas DOT Balanced Mix Design Performance

From Robert Lee (TxDOT, Now CRH) Crack Initiation Parameter Crack Propagation Parameter

BMD Basic Example

• Texas DOT
• Volumetric design conducted
• Hamburg Wheel Tracking Test

(HWTT) AASHTO T 324

• Overlay Tester (OT) Tex-248-F
• Three asphalt binder contents are

used: optimum, optimum +0.5%, and

• ptimum -0.5%.
• The HWTT specimens are short-

term conditioned.

• The OT specimens are long-term

conditioned.

Within this acceptable range (5.3 to 5.8 percent), the mixture at the selected asphalt content must meet the Superpave volumetric criteria.

2/5/2019 14

Oklahoma DOT Balanced Mix Design Performance

Notes: Hamburg + IFIT @ 7% voids, Cantabro @ 4% Short term aging used (R30) (50C) Hamburg IFIT

+

ODOT Research

https://rip.trb.org/Results?txtKeywords=balanced+mix+design#/View/14974 63

“Anticipated Benefits: Development of draft specifications and draft supplemental specifications for a balanced mix design procedure for ODOT will move ODOT away from a voids based mix design procedure, allowing more innovative design concepts and producing longer lasting more durable and rut resistant pavements.”

Oklahoma DOT BMD Special Provision

• Trial pilot projects have been

awarded.

• APAC Central (OK) Pawhuska

plant.

• S4 70-28 Rec BMD (12%

RAP) “vs” standard (0% RAP) S4 70-28 insoluble

BMD Mix

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BMD Activities at the 2018 NCAT Test Track

• Balanced Mix Design is a key focus

area

• TXDOT (2 sections)
• Texas Bit Mix (Materials)
• OKDOT (2 sections)
• APAC Central (OK) Mix Design and

Materials

• Cargill (2 sections)

Performance Space Diagrams

• Performance testing

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

• Allows for effective

mix optimization!

• Meeting

requirements at lowest cost

Example Data for Illustration Purposes

Balanced Mix Design

Better Cracking Performance Better Rutting Performance

Good Performance

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Balanced Mix Design – The Future

• BMD / Performance Based Mix

Design is Coming!

• New Draft BMD AASHTO Standards

Current State DOT Research

• Various State DOTs have

current research activities focused on BMD related activities

State DOT Research Title California Simplified Performance Based Specifications for Long Life AC Pavements Idaho Development and Evaluation of Performance Measures to Augment Asphalt Mix Design in Idaho Indiana Performance Balanced Mix Designs for Indiana’s Asphalt Pavements Minnesota Balanced Design of Asphalt Mixtures Texas Develop Guidelines and Design Program for Hot-Mix Asphalts Containing RAP, RAS, and Other Additives through a Balanced Mix Design Process Wisconsin 1. Analysis and Feasibility of Asphalt Pavement Performance- Based Testing Specifications 2. Regressing Air Voids for Balanced HMA Mix Design Oklahoma Implement Balanced Asphalt Mix Design in Oklahoma

How does a BMD compare with a volumetric mix design?

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Balanced Mix Design Versus Conventional Mix Design

Step Marshall Balanced Mix Design

Select Asphalt Binder YES YES Select Virgin Aggregate YES YES Select Recycle Content YES YES Compact Specimens at a Range of Binder Contents YES YES Calculate Volumetric Properties YES YES Conduct Stability Performance Testing YES (Marshall Stability & Flow) YES (User Preference) Conduct "Durability" Performance Testing YES (Marshall Flow) YES (User Preference ) Evaluate Performance Tests Against Developed Criteria YES YES Select Optimum Binder Content YES YES Determine Volumetric Properties at Optimum Binder Content YES YES Evaluate Moisture Susceptibility at Optimum Binder Content YES YES Control Mixture During Production YES (Volumetrics) YES (Volumetrics and/or Performance Tests)

Volumetric Mix Design vs Balanced Mix Design (Example)

5.7% 6.2% VOLUMETRIC BALANCED Source: NCAT Balanced Mix Design Training Course Note: Example for Illustration Purposes.

Hamburg Threshold IFIT Threshold Hamburg Threshold IFIT Threshold IFIT Vol Actual Hamburg Vol Actual

Example: Engineering Mixes to Provide Performance

2/5/2019 18

Balanced Mix Design Experimental Work

Goals ▪ Determine if alternate mixes can provide equal to or better performance while considering the mix cost.

Mix Testing Overview

Utah Mix

• Control mix: 12.5 mm surface mix with

25% RAP

• Alternate mixes: 35% and 45% RAP w/

POET JIVE rejuvenator

• Performance Testing
• 1. Illinois Flexibility Index (IFIT)
• 2. IDEAL CT
• 3. Hamburg

IFIT IDEAL CT HAMBURG Aging: STA @ 275F for 4 hours

Utah Mix Testing – IFIT Results

Americas Materials - Performance 5 4

3.9 7.2 14.6 4.4 8.3 17.7 3.7 5.2 10.1 0.0 2.0 4.0 6.0 8.0 10.0 12.0 14.0 16.0 18.0 20.0

• OPT. - 0.5

OPT

• OPT. + 0.5
• OPT. - 0.5

OPT

• OPT. + 0.5
• OPT. - 0.5

OPT

• OPT. + 0.5

8 8 25 35 45 FLEXIBILITY INDEX IFIT BINDER REJUVENATOR RAP

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Utah Mix Testing – IDEAL CT Results

Americas Materials - Performance 5 5

51.5 81.5 160.3 50.2 86.2 205.3 35.0 69.9 142.8 0.0 50.0 100.0 150.0 200.0 250.0

• OPT. - 0.5

OPT

• OPT. + 0.5
• OPT. - 0.5

OPT

• OPT. + 0.5
• OPT. - 0.5

OPT

• OPT. + 0.5

8 8 25 35 45 IDEAL CT INDEX

IDEAL CT

BINDER REJUVENATOR RAP

Utah Mix Testing – Hamburg Results

Americas Materials - Performance 5 6

2.4 2.6 4.2 3.0 4.0 4.7 2.4 3.2 3.8 0.0 2.0 4.0 6.0 8.0 10.0 12.0 14.0 OPT - 0.5 OPT OPT + 0.5 OPT - 0.5 OPT OPT + 0.5 OPT - 0.5 OPT OPT + 0.5 0% 8% 8% 25 35 45 RUT DEPTH (MM) @ 20K PASSES HAMBURG BINDER REJUVENATOR RAP

Utah Mix Testing – IDEAL CT vs IFIT

Americas Materials - Performance 5 7

y = 11.399x - 1.6644 R² = 0.9916 50 100 150 200 250 2 4 6 8 10 12 14 16 18 20 IDEAL CT IFIT IDEAL CT vs IFIT

Takeaway: Can use IDEAL CT during production as a quicker control tool.

2/5/2019 20

Utah Mix Testing – Performance Space Diagram (Hamburg vs IFIT)

$(2.67) $2.66 $(4.47) $(1.81) $0.86 $(6.91) $(4.24) $(1.58) $(8) $(6) $(4) $(2) $- $2 $4

MATERIALS COST

BASELINE MIX

Utah Mix Testing – More IFIT Results

Americas Materials - Performance 5 9

BINDER REJUVENATOR RAP AGING

Specimen Aging

Short Term Oven Aging (STOA)

• 4 hr. @ 135C (275F) as recommended in AASHTO R30 for mixture

performance testing. Long Term Oven Aging or Critical Aging (CA)

• Used NCATs cumulative degree days (CDD) aging protocol.
• 8 hr. @ 135C (275F) in addition to the STOA

2/5/2019 21

Critical Aging Protocol and CDD

• The top down cracking critical aging protocols of

8 hours at 135C were proposed based on their correspondence with 70,000 CDD.

• Aging protocol remains constant regardless of

location, but it would take more years for a project in a colder climate to reach 70,000 CDD than a project in a warmer climate.

• For example, PA needs 5.7 years but AL only

requires 4.3 years.

CDD

5.5 Years to 70,000 CDD for SLC

What about acceptance testing with a BMD approach?

2/5/2019 22

BMD Field Acceptance - Approaches

Graphic Developed by Kevin Hall (FHWA BMD Task Force), 9/14/2017

 Any designed mixture must be

produced and controlled to help ensure acceptable field performance.

 Three general field acceptance

approaches.

1.

Volumetric

2.

Volumetrics + Performance

3.

Performance

What’s the future of BMD? So…I’m a Agency Engineer, What to Do to Prepare?

1. Remember, it’s still aggregate, asphalt, and air! 2. Be aware of what’s happening 3. Participate in conferences/meetings 4. Evaluate your readiness (e.g., capabilities / needs). Do you need to more people, training, equipment? 5. Act to increase readiness 6. Establish baseline (test your mixes to see where you are at) 7. Establish appropriate protocols for design and acceptance 8. Embrace the opportunity! 9. Be the leader! “By failing to prepare, you are preparing to fail.”

• Ben Franklin

2/5/2019 23

So…I’m a Contractor, What to Do to Prepare?

1. Remember, it’s still aggregate, asphalt, and air! 2. Be aware of what’s happening 3. Participate in conferences/meetings 4. Understand the impact of BMD on asphalt binder demand, recycle potential / availability 5. Evaluate your readiness (e.g., capabilities / needs). Do you need to more people, training, equipment? 6. Act to increase readiness 7. Establish baseline (test your mixes to see where you are at) 8. Optimize mixes (performance + economics) 9. Embrace the opportunity!

• 10. Be the leader!

“By failing to prepare, you are preparing to fail.”

• Ben Franklin

The Path Forward for Balanced Mix Design

 Long term effort with ups/downs, but we

must start now.

 Utilize available, proven approaches to find

effective, implementable solutions.

 Completion of 20-07 Task 406 and the

developed AASHTO recommended practice will aid use / implementation.

Be Aware of the Total Picture!

Materials Production Construction Equipment Personnel Economics Time

2/5/2019 24

• Avoid measuring with a micrometer, marking with a piece of chalk and cutting with an ax.
• Must consider the production/construction capability as part of the design and specification

process.

• Avoid consistently unachievable targets.
• Applied common sense MUST be used.

Theory and Reality

• Keep it Simple, Stupid!
• Design principle noted by the U.S. Navy in 1960
• The principle is best exemplified by the story of Kelly

Johnson, lead engineer at the Lockheed Skunk Works (creators of the Lockheed U-2 and SR-71 Blackbird spy planes)

• Used the phrase when handing a team of design

engineers a handful of tools, with the challenge that the jet aircraft they were designing must be repairable by an average mechanic in the field under combat conditions with only these tools.

KISS Principle

 Key Points to Keep in Mind

1.

“Use What Works”

2.

“Eliminate What Doesn’t”

3.

“Be as Simple as Possible, Be Practical, and Be Correct”

Final Thoughts

http://twentytwowords.com

2/5/2019 25

Questions

http://www.pennyauctionwatch.com/

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

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