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3/12/2019
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Balanced Mix Designs -Improving Mix Durability
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Discussion Items
Americas Materials - Performance2
• Understand the concept of Balanced Mixture Design.
• Review the most common performance tests (rutting and cracking) for BMD.
• Learn the current national state of practice for BMD.
• Learn how you can prepare for the future of asphalt mixture design.
• Discuss theory and reality pertaining to mix design.
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Balanced Mix Design
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Mix design based on balancing mix rutting and cracking performance instead of conventional recipe, restrictive specifications.
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Selecting the Correct Mix
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• Understand the concept of Balanced Mixture Design.
• Don’t design a Ferrari, if a Pinto will do the job!
• But if a Ferrari is needed, don’t provide a Pinto!
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Did You Know…..
Americas Materials - Performance5
• 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
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Main Pavement Distresses Observed in the Field
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What Distress Does Your State Want to Address with Performance Testing?
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Source: NCAT Survey
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What are the Most Common Performance Tests (Rutting and Cracking) for BMD?
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Rutting Tests
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Rutting Tests
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• Rutting can be evaluated with several available tests based on the user preference.
Hamburg Wheel Test (HWT) Asphalt Pavement Analyzer (APA)
Most commonly used tests. Hamburg gaining popularity due to moisture susceptibility analysis.
AMPT Flow Number / Dynamic Modulus
IDT - HT
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Durability Testing (Cracking)
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Durability/Cracking Evaluation
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• 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?”
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First Question for Durability Testing: What is the Anticipated Mode of Distress for Testing?
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• 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!
GOALS1. MATCH THE TEST TO THE DISTRESS2. SET APPROPRIATE FAILURE THRESHOLDS
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Fatigue (Bottom Up or Top Down) Related Cracking Tests
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IDEAL CT
Bottom Up / Top Down
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Thermal Cracking Tests
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IDT Creep Compliance
TSRST SCB at Low Temp Disk Shaped Compact Tension (DCT)
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Reflection (Reflective) Cracking Tests
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Disk Shaped Compact Tension (DCT)
Texas Overlay Test SCB (IFIT)
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IFIT Background Information
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IFIT
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IDEAL CT Background Information
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- Similar to IFIT
- Uncut!
- 62 mm height specimen
https://www.youtube.com/watch?v=OB4pQDB2Yfs
Time View: 0:40 to 1:40
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Balanced Mix Design
Americas Materials - Performance19
Good Performance
Better Cracking Performance Bet
ter
Rut
ting
Per
form
ance
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Case Study
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• CRH is Funding Balanced Mix Design Proof of Concept Testing
• Staker Parson (Utah) Mix Evaluated
• Testing Conducted at National Center for Asphalt Technology
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Staker Parson Mix Testing Overview
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Staker Parson (Keigley Plant)
▪ Control mix: 12.5 mm surface mix with 25% RAP
▪ Alternate mixes: 35% and 45% RAP w/ rejuvenator
▪ Performance Testing
1. Illinois Flexibility Index (IFIT)
2. IDEAL CT
3. Hamburg
IFIT IDEAL CT
HAMBURG
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Specimen Aging
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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
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Critical Aging Protocol and CDD
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• 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.
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CDD
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5.5 Years to 70,000 CDD for SLC
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Staker Parson Mix Testing –Hamburg Results
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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 DEP
TH (MM) @ 20K
PASSES
HAMBURG
BINDER
REJUVENATOR
RAP
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Staker Parson Mix Testing – IFIT Results
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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
0 8 8
25 35 45
FLEX
IBILITY INDEX
IFIT
BINDER
REJUVENATOR
RAP
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Staker Parson Mix Testing
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BINDER
REJUVENATOR
RAP
AGING
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Staker Parson Mix Testing –IDEAL CT Results
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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
0 8 8
25 35 45
IDEA
L CT INDEX
IDEAL CT
BINDER
REJUVENATOR
RAP
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Staker Parson 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
$4MATERIALS COST
BASELINEMIX
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Staker Parson Mix Testing –IDEAL CT vs IFIT
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y = 11.399x ‐ 1.6644R² = 0.9916
0
50
100
150
200
250
0 2 4 6 8 10 12 14 16 18 20
IDEA
L CT
IFIT
IDEAL CT vs IFIT
Takeaway: Can use IDEAL CT during production as a quicker control tool.
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NCAT BMD Survey Results
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NCAT BMD Survey Results – State Interest in BMD
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Illinois Balanced Mix Design
• Phased implementation
▪ 26 Pilot projects 2016/2017
▪ All Interstate projects 2019
▪ Full implementation 2020
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Louisiana Balanced Mix Design
• Louisiana DOT implemented BMD in the 2016 Standard Specifications for all DOT projects.
Hamburg Louisiana SCB
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• Hamburg research began prior to 2000• SCB research began in 2004
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New Jersey Balanced Mix Design
• NJDOT High RAP Design incorporates BMD
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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.
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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
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Texas DOT Balanced Mix Design Performance
From Robert Lee (TxDOT, Now CRH)
Crack Initiation ParameterCrack Propagation Parameter
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Oklahoma DOT Balanced Mix Design Performance
Notes:Hamburg + IFIT @ 7% voids, Cantabro @ 4%Short term aging used (R30)
(50C)
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Hamburg IFIT
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BMD Activities at the 2018 NCAT Test Track
• Balanced Mix Design is a key focus area
• TXDOT
• OKDOT
• Cargill (w/ VA design)
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Current / Completed State DOT Research
• Various State DOTs have research activities focused on BMD
State DOT Research Title
California Simplified Performance Based Specifications for Long Life AC Pavements (Funding unknown)
Idaho Development and Evaluation of Performance Measures to Augment Asphalt Mix Design in Idaho (170K)
Indiana Performance Balanced Mix Designs for Indiana’s Asphalt Pavements (243K)
Minnesota Balanced Design of Asphalt Mixtures (140K)
Texas Develop Guidelines and Design Program for Hot-Mix Asphalts Containing RAP, RAS, and Other Additives through a Balanced Mix Design Process (524K)
Wisconsin 1. Analysis and Feasibility of Asphalt Pavement Performance-Based Testing Specifications (Funding Unknown, completed)
2. Regressing Air Voids for Balanced HMA Mix Design (150K)
Oklahoma Implement Balanced Asphalt Mix Design in Oklahoma (111K)
Nebraska Feasibility and Implementation of Balanced Mix Design in Nebraska (120K)
Virginia Performance Mixture Design for Asphalt Mixtures: Phase I, Roadmap and Specification Development (456K)
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Balanced Mix Design – The Future
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• BMD / Performance Based Mix Design is Coming!
• New Draft BMD AASHTO Standards
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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 to learn more
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
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So…I’m a Contractor / Producer, 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 to learn more
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!
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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.
• Must consider testing during production.
• IDEAL CT offers promise in this regard for fast, reliable rutting and cracking performance prediction.
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Materials
Production
Construction
EquipmentPersonnel
Economics
Time
Be Aware of the Total Picture!
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Theory and Reality
• Avoid measuring with a micrometer, marking with a piece of chalk and cutting with an ax.
• Must consider the “total picture” and not just a part.
• Applied Common Sense MUST be used.
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Final Thoughts
• Key Points to Keep in Mind
• “Use What Works”
• “Eliminate What Doesn’t”
• “Be as Simple as Possible, Be Practical, and Be Correct”
http://twentytwowords.com
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Thank You / Questions
http://www.pennyauctionwatch.com/
Shane BuchananAsphalt Performance Manager CRH Americas [email protected]
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