BALANCED MIX DESIGN
CAPTG WORKSHOP
2018 SWIFT CONFERENCE
Vince Aurilio, P.Eng.
Executive Director
Ontario Asphalt Pavement Council
Oldcastle
Distress Type Percentage of Respondents
Longitudinal Cracking 53
Reflective Cracking 44
Ravelling 30
Thermal Cracking 21
Fatigue Cracking 16
Slippage 16
Top Down Cracking 12
Stripping 7
Rutting 7
Oldcastle Survey – Key Distress Types Identified
Specification Adjustments
Specification Changes Made Percentage of Respondents
Grade Bumping 44
Lowered Ndesign 42
Other 37
Lowered Design Air Voids 30
Performance Testing (Rutting) 30
Lowered Reclaimed Asphalt Pavement(RAP) %
26
Performance Testing (Cracking) 26
Increased Design Voids in the MineralAggregate (VMA)
23
Mixture Design Changes
Mixture Changes
Percentage of Respondents
Increased Production Voids in the MineralAggregate (VMA)
23
Set Minimum Binder (Pb) Content 16
Lowered Recycled Asphalt Shingle (RAS)Content
14
Increased Quality Control and Assurance(QC/QA) Testing
14
Eliminated RAS 12
Increased Field Density 12
None of the Above 12
Set Minimum Effective Binder 7
WHAT HAS CHANGED?
1901 – 2000 Age of Uncomplicated
Almost all unmodified asphalt
Recycling in 1970s – 90s: Low amounts of RAP
Almost all dense-graded mixes
Marshall and Hveem become displaced
Volumetric design worked OK
Recycled as Asphalt Roads
HOW HAVE ASPHALT MATERIALS
CHANGED?
2000 – 2016
PG System in full swing
Refineries change – asphalt gets expensive
Warm mix
PPA to make high PG
REOB to make low PG
Polymers
More RAP and RAS
Smaller NMAS
SMAs
REFINERY CHANGES
Process Changes
Cokers
More terminal blenders
EXAMPLES
Texas
West Texas: Faster Aging
Venezuelan: Slower Aging
California
Coastal: Faster Aging
Valley: Slower Aging
Fluxes and Additives to Produce Specific Grades
REOB
PPA
4 months old
REOB AND PPA
Recycled Engine Oil Bottoms (Steve Escobar)
Most common additive in the US
High flash point, high viscosity index, low wt. loss, low viscosity, etc.
Also paraffinic
Polyphosphoric Acid (TRB Circular E-C160)
Commonly used additive
High viscosity, no free H2O, does not oxidize asphalt or lower m-value
May react with anti-strip
Both are dependent upon asphalt chemistry!
UNDERSTANDING THE PROBLEM
Accelerated embrittlement of asphalt leading to premature cracking.
1. Oxidative Aging: oxygen interacts with asphalt molecules which makes it less pliable. Like skin aging. Irreversible.
2. Physical Hardening: during extended periods of cold temperature, wax crystals get “squeezed” out of asphalt making it even more brittle at cold temperatures. Happens in some polymers. Reversible.
OXIDATIVE AGING AND PHYSICAL HARDENING
Aging
RAP/RAS vs. virgin
Asphalt absorption by aggregates
Binder chemistry
Location in pavement
Air Voids
Physical Hardening
Binder chemistry
RAP AND RAS
Resource Conservation
Energy Conservation
Price Stabilization
Needs Engineering for High %
Rejuvenators vs. Virgin
RAS – Low Levels Only
Air Blown
Too Hard
SUSTAINABILITY
Benefit of RAP/RAS
Economics
Saving aggregates
Saving asphalt binder
Reducing rutting
Environment
Reducing demands of non-renewable resources
Reducing landfill space demands
RAP/RAS must be used!
GREENHOUSE GASES
Pavement construction very
low compared to vehicle
operations
82 MT for pavements out of
1600 MT for all transportation
Using RAP/RAS reduces CO2e
about the same amount as
removing 270,000 vehicles
COST SAVINGS
Reference Material Cost Savings
Zhou et al. (2006) 5% RAS 2 – 5%
Brock (2008) 20% RAP
50% RAP
>16%
>40%
NCAT (Willis et al.,
2012)*
25% RAP
50% RAP
14 – 20%
29 – 35%
* Used different amounts and stiffness of virgin binders used in mixtures.
RAP/RAS AND PGRAP/RAS binder too stiff?
OTHER CAUSES OF CRACKING
Chemical/Physical
properties of binder
Assuming adequate
pavement thickness:
Lack of bonding between
pavement layers
Asphalt mixture characteristics
Earthquakes!
LACK OF BONDING BETWEEN LAYERS
DENSE GRADATION
No Room
for
Asphalt
COARSE GRADATION
Permeable
and Weak
GOOD GRADATION!
Room
for
Asphalt
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.”
BMD – Definition…
BALANCED MIX DESIGN
Cracking Rutting
Mix Design
RUTTING TESTS
DURABILITY CRACKING TESTS
DURABILITY CRACKING TESTS
FATIGUE CRACKING TESTS
THERMAL CRACKING TESTS
REFLECTIVE CRACKING TESTS
9-57 PROJECT OBJECTIVES Identify cracking tests for Thermal, Reflection, Top-Down fatigue, Bottom-Up fatigue
Literature review
State survey
Workshop
Develop experimental design for field validation
Experimental design
Plans for sampling, storing, shipping and testing materials
Estimated schedule and budget
Develop plans for laboratory evaluation
Precision and Bias
Ruggedness
November 2015NCHRP 9-57
BALANCED MIX DESIGN
Hamburg test for rutting/moisture damage
Overlay test for cracking
OT requirement determined by Overlay program
Max. density-98% for controlling potential bleeding
HOW DO WE DEAL WITH THIS?
November 2015
Balanced Mix
Design
Opt. AC
Set
Volumetric
QC Volumetrics
QA VolumetricsQA Performance
Testing
Set
Tolerances
FUTURE WORK
Establish Lab Aging
Procedure
Validate Cracking
Criteria
Develop QC/QA
Processes
Improve
Precision/Repeatability