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