Chip SealingThe Nuts and Bolts

Thomas J. WoodResearch Project Supervisor

MN/DOT

Why do we do Pavement Preservation?

The Answer is?

• To keep new pavements new longer!• Is Pavement Preservation Cost Effective

– Yes• But depends on properly constructed projects.

• How do we know it is Cost Effective?– Anecdotal evidence – Pavement Management Data

• Mn/DOT experiences

Seal CoatedSR = -0.0008x2 - 0.0307x + 4.0111

R2 = 0.7934

No Maint.SR = -0.0041x2 - 0.0103x + 3.9607

R2 = 0.8967

0.0

0.5

1.0

1.5

2.0

2.5

3.0

3.5

4.0

0 2 4 6 8 10 12 14 16 18 20

Years since BAB Construction

Ave

rage

SR

No Maintenance Seal Coated Poly. (Seal Coated) Poly. (No Maintenance)

Ride:

0.00.51.01.52.02.53.03.54.0

0 5 10 15 20

Pavement Age, years

Rid

e Q

ualit

y In

dex

No Preservation With Preservation

Chip Sealing

What Is a Seal Coat

• Bituminous surface treatment– Heavy asphalt binder membrane– Followed by aggregate chip

Topics!• Seal Coat Handbook• Chip Seal Design• Aggregate requirements• Binders• Construction Details• Fog Sealing• Tips

Originally Published in 1997

• Two main parts– Chapters 1- 4

• Materials and Design

– Chapters 5 – 8• In the Field

• Has had a pay back ratio of 77 to 1

Revised in 2006

• What’s has been updated?• 3 new chapters

– Fog Sealing– Chip Sealing for Recreational Trails– Frequently Asked Question About Chip Sealing

• Updated technical information.

Seal Coat DesignWhat does this design method do

1. Gives amount of stone to cover 1 yd² a single stone thick

2. Gives starting binder application rate• Starting rate should yield 60 to 70%

embedment

• Design for 3/8 inch chip– Without design av. 30 lbs./Yd.²– Without design av. Binder 0.30 gal./Yd.²– With design av. 17 lbs./Yd.²– With design av. Binder 0.36 gal./Yd.²

Seal Coat Design Summary

Metro FA-3 chip seal 05

0.28

0.29

0.30

0.31

0.32

0.33

0.34

0.35

0.36

0.37

0.38

0.39

0.40

0.41

0.42

0.43

0.44

0.45

0.46

Under 100100 to 500500 to 1,0001,000 to 2,000Over 2,000

TRAFFIC VOLUME (ADT)

BIN

DER

APP

LIC

ATI

ON

RA

TE (g

al/y

d2 )

Badly pocked, porous, and oxidized

Slightly pocked, porous, and oxidized

Slightly porous, and oxidized

Seal Coat Design Summary

Designing and properly constructing your Seal Coats you can do more miles with less

money with better results.

Aggregate Requirements

– Must be clean • Clay free aggregate• Less then 1% passing #200

– Durable • LAR loss % max. 37%

– Flakiness index• Max. 25%

– Crushing• 80 % one face crushed.

Flaky Vs. Cubical Aggregates

Flat Chips

CHIP LOSS CHIP LOSS

There is not enough binder in the non-traffic areas toprevent traffic and snow plows from dislodging the chips.

If the seal coat is designed for chips in thewheelpaths:

Flat Chips

There is too much binder in the wheelpaths after the flatchips lay on their flattest side.

BLEEDING

If the seal coat is designed for chips in thenon- traffic areas:

Flaky vs. Cubical Aggregate

Flakiness Testing Methods

CurrentMethod

NewMethod

Dense Graded Vs. Single Size!

0

10

20

30

40

50

60

70

80

90

100

0 0.1 0.2 0.3 0.4 0.5 0.6

SIEVE SIZE, inches

PER

CEN

T PA

SSIN

G

dense gradedsingle sized

Dense Graded vs. Single Sized

Advantages of Single Sized Agg.• Single sized aggregate

– More uniform height – Weighs less per cubic foot

• 47% passing the #4 95.7 lbs/ft3

• 8% passing the #4 84.5 lbs/ft3

– More room for binder• Increased Voids

Advantages of Single Sized Agg.

– MM FA-2.5 $22.80 ton dense graded• 18.5 pounds / yard needed

– $0.211 / yard

• Single size– 14.5 pounds / yard needed– $0.165 / yard

– You can pay up to $6.30 a ton more for single sized chip and the total cost per square yard will be the same as dense grade chip.

Binders• CRS-2p (cationic rapid set polymer mod.).

– Develops strength in hrs instead of days.– Can be swept same day.– Requires use of clean aggregates.– Must place aggregate within 1 min. Of binder placement.– Eliminates bleeding.

• Higher softening point.– CRS-2 average softening point 108° F– CRS-2p average softening point 128° F

Construction Details

Distributors

YESSame Angle

NODifferent Angles

Fans are the same widthFans are the same width Fans are different widthsFans are different widths

Poor Spray Pattern!

Proper Spray Pattern!

Bar Height

PluggedNozzle

Chip Spreaders

ASTM D5624-95

Other Issues!

Fog Sealing

TopicsTopics

•• What is a Fog Seal?What is a Fog Seal?•• What’s new in Fog Sealing?What’s new in Fog Sealing?•• What are the Benefits of Fog Sealing of a What are the Benefits of Fog Sealing of a

chip seal?chip seal?–– Construction Issues.Construction Issues.

•• Fog Sealing for Recreation TrailsFog Sealing for Recreation Trails

What is a Fog Seal?What is a Fog Seal?•• It is a light uniform application of asphalt It is a light uniform application of asphalt

emulsion.emulsion.•• Normally CSSNormally CSS--1h or SS1h or SS--1h1h•• Cationic or Anionic Cationic or Anionic •• Strongly recommend it be diluted.Strongly recommend it be diluted.

–– Lower viscosity Lower viscosity –– Better penetration Better penetration

•• Application rate between .06 to .20 gallon per Application rate between .06 to .20 gallon per square yard diluted. square yard diluted.

Why Fog Seal Chip Seal?Why Fog Seal Chip Seal?

How does Fog Sealing help limit How does Fog Sealing help limit snowplow damage?snowplow damage?

•• Increased embedment.Increased embedment.–– Additional residual asphalt .Additional residual asphalt .–– Accelerates curing of pavement because of dark Accelerates curing of pavement because of dark

color.color.

•• Combination of binders.Combination of binders.–– Combination of soft elastomeric asphalt Combination of soft elastomeric asphalt

underneath and harder asphalt over top?underneath and harder asphalt over top?

Other benefits of Fog Sealing Other benefits of Fog Sealing Chip SealsChip Seals

•• Locks down marginally embedded chips.Locks down marginally embedded chips.•• Make pavement marking more visibly. Make pavement marking more visibly.

–– Reduces amount of paint needed.Reduces amount of paint needed.

•• Customer perceives surface treatment as a Customer perceives surface treatment as a new HMA overlay not a chip seal. new HMA overlay not a chip seal.

Construction IssuesConstruction Issues•• No rain forecasted for next 3 hoursNo rain forecasted for next 3 hours•• Environmental conditions dictates speed of cure.Environmental conditions dictates speed of cure.•• Proper nozzle size for uniform application.Proper nozzle size for uniform application.•• Properly functioning equipment and qualified Properly functioning equipment and qualified

operator.operator.•• Overlap the centerline at least 1 foot.Overlap the centerline at least 1 foot.•• Light coat of sand in intersections/high volume Light coat of sand in intersections/high volume

areas.areas.

What the Traveling Public See!

3 Years after Fog Seal

What new in Fog Sealing?

• Polymer modified asphalt emulsions– CRS-2pd

• Withstand UV aging better then non-modified asphalts

• Cures faster.• Less tracking

Tips for Successful Seal Coat• Make sure pavement is clean• Use high quality materials• Proper application rate for binder• Proper application rate for aggregate

– Excess aggregate only causes failure– Extra cost and waste

Tips for Successful Seal Coat

• Final sweeping of roadway as soon as possible.– No later then next morning.

• Quality does not cost. It pays!• Remember that details count.

Tips for Successful Seal Coat

• Minimum distance between distributor & chip spreader– Aggregate must be placed before emulsion

starts to break• Minimum of three rollers; Speed under 5 mph

– Compaction must be completed before emulsion is broken

Questions?

Thank You!