Rubberized Asphalt – The Arizona Experience Julie.pdf · ADOT Rubber Mixes AR-ACFC Final wearing surface (friction course) ARAC Structural Lift

Asphalt Rubber: The Arizona Experience

Julie Kliewer, Ph.D., PEArizona Department of

Transportation

What is Asphalt Rubber?

A mixture of Aggregate Asphalt Rubber Binder (crumb rubber +

asphalt cement)

Ground Tire Rubber

ADOT Rubber Mixes

AR-ACFC Final wearing surface (friction course)

ARAC Structural Lift

History: I-19 Project (1988)

10.0 % asphalt rubber by weight of mix Placed on plain jointed concrete

pavement First reflection cracks noted in 1996 Sections no longer in service because of

I-10/I-19 interchange project not because of poor performance

Experimented with recycling in this section

History: ARAC

1990 placed on I-40 near Flagstaff 2” thick Structural Overlay Gap graded mix Placed on severely cracked and failed

concrete pavement Least reflection cracking of any

application

Usage

050

100150200250300350400450

1985 1990 1995 2000 2005

Thou

sand

s

Tons

Mix

ARACAR-ACFC

ADOT ARAC and AR-ACFC Usage

Year Tons of mix Est. Tires Recycled

2004 872,155 2,512,500

2003 480,260 1,921,040

2002 450,570 1,802,280

2001 450,790 1,803,160

2000 481,566 1,926,264

1999 687,914 2,100,000

About 1000 Tires Per Lane Mile

What does Asphalt Rubber do for us? Nature of asphalt rubber binder allows the

use of approximately 2% more binder than with asphalt cement

Elastic properties slow reflective cracking Asphalt rubber binder does not seem to age

as rapidly as asphalt cement It lasts! Reduces noise It is not without its cost$$

Asphalt Cements in CRA

Type 1 Hot Climate PG 64-16 (Phoenix) Type 2 Moderate Climate PG 58-22

(Prescott, Flagstaff) Type 3 Cold Climate PG 52-28 (Alpine,

highest elevations)

CRA Properties Influenced by

Asphalt Cement

Amount of crumb rubber

Crumb rubber gradation

Reaction temperature and time

Viscosity

Monitors fluid consistency of binder to:

Ensure pumpability

Identify binder changes which might affect mix placement and compaction

Can be done in field

Resilience Appears to be a reliable measure of the

elastic properties of the asphalt rubber binder.

Expressed as a percentage of rebound for the binder.

Resilience is one of the most important properties of AR binders and is considered a primary indicator of performance.

Design of Asphalt Rubber Mixtures

AR-ACFCARAC

AR-ACFC

A: Asphalt R: Rubber - A: Asphaltic C: Concrete F: Friction C: Course

AR-ACFC

Open graded (not free draining) Typically around 9.5% asphalt rubber (by wt

of total mix) (range 8.9% to 10.0%) Used as final wearing surface, not structural On asphalt pavements, typically ½ inch thick On concrete pavements, typically 1 inch thick

AR-ACFC Mix Design

Aggregate basically 95% 3/8” chips and 5% fines

Get as much asphalt rubber binder in the mix as possible without draindown

AR-ACFC Mix Design: Determining Binder Content

Starting binder content estimated by equation

Starting point may be adjusted based on history

Check draindown Adjust binder content as needed

AR-ACFC: Design

1. Place Mix in a beaker

2. Place beaker in oven for 1 hour

3. Empty beaker

4. Determine % mass loss

How much rubber in AR-ACFC

20% rubber by weight of asphalt cement

Approximately 9.5% asphalt rubber binder in mix

Works out to about 1.75% rubber in the mix

ARAC

A: Asphalt R: Rubber A: Asphaltic C: Concrete

ARAC

Gap graded (to allow space for rubber particles)

Typical binder contents 6.5% to 8.0%

ARAC Design

Design for 4.5 to 6.5% air voids

Minimum VMA specified

Have to watch for building of VMA by binder

Costs (a little outdated)

ACFC $1.60/sy AR-ACFC $2.20/sy

AC(3/4) $2.25/sy/in ARAC $3.25/sy/in

Asphalt Rubber $300/ton Asphalt Cement $200/ton

Asphalt Rubber

How is it made?

Asphalt Rubber Binder

Minimum 20% crumb rubber by weight of asphalt cement

Crumb rubber added to 350 – 400°F asphalt cement

Crumb rubber and asphalt cement mixed

Asphalt rubber reacted for at least one hour at 325 – 375° with agitation

An aerial view of a portable Asphalt-RubberPlant setup at a Hotplant.

BLENDER

Hotplant

AR BLEND TANK

VIRGIN AC TANKRUBBER STAGING AREA

High Shear Mixer

Mix Placement

Quiet Pavments Program

Quiet Pavement Pilot Program Arizona QPPP consists of

Initial research to demonstrate performance of existing and proposed pavement

Overlaying new and existing PCC with ARFC

4 dB credit for lower tire/pavement noise On-going testing to track pavement

performance

Noise Levels By Surface Type (CPX)

105 Random Transverse (Wisconsin)

102 Uniform Transverse (ADOT-3/4”)

99 Longitudinal (ADOT-3/4”)

99 Whisper Grind

94 ARFC

Asphalt Rubber Performance

0

10

20

30

40

50

60

70

80

90

100

0 2 4 6 8 10 12

Age (YR)

Rid

e (In

./Mile

)

PCCPPCCP_ARFC

Smoothness

25

30

35

40

45

50

55

60

65

70

0 2 4 6 8 10 12

Age

Mu

PCCPPCCP_ARFCDesired Level

Friction Levels

Rut Depth vs. Age

0

0.05

0.1

0.15

0.2

0.25

0.3

0 1 2 3 4 5 6 7 8 9 10

Year

Rut

Dep

th ,

inch

es

Overlays / Inlays

AR-ACFC

Rutting

Maintenance Cost $/lane -Mile

0

200

400

600

800

1000

1200

1400

1600

0 2 4 6 8 10 12

Year

Mai

nt.

Cos

t

Overlays / Inlays Neat asphalt only

Asphalt Rubber projects

Maintenance Costs

Percent Cracking vs Age

0123456789

10111213

0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16

Years

% C

rack

ing

Overlays / InlaysNeat asphalt only

Asphalt Rubberprojects

Cracking

Smoothness vs Age for AC pavements

01020304050607080

0 1 2 3 4 5 6 7 8 9 10 11

Year

Inch

. / M

ile

ACFC

AR-ACFC

Smoothness (AR-ACFC v. ACFC)

Friction Vs. Age

30

35

40

45

50

55

60

65

70

0 1 2 3 4 5 6 7 8 9 10 11

Year

Mu

Met

er n

umbe

r

ACFC

AR-ACFC

Friction LevelsAR-ACFC v. ACFC

I-17 SB ARFC placed in 1994, elev. 6800‘

I-17 SB MP 312 – 337

I-17 SB MP 312 - 337

0

50

100

150

200

250

1992

1993

1994

1995

1996

1997

1998

1999

2000

2001

2002

Year

Cra

ckin

g (%

)R

ough

ness

(in/

mi)

RoughnessCracking

I-19 AR-ACFCplaced in 1989, elev. 2700’

I-19, MP 59, Roughness/Cracking vs Age

020406080

100120140160

1987

1988

1989

1990

1991

1992

1993

1994

1995

1996

1997

1998

1999

2000

2001

Year

Cra

ck (

%)

Ro

ug

hn

ess

(in

/mi)

Series1

Series2

Cracking

Roughness

I-19 Project built in 1989

AR-ACFC Recycling Research

Hot-in-place proof of concept I-19 Project

Hot-in-place Hot plant (20% and 30% RAP) using

terminal blend Constructed in 2006, performing well

Its Perfect, isn’t it?

When things go wrong….

I-17

Problem 1

I-17

The new Problem

Jack Rabbit

SR 260

The Summer Problem