What is Asphalt Rubber?
A mixture of Aggregate Asphalt Rubber Binder (crumb rubber +
asphalt cement)
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
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
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.
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 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 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
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
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
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 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, 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