durability & safety advantages of asphalt rubber pavements
TRANSCRIPT
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Durability & Safety Advantages
of Asphalt Rubber Pavements
Dale A. Rand, P.E. – TxDOT
Director - Flexible Pavements BranchJuly 24, 2008 – El Paso, TX.
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TxDOT’s Mission StatementThe mission of the Texas Department of
Transportation is to provide safe, effective and efficient movement of people and goods.
The vision of the Texas Department of Transportation is to provide transportation systems and alternatives that are comfortable, safe, durable,
cost-effective, accessible, environmentally sensitive and aesthetically appealing.
TxDOT’s Vision Statement
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General Background Information
Reflective cracking is arguably the most common distress associated with flexible pavements in Texas.
The Overlay Tester appears to be a good predictor of reflective cracking.
Asphalt Rubber mixes perform very well in the Overlay Tester
There is a lot of potential for using the Overlay Tester to improve the way we design our mixes.
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Concept over 40 years old
Used to design HMA resistant to thermal reflection cracking
Early work at Texas A&M and in Europe
Used extensively in 1980’s to study inter-layers and fabrics
Background of the Overlay Tester
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Used in NCHRP model evaluation study
TxDOT study (2001) evaluation as mix design tool
Background of the Overlay Tester
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TxDOT Overlay Tester (Tex-248-F)
Equipment Upgrades
1. Hardware and software upgrades
2. Fully computer-controlled test
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Loading Configuration
Sample - 6’’ length, 3’’ width, 1.5’’ height
Loading - Continuously triangular displacement, 5 sec loading & 5 sec unloading
Standard Test ConditionsOpening displacement - 0.025 in.Room temperature - 77 ± 3 F
Definition of failure93% Load Reduction Visible crack on surface
Fixed plate
0.08 in
Aluminum plates
150 mm (6 in)
Test Sample
Movable Plate
Ram direction
1.5 in
Displacement (in)
Time (sec)10 20
0.025
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Sample Preparation
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Sample Preparation
3 in. 6 in.3 in.
Specimen’sTop Surface
1.5 ± 0.125 in.
3 in.Specimen’sTop Surface
Cut & Discarded
Cut & Discarded
Original specimen is 6 in. diameter and ~ 2 ½ in. height.
Test specimen is ~ 3 in. wide, 6 in. length, and ~ 1 ½ in height.
Cut & Discarded
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Sample Preparation
Double Bladed Saw
Cut & Discarded
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Sample Preparation
1. Materials Epoxy Torque Wrench ¼-in Adhesive Tape Saw 10-lb Weight
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Sample Preparation
¼-in Adhesive Tape
Gluing Plates
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Sample Preparation
Specimen placed on gluing plate
10-lb weight placed on specimen
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Sample Preparation
Specimen secured to overlay tester
Completed test
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Overlay Video
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Overlay Test Software
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Field Validation Study
Crack Stops
Latex Modified Asphalt Binder
6 Month Old
Inplace Recycling10 Year Old
Section
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Field Validation Studies
1) does the test rank materials correctly ?
2) What are acceptable criteria ?
Overlay Tester Results
0
200
400
600
800
HIPR C76-22 DAC5 + L D64-22 L CM64-22CR
reps
- fa
ilure
300
700
252
520
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IH-10 Type C (PG76-22L), 4.4%AC
Hamburg Test@50C
00.5
11.5
22.5
33.5
0 5000 10000 15000 20000 25000
No. of Passes
Rut
Dep
th (m
m)
I-10
Properties Result Target
Cracking(overlay tester cycles to
failure)
2 >200
Rutting(APA rutting after 8000
cycles)
2.6 mm <6mm
RuttingHamburg
(Hamburg cycles to 0.5 inch rut)
>20K >20K
Rut resistance mix (4 in thick) placed on IH 10 in 2002 heavy traffic
Reflection cracking in 2004
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Current Completion Dates
• Rutting testing Jan. 2004• Fatigue testing (100-mm) Mar. 2006• Fatigue testing (150-mm) Dec. 2007
Two FHWA ALFs with 12 Pavement Lanes Constructed in
the Summer and Fall of 2002
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As-Built Pavement Lanes
CR-AZ----70-22
1
PG70-22Control
2
AirBlown
3
SBSLG
4
CR-TB
5
TP
6
PG70-22
+Fibers
7
PG70-22
8
SBS64-40
9
AirBlown
10
SBSLG
11
TP
12
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Lane 1
CR-AZ
300,000
Lane 2
Control
100,000
Lane 3
Air Blown
100,000
Lane 4
SBS LG
300,000
Lane 5
CR-TB
100,000
Lane 6
TP
200,000
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Percentage of Area Cracked vs. ALF Wheel Load Passes
0.0
20.0
40.0
60.0
80.0
100.0
120.0
0 50000 100000 150000 200000 250000 300000 350000
Number of ALF Passes
Perc
enta
ge o
f Are
a C
rack
ed, %
L2S3 (Control)L3S3 (Air Blown)L5S3 (CR-TB)L6S3 (Terpolymer)L4S3 (SBS LG)L1S2 (CR-AZ)
L4S3
1890
L6S3
1120L5S3
890
L2S3
60
L1S2
Did Not Crack
L3S3
80
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@ 9 years - Asphalt Rubber - PFC
Lufkin District
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Summary of Overlay Test Results
Last Update: February 2008
CST Flexible Pavements
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Overlay Test ResultsApproximately 300 mixtures have been tested.After the mix is tested 3 times, the average of the test results are entered in the database.The summary only includes data where there were more than 5 occurrences of a similar variable (mix type, aggregate type, PG binder)Test is performed until a 93% reduction or more of the maximum load measured from the first opening cycle. If 93% is not reached, the test is run to 1200 cycles.
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Influence of Mix Type Dense-Graded Hot Mix Asphalt
0
100
200
300
400
500
600
Num
ber o
f Cyc
les
Median 26 17 66 68 307Count 7 50 57 85 5Minimum 4 2 2 3 85Maximum 98 1200 461 1200 1200Average 33 115 107 205 570
Type A Type B Type C Type D Type F
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Influence of Asphalt
0
50
100
150
200
250
300
Num
ber o
f Cyc
les
Median 66 63 122 46Count 18 15 12 36Minimum 4 4 14 3Maximum 797 1138 1200 1200Average 145 229 248 179
64-22 70-22 70-28 76-22
Dense Graded Type D Mixtures Only
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Influence of Asphalt
0
100
200
300
400
500
600
Num
ber o
f Cyc
les
Median 63 177 68 76 470Count 53 80 41 88 11Minimum 2 3 3 2 14Maximum 1200 1200 1200 1200 1200Average 174 296 327 287 570
64-22 70-22 70-28 76-22 CRM
All mixtures
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Conclusions
The Overlay tester is practical and appears to be an effective predictor of HMA cracking.
The overlay tester has revealed that most TxDOT mixes are relatively susceptible to cracking.
Asphalt Rubber offers improved resistance as indicated by both field performance and the Overlay Tester
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TxDOT’s Mission StatementThe mission of the Texas Department of
Transportation is to provide safe, effective and efficient movement of people and goods.
The vision of the Texas Department of Transportation is to provide transportation systems and alternatives that are comfortable, safe, durable,
cost-effective, accessible, environmentally sensitive and aesthetically appealing.
TxDOT’s Vision Statement
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Safety
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Highway Safety
For most people, driving is the most dangerous activity that we are ever involved withBy 1950, more Americans were killed in auto accidents then were killed in both world warsA high percentage of accidents happen in intersections and in horizontal or vertical curvesWet weather accidents account for a high percentage of highway fatalities
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Highway Safety
Almost all accidents are avoidableSpeed kills…………..differential speed killsCommon attitude: “people just need to slow down and adapt to the conditions to avoid accidents”Fortunately we design highways for those that do not always do what they should
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Examples of redundant design features (features that give us a second chance)
Bridge railGuard railRumble stripsShouldersMedian barriersCrash cushionsSafety end treatments for culverts
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How Can PFC Mixes Improve Safety?
Reduces the risk of hydroplaningDrains the water off the roadway quickerReduces sprayReduces glareImproves visibility of traffic markingsCoarse macro-texture improves frictional characteristics
Question: Can we prove that these things actually reduce the occurrence of wet weather accidents?
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Type “D” Hot Mix
PFC
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DenseDense--Graded Type D vs. Permeable Friction CourseGraded Type D vs. Permeable Friction Course
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Existing concrete pavement– Relatively sound structurally (Durable)– Approximately 20 years old (Durable)– History of numerous wet weather accidents (Safety?)– Ride Quality was poor (IRI = 200) (Comfort?)– Considered to be one of the loudest pavement
surfaces around (Comfort?)
A-R PFC Overlay on CRCP IH 35 San Antonio
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A-R PFC Overlay on CRCP IH 35 San Antonio
1.5 inches of A-R PFC– Improved the ride quality of the existing CRCP by
approximately 61%– Improved the skid resistance by over 200%– Reduced the noise level by an average of 8 to 14
decibels (measured by 3 different individuals)– Significant reduction in major accidents after the PFC
overlay
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A-R PFC on CRCP
IH 35 San Antonio, Fall 2002
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Climatic & Accident Data IH 35 San Antonio: Before and After A-R PFC Overlay
July 2001-June 2002• Total Precipitation:
– 31.78 inches
• Total Days with…– Measurable precipitation: 69
• Major Accidents: 85• Major Accidents on Days
with Precipitation: 39
Nov 2003-Oct 2004• Total Precipitation:
– 32.63 inches
• Total Days with…– Measurable precipitation: 99
• Major Accidents: 48• Major Accidents on Days
with Precipitation: 19
Climate data obtained from National Oceanographic and Atmospheric Administration
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Austin District Use of PFC
First project: 2003 – US 183 Williamson Co.Second project: 2004 Emergency contract on RM 1431 in Travis Co. – “dead man’s curve”Other projects: RM 620, Lp. 360, IH 35 Travis Co., IH 35 Hays Co., US 290 etc
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Click on image below to show video
US 183 – Williamson Co.
South Bound near San Gabriel River
PFC Mix
Dense Grade (Type C)
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Click on image below to show video
RM 1431 – Travis County
WBL – Between Cedar Park and Jonestown
PFC Mix
Dense Grade
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Factors in Wet Weather Accidents (RM 1431)
Pavement was wet and slickHydroplaning coming out of a curve Vehicle slid into oncoming trafficDriver failed to control speed to avoid accidentDriver failed to adjust to roadway conditionsOther vehicle did not have time to take evasive action
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RM 1431 – Travis County – Pictures from Feb 14, 2004
2001 – 2003: 124 Total Accidents
2001 – 2003: 68 Wet Weather Accidents
2001 – 2003: 6 Fatalities, 62 Injuries (13 incapacitating)
Note: Project length is only 2 miles long
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Proactive Measures Taken by the Austin District to Reduce Accidents
Reduced speed limitIncreased police enforcement of speed limitWarning/caution signs Rumble strips & raised pavement markersOverlay with PFC in Feb. 2004Long term plan to reconstruct and straighten out curves etc.
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Safety is a Major Quality of Life Issue
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Investigations in the use of PFC for storm water quality
J. Gary LantripAustin District
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SummaryRecent accident data demonstrates that PFC mixes are effective at reducing the occurrence of wet weather accidents PFC should not be used everywhere but the use of PFC should be strongly considered in areas prone to wet weather accidents. (Undivided highways, curves, intersections)Safety is a very high priority in TxDOT’s mission and vision and the effective use of PFC mixes may have more influence on safety than previously thought PFC may also have some environmental benefits in regards to storm water runoff
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Summary• Asphalt-Rubber (A-R) is used to produce
SMAR & A-R PFC mixtures meeting TxDOT specifications.
• HMA applications using A-R help meet TxDOT’s vision of comfortable, safe, durable, and cost-effective pavements.