Durability & Safety Advantages

of Asphalt Rubber Pavements

Dale A. Rand, P.E. – TxDOT

Director - Flexible Pavements BranchJuly 24, 2008 – El Paso, TX.

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

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.

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

Used in NCHRP model evaluation study

TxDOT study (2001) evaluation as mix design tool

Background of the Overlay Tester

TxDOT Overlay Tester (Tex-248-F)

Equipment Upgrades

1. Hardware and software upgrades

2. Fully computer-controlled test

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

Sample Preparation

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

Sample Preparation

Double Bladed Saw

Cut & Discarded

Sample Preparation

1. Materials Epoxy Torque Wrench ¼-in Adhesive Tape Saw 10-lb Weight

Sample Preparation

¼-in Adhesive Tape

Gluing Plates

Sample Preparation

Specimen placed on gluing plate

10-lb weight placed on specimen

Sample Preparation

Specimen secured to overlay tester

Completed test

Overlay Video

Overlay Test Software

Field Validation Study

Crack Stops

Latex Modified Asphalt Binder

6 Month Old

Inplace Recycling10 Year Old

Section

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

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

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

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

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

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

@ 9 years - Asphalt Rubber - PFC

Lufkin District

Summary of Overlay Test Results

Last Update: February 2008

CST Flexible Pavements

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.

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

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

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

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

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

Safety

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

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

Examples of redundant design features (features that give us a second chance)

Bridge railGuard railRumble stripsShouldersMedian barriersCrash cushionsSafety end treatments for culverts

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?

Type “D” Hot Mix

PFC

DenseDense--Graded Type D vs. Permeable Friction CourseGraded Type D vs. Permeable Friction Course

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

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

A-R PFC on CRCP

IH 35 San Antonio, Fall 2002

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

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

Click on image below to show video

US 183 – Williamson Co.

South Bound near San Gabriel River

PFC Mix

Dense Grade (Type C)

Click on image below to show video

RM 1431 – Travis County

WBL – Between Cedar Park and Jonestown

PFC Mix

Dense Grade

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

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

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.

Safety is a Major Quality of Life Issue

Investigations in the use of PFC for storm water quality

J. Gary LantripAustin District

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

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.