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Update on the Texas Overlay Tester

Cindy Estakhri, Texas Transportation InstituteDale Rand, TxDOT

Tom Scullion, Fujie Zhou, Lubinda Walubita

Monday, March 25, 13

Update on the Texas Overlay Tester

Hamburg Wheel Tracking Device Overlay Tester


“Since the completion of the SHRP program with the introduction of the PG grading system most states have been searching for practical performance related tests which can be run at the mix design stage

Many states have implemented rutting and moisture susceptibility test; with the Hamburg and APA being widely used

No states have adopted a repeated load cracking test

The Texas Overlay tester is one such cracking test - it is being included in many of TxDOT’s 2013 specifications

The need for a cracking test has never been more critical with the move towards increased use of recycled materials”


Overlay Tester Background• Concept over 40 years old• Early work at Texas A&M and Europe• Simulates reflection cracking from thermal movements • Used extensively in 1980’s to study inter-layers and fabrics• TxDOT study (2002) used to investigate failure


The Overlay Tester (OT) Tex Method 248-F

Room temp 25 C0

10 second cycle

0.025 inch opening

7% air voids

In Texas Specs OT ≥ 200 SMA

> 750 CAM >500 TOM

.025 inch (0 s/cycle

Measures load, number of cycles, time, etc


http://images.google.com/imgres?imgurl=www.chem.tamu.edu/services/NMR/images/atm.gif&imgrefurl=http://www.chem.tamu.edu/services/NMR/instruments.shtml&h=288&w=303&prev=/images%253Fq%253Datm%252Btamu%2526svnum%253D10%2526hl%253Den%2526lr%253D%2526ie%253DUTF-8%2526oe%253DUTF-8%2526sa%253DG






IH-10 Type C (PG76-22L), 4.4%AC

0

0.7500

1.5000

2.2500

3.0000

0 7500 15000 22500 30000

Hamburg Test@50C

Rut

Dep

th (m

m)

No. of Passes

I-10

Properties Result Target

Cracking(overlay tester cycles to failure)

2 >300

Rutting(Hamburg cycles to 12.5mm rut)

2.9 mm at 20K

>20K

Rut resistance mix (4 in thick) placed on IH 10 in 2002 very heavy traffic


Field Validation Studies 2003 Overlays over cracked pavements

0

175

350

525

700

HIPR C76-22 DAC5 + L D64-22 L CM64-22 CR

77 Deg F 25 mils opening

reps

- fa

ilure

300US 175

700IH 20

25SH 3

2US 84

520US 281

2 months1 Year

10 years


Validation Studies FHWA-ALF

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

189K

110K

270K

56K 50K

50

18001100

850

35


What makes a poor OT results?

• Poor aggregates• Soft (crushing)• Porous (absorptive)

• Low AC content• Stiff binders• High RAP and

RAS content


Balanced Mix Design Concept

Most TxDOT’s Performance Mixes Pass with easeDense graded mixes have problems (80%)


14

Laredo District−Loop 20 (1 mile)−Spur 400 (1 mile)−US 59 (3 mile)

Heavily trafficked Urban Roads Slow < 30 mph

Implementation of the Balance Mix Design Concept

Project 6132 Monday, March 25, 13

15

Lab Test Results

Lubinda

Original ⇒ PG 70-22 (The TGC Method)

Modified ⇒ PG 64-22 (The TTI BMD Method)

HWTT & OT testing ⇒ @ 7±1% AV


http://images.google.com/imgres?imgurl=www.chem.tamu.edu/services/NMR/images/atm.gif&imgrefurl=http://www.chem.tamu.edu/services/NMR/instruments.shtml&h=288&w=303&prev=/images?q=atm+tamu&svnum=10&hl=en&lr=&ie=UTF-8&oe=UTF-8&sa=G






TTI Test Section# LRD01Laredo; Spur 400, WB 5.0% PG 64-22 + Crushed Gravel + 20% RAPTTI HMA Mix-Design (Project 0-6132)2” thick overlay, 1 mile longPicture date = June 26, 2012Construction date: Aug 2010

TTI BMD MethodHWTT = 6.0 mm after 20 000 passes

OT = 200 cycles

Spur 400


TTI Test Section# LRD01Laredo; Spur 400, WB 5.0% PG 64-22 + Crushed Gravel + 20% RAPTTI HMA Mix-Design (Project 0-6132)2” thick overlay, 1 mile longPicture date = June 26, 2012Construction date: Aug 2010

TTI BMD MethodHWTT = 6.0 mm after 20 000 passes

OT = 200 cycles

Spur 400

Before!!


Lessons Learned & Best Practices



Design material based on required performance




High ADT/Loading with significant structure (i.e.: IH-35)




Low to Moderate ADT/Loading with thin

structure (i.e.: RM 32)


Impact of RAP and RAS on Lab TestsType D Mix Paris District

RAP % RAS % Hamburg Test(< 12.5 mm)

Overlay Test IDT

0 0 4.3 123 145

15 0 3.9 70 155

0 5 3.0 20 141

15 5 1.5 5 214

Binder

$ Ton64-2

2575

70-22

68476-2

2727

64-28

684

Work underway with softer binders especially xx-28 and xx-34Overlay Tester results from MnRoad Mixes encouraging

Challenges Opportunities

Add binderChange Binder


Amarillo RAP test sections

RAP improves rutting test results makes cracking results worse

Experimental test sections on IH40:•0% RAP section: Control section•20% RAP section: TTI designed

•35% RAP section: TTI designed


Summary of RAP mix design

Section

RAP (%)

Virgin binder

Designer Mix design approach

AC (%)

Hamburg rut depth @20000

OT cycles

0 20 PG64-28 Contractor

Item 340-Type C

5.0 3.72 10

1 0 PG64-28 Contractor

Item 340-Type C

4.8 4.38 50

2 35 AC-10 (PG58-28)

TTI Balanced mix design

5.5 8 mm 200

3 20 PG64-28 TTI Balanced mix design

5.3 7.4 mm 125


IH 40 RAP Test sectionsSummer 2009Type C Texas Gyratory Design

Fractionated RAP


Reflection Cracking Rate (%) Sections 8/11/20

094/22/201

09/8/2010 4/5/2011 OT

cycles20% RAP-contractor

0 0 34 87 100% RAP-

contractor0 0 18 55 50

35% RAP-TTI 0 0 0 27 200

20% RAP-TTI 0 0 4 54 125


Another validation of 300 cycles


Challenges to Implementation of OTAddressed in study 6607

• Need to improve Repeatability– All repeated load cracking tests have variability issues– Problems found in first between lab round robin– Study recommended improvements to

• test procedure 248 F• Improve equipment calibration procedures

– Conduct second Round Robin Test• Makes Mix design more challenging

– Some aggregates/asphalt combinations will not work– Major challenge with high RAP/RAS mixes

• Where When and how to apply OT criteria– What numbers to use

• For different mixes (surface, base)• For Different pavements (Jointed Concrete, CTB, Flex, CRCP)


Sources of Variation in Current OT protocol

• Need to calibrate and Standardize equipment

• Double Crack initiation

• Method of drying sample

• Age of sample at time of test

• Number of samples to test


Double Crack Initiation 1 sample in 15

cracks


30

OT Tex-248-F: Replicate Samples - Analysis

Lubinda

20

2225

28

119

83

92 96

538

645

527

600

Analysis: –Best 3 or 2 out of 5 seems to give reasonable variability (COV) without significantly affecting the OT cycles.–Challenge is the amount of work involved and material requirement especially with the current 4.5 inches sample mold height!!








Results from 6 OT machines in Texas (3 Districts, CST, TTI and PaveTex)


32

Extract From TxDOT’s Overlay Tester Data base

Dale Rand and Gisel Carasco


Other OT Users

• New Jersey– Implemented in NJ 2012 Spec for high RAP/RAS

mixes– Requires 150 cycles

• Massachusetts (Dr W. Mogawer)• Nevada (Reno)• NCAT• City of Portland Oregon

– In 2013 specs


Manufacturers

• Shedworks College Station• Troxler • Cox and Sons (marketed thru Gilson, Jim

Bibler)

• Cost $45 to 50K


Implementation within TxDOT

• Updated Test Method Tex 248-F • ASTM WK 26816 (under review)• As of 2013 the OT is included in the

following TxDOT Specs– SMA > 200 cycles– Fine Graded PFC > 300 cycles– Thin Overlay Mix > 500 cycles– HIPR 150 cycles ( 2 projects underway

right now)


Wording in Current Specs


Thank you!

[email protected]


mailto:[email protected]

mailto:[email protected]

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