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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
Monday, March 25, 13
“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”
Monday, March 25, 13
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
Monday, March 25, 13
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
Monday, March 25, 13
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
Monday, March 25, 13
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
Monday, March 25, 13
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
Monday, March 25, 13
What makes a poor OT results?
• Poor aggregates• Soft (crushing)• Porous (absorptive)
• Low AC content• Stiff binders• High RAP and
RAS content
Monday, March 25, 13
What makes a poor OT results?
• Poor aggregates• Soft (crushing)• Porous (absorptive)
• Low AC content• Stiff binders• High RAP and
RAS content
Monday, March 25, 13
Balanced Mix Design Concept
Most TxDOT’s Performance Mixes Pass with easeDense graded mixes have problems (80%)
Monday, March 25, 13
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
Monday, March 25, 13
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
Monday, March 25, 13
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!!
Monday, March 25, 13
Lessons Learned & Best Practices
Design material based on required performance
High ADT/Loading with significant structure (i.e.: IH-35)
Monday, March 25, 13
Lessons Learned & Best Practices
Design material based on required performance
Low to Moderate ADT/Loading with thin
structure (i.e.: RM 32)
Monday, March 25, 13
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
Monday, March 25, 13
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
Monday, March 25, 13
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
Monday, March 25, 13
IH 40 RAP Test sectionsSummer 2009Type C Texas Gyratory Design
Fractionated RAP
Monday, March 25, 13
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
Monday, March 25, 13
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)
Monday, March 25, 13
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
Monday, March 25, 13
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!!
Monday, March 25, 13
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
Monday, March 25, 13
Manufacturers
• Shedworks College Station• Troxler • Cox and Sons (marketed thru Gilson, Jim
Bibler)
• Cost $45 to 50K
Monday, March 25, 13
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)
Monday, March 25, 13