Oklahoma DOT Perpetual

Pavement Test Sections at the

NCAT Test Track

Compression

Tension

Perpetual Pavement

Structure and materials are designed to provide a long service life (50 years +)

Early Texas Perpetual Pavements

1.5” PFC2.0” SMA

3.0” 19 mm SP

10.0” 25 mm SP

4.0” 19 mm2% air voids

6.0” crushed stone

3.0” SMA

3.0” 19 mm SP

8.0” 25 mm SP

2.0” 12.5 mm2% air voids

Waco Cotulla McAllen

10.0”, 19 mmor

25 mm SP

3.0” 12.5 mm2% air voids

1.5” PFC2.0” SMA

8.0”lime-treated

salvaged aggregate

1.5” PFC2.0” SMA

3.0” 19 mm SP

10.0” 25 mm SP

4.0” 19 mm2% air voids

6.0” crushed stone

3.0” SMA

3.0” 19 mm SP

8.0” 25 mm SP

2.0” 12.5 mm2% air voids

Waco Cotulla McAllen

10.0”, 19 mmor

25 mm SP

3.0” 12.5 mm2% air voids

1.5” PFC2.0” SMA

8.0”lime-treated

salvaged aggregate

20.5” Total HMA

16” Total HMA

16.5” Total HMA

How thick is too thick?

Cost of 5 Miles of Pavement

Assume 80’ width, $50 per ton

Save 1” in over-design: $650,000

Save 2” in over-design: $1,300,000

Save 4” in over-design: $2,600,000

How thin is too thin?

If the perpetual pavement structure is designed too thin, the risk of bottom-up cracking increases dramatically, defeating the purpose of the design and resulting in an expensive rebuild.

To design the appropriate pavement thickness, stresses and strains

Max Flexural Strain

Pavement Foundation

High ModulusRut Resistant Material

(Varies As Needed)

} 3”3”toto6”6”

High ShearHigh ShearZoneZone

1.5-3 in. PFC, SMA, etc.

To design against potential bottom-up cracking, certain strain thresholds cannot be exceeded.

Limiting Strain Theory

• Based on laboratory beam fatigue data

• “Small” strains will never induce cracking

• Limiting strain at 75 to 125 microstrains

• No bottom-up cracking below this level

These strains can be calculated based on total pavement thickness and material properties.

However, the calculations would be based on assumptions made from previously collected data.

There are large deviations in the types of environment around the country, the types of materials used and the types of pavement specified. These deviations decrease the reliability of the assumptions made to calculate strains.

If the strains could be measured directly, using Oklahoma materials and mix designs, the data would be much more reliable.

Est

imat

ed

Str

ain

National Center for Asphalt Technology (NCAT) Test Track

ODOT’S PERPETUAL PAVEMENT STRUCTURAL SECTIONS AT NCAT TEST TRACK

PLAN VIEW

SECTION N8 – 150’ SECTION N9 – 150’

25’ TRANSITION 50’ TRANSITION 25’ TRANSITION

PLAN VIEW

SECTION N8 – 150’ SECTION N9 – 150’

25’ TRANSITION 50’ TRANSITION 25’ TRANSITION

PROFILE VIEW

2” SMA w/PG 76-28

3” SuperPave 19.0mm w/PG 76-28

3” SuperPave 19.0mm w/PG 64-22

3” SuperPave 19.0mm w/PG 64-22 2” RBL w/PG 64-22

3” RBL w/PG 64-22

*RBL = RICH BOTTOM LAYER

ODOT’S PERPETUAL PAVEMENT STRUCTURAL SECTIONS AT NCAT TEST TRACK

Structural Study Test Sections

0.0

2.0

4.0

6.0

8.0

10.0

12.0

14.0

16.0

18.0

20.0

22.0

24.0

N1 N2 N3 N4 N5 N6 N7 N8 N9 N10 S11

As

Bu

ilt T

hic

kne

ss, i

n.

PG 67-22 PG 76-22 PG 76-22 (SMA) PG 76-28 (SMA)

PG 76-28 PG 64-22 PG 64-22 (2% Air Voids) PG 70-22

Limerock Base Granite Base Type 5 Base Track Chert Soft Subgrade

Florida Alabama & FHWAOklahoma

FHWAMissouri Alabama

Max Flexural Strain

Pavement Foundation

High ModulusRut Resistant Material

(Varies As Needed)

1.5-3 in. PFC, SMA, etc.

The maximum flexural strain is directly measured using a series of strain gauges installed at the bottom of the asphalt section.

MIC

RO

ST

RA

IN

10” 14” 16”

?

If we have determined the strain for a 10” and 14” thick pavement, the thickness at the critical strain level can be interpolated / extrapolated

Instrumentation – N8

-12

-10

-8

-6

-4

-2

0

2

4

6

8

10

12

-12 -10 -8 -6 -4 -2 0 2 4 6 8 10 12

Tranverse Offset from Center of Outside Wheelpath, ft

Lon

gitu

din

al O

ffse

t fr

om C

ente

r of

Arr

ay, f

t .

Earth Pressure CellAsphalt Strain Gauge

Edge StripeOutside WheelpathInside WheelpathCenterline

Direction of Travel

Temperature probe

Laser

1 2 3

4 5 6

7 8 9

10 11 12

13

14

15

Accelerated Loading

• Compress 10-15 years into 2 years

• Heavy triples optimize safety and efficiency

• Each axle loaded to federal legal bridge limit

• Heavier loads induce unrealistic damage

• No bridge spans to overload on NCAT track

• Average gross vehicle weight 155k pounds

Long Term Response Measurements

• Weekly - three passes of 5 trucks– Steer axle (12 kip), tandem (40 kip), 5 single axles (20

kip/axle)– 45 MPH

• Measure strain• Measure pressure• Measure temps• Characterize long-term trends in strain response

Transverse Strain

-10

0

10

20

30

40

50

60

70

80

90

0 0.5 1 1.5 2 2.5 3

Time (sec)

Mic

ro S

trai

n

To design the appropriate pavement thickness, stresses and strains

Max Flexural Strain

High ModulusRut Resistant Material

(Varies As Needed)

Vertical Compressive Strain

1.5-3 in. PFC, SMA, etc.

The vertical compressive strain is directly measured using pressure plates installed at the top of the subgrade.

Moisture sensors were also placed in the subgrade to continuously monitor soil conditions

Temperature probes were placed in the pavement to continuously monitor temperature at various depths

A datalogger is used to collect information from the different pavement sensors.

In addition to the normal “slow speed” mode that continuously gathers data, a “high speed” mode can be used to collect 40,000 data points per second.

Additional Testing - Surface Map Cracking

3/21/2005N2

0

1

2

3

4

5

6

7

8

9

10

11

1225 30 35 40 45 50 55 60 65 70 75 80 85 90 95 100 105 110 115 120 125 130 135 140 145 150 155 160 165 170 175

Longitudinal Distance from Far End of Section (ft)

Tran

sver

se D

ista

nce

from

Cen

terl

ine

(ft)

0

1

2

3

4

5

6

7

8

9

10

11

12

Thic

knes

s of

Exp

erim

enta

l Pav

emen

t Lift

s (in

)

Cracking Coring Random Testing Avg Wheelpaths Gauge Array Avg Thickness

FWD Testing

Rut Testing

Skid Testing

Inertial Profiler –RuttingSmoothnessSurface Texture

N8 and N9 – Strain vs. Date

0

200

400

600

800

1000

120011

/1/2

006

12/1

/200

6

12/3

1/20

06

1/30

/200

7

3/1/

2007

3/31

/200

7

4/30

/200

7

5/30

/200

7

6/29

/200

7

7/29

/200

7

8/28

/200

7

9/27

/200

7

10/2

7/20

07

11/2

6/20

07

12/2

6/20

07

1/25

/200

8

Date

Lo

ng

itu

din

al M

icro

stra

in

0

1

2

3

4

5

6

Rat

io o

f S

trai

n (

N8/

N9)

N8 (Meas)

N9 (meas)

Ratio (N8 / N9)

Average Ratio (N8/N9) = 2.6

Effect of Depth (N9)

0

50

100

150

200

250

300

350

10/10/2006 11/29/2006 1/18/2007 3/9/2007 4/28/2007 6/17/2007 8/6/2007 9/25/2007 11/14/2007 1/3/2008 2/22/2008

Date

Lo

ng

itu

din

al M

icro

stra

in

Bottom of HMA

Bottom of Lift 2

Bottom of Lift 3

Temperature Normalized Response

0

50

100

150

200

250

300

350

400

Averageof N1

Averageof N2

Averageof N4

Averageof N6

Averageof N7

Averageof N8

Averageof N9

Averageof N10

Averageof S11

Mic

rost

rain

s

Normal Operations• 55% of Strains below threshold

0

20

40

60

80

100

120

140

10/10/2006 12/24/2006 3/9/2007 5/23/2007 8/6/2007 10/20/2007 1/3/2008 3/18/2008

Date

Tem

per

atu

re (

oF

)

0

100

200

300

400

500

600

700

Mic

rost

rain

T2_AVG

Strain

-12

-10

-8

-6

-4

-2

0

2

4

6

8

10

12

14

16

18

20

22

24

26

28

30

-12 -10 -8 -6 -4 -2 0 2 4 6 8 10 12

Tranverse Offset from Center of Outside Wheelpath, ft

Lon

gitu

din

al O

ffse

t fr

om C

ente

r of

Arr

ay, f

t

Earth Pressure CellAsphalt Strain Gauge

Gauges 16 - 19Top of HMA Lift 1

Gauges 20 - 23Top of HMA Lift 2

Gauges 24 - 27Top of HMA Lift 3

Gau

ges

Nu

mb

ered

16

- 27

Edge StripeOutside WheelpathInside WheelpathCenterline

Direction of Travel

Laser

N9 Instrumentation(Multi-Depth Array)

Supplemental FHWA

Experiment

N9 Cross Section and Supplemental Instrumentation

0

1

2

3

4

5

6

7

8

9

10

11

12

13

14

15

De

pth

, in

.

Full Depth HMA Section

Asphalt Strain Gauge

Thermistor

SMA

PG 76-28

PG 64-22

PG 64-22

PG 64-22Rich Bottom

Asphalt Strain GaugePlan View

OWPCL

Strain vs. Speed and Temperature (ODOT and FHWA)

• Primary Objectives– Study a perpetual pavement under a wider set

of conditions• Primarily look at speed and temperature effects

Data Collected

• 4 Speeds Tested– 15-45 mph (10 mph increments)

• 4 Dates– April – May 2007

• Measured– Temperature– Tensile Strain

Investigations

• Studied relationships– Speed-Strain– Temperature-strain– Combined

• Strain Threshold

• Load Durations– Relate to Frequency

Relationships

• Speed-Strain– Strain at bottom of HMA– Decrease with speed

• Temperature-Strain– Strain at bottom of HMA– Increase with temperature

bva ln dTce

deva cT lnR2: 0.955-0.986

Strain Threshold

• Tensile strain threshold: 100με

0

100

200

300

400

500

600

700

20 40 60 80 100 120 140

Temperature

Mic

rost

rain

15 mph

25 mph

35 mph

45 mph

65 mph

Strain Threshold

THANK YOU!

QUESTIONS?