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Evaluating Structural Performance of Base/Subbase Materials at the Louisiana Accelerated Pavement Research Facility

Zhong Wu, Ph.D., P.E.Zhongjie Zhang, Bill King

Louay Mohammad

Outline

• Background• Objectives• Project Layout and Instrumentation• Discussion of Results• Conclusions

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BackgroundBlended Calcium Sulfate (BCS) material is– by-product from hydrogen fluoride production – used as base materials in Louisiana low-volume roads.

When raw BCS materials is used, the major engineering concern– water susceptibility

A previous laboratory study at LTRC indicates that– The water susceptibility of BCS materials can be improved by

mixing with granulated ground furnace slag, flyash, cement and etc.

– In fact, 10% slag (by weight) stabilized minus 4 BCS materials showed significant improvement on both water susceptibility and strength

However, field performance of stabilized BCS base materials is unknown

Background (contd..)In-place cement- or lime- treated soil subgrade– normally 12” thick– used in wet conditions of pavement construction in

LouisianaThe treated subgrade– contains 4 to 10% cement or lime by volume – considered as a “working table” in pavement design

• no structure value assignedHowever, Laboratory results indicated cement treated soils showed significantly higher modulus and strength than lime-treated soilsCan cement-treated soil be considered as a subbase layer and provide certain structure value in a pavement design?

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Objective

• To evaluate the structural performance of thin flexible pavements containing different chemically stabilized base and subbasematerials under accelerated loading.

LouisianaAccelerated Loading Facility (ALF)

• Approximately 100-ft long and 55-ton • One half of a single axle• Load adjustable from

– 9,750 lbs ~ 18,950 lbs – Simulate traffic wander

• Speed - 10.5 mile per hour• Operated by

– Pavement Research Facility (PRF) in Port Allen, LA

Tire Pressure = 105 psi

Total Load = 9,750 lbs

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Pavement Structures

2 in.

8.5 in.

12 in.

19 mm Superpave Mixture 19 mm Superpave Mixture

BCS/Slag Base BCS/Flyash Base

Lime-treated Soil Subbase Lime-treated Soil Subbase

2 in.

8.5 in.

12 in.

19 mm Superpave Mixture

Foamed Asphalt Base I

Cement-treated Soil Subbase

2 in.

8.5 in.

12 in.

19 mm Superpave Mixture

Foamed Asphalt Base II

Cement-treated Soil Subbase

2 in.

8.5 in.

12 in.

19 mm Superpave Mixture 19 mm Superpave Mixture

Crushed Stone Base Crushed Stone Base

Lime-treated Soil Subbase Cement-treated Soil Subbase

Section 1

Section 4

Section 2

Section 5

Section 3

Section 6

Pavement Materials

• Hot Mix Asphalt (HMA) mixture• Stabilized BCS materials• Foamed asphalt stabilized materials• Lime or cement treated soil materials• Subgrade soils

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HMA Mixture• 19-mm Superpave Level –II mixture• Polymer-modified PG 76-22

– Supplied by Marathon– Optimum binder content: 4.4%

• Aggregate blend– 45.4% #67 coarse granite aggregate, – 17.1% #11 crushed siliceous limestone, – 10.3% coarse sand, – 12.9% crushed gravel, and – 14.3% reclaimed asphalt pavement (RAP).

Stabilized BCS Base Materials• Section 1

– BCS stabilized with the grade 120 ground granulated blast furnace slag (GGBFS) – 10% by volume

• Section 2– BCS stabilized with Class C flyash (15% by volume)

0102030405060708090

100

0.010.1110100

Particle Diameter (mm)

Perc

ent F

iner

(%

Raw BCSBCS-Fly ashBCS-GGBFS

BCS/GGBFSSection 1

BCS/flyashSection 2

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Foamed Asphalt Base• Foamed asphalt (FA) process

– When cold water injected into the hot asphalt, it turns to steam:

• contains thousands of tiny asphalt bubbles • causes the asphalt expands many times in volume• decreases the binder viscosity.

• Section 3 is a FA stabilized base – Design Standard “Wirtgen Cold Recycling Manual”– Components

• 2.8% PG 58-22 asphalt binder – 3% water

• 48.6% RAP, and • 48.6% recycled soil cement

Subbase and Subgrade• Subbase Materials:

– in-place lime treated soils (10 % by volume)• Sections 1 & 2

– in-place cement treated soils (8 % by volume)• Section 3

• Soil Properties

A-6CL-ML17.118.5123160.323.591

AASHTOUSCS

Classificationγd

(kN/m3)Wopt(%)PILL(%)Silt

(%)Clay (%)

Passing# 200 (%)

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Resilient Modulus Test• AASHTO T-307-99• Constitutive soil model (new M-E design guide)

195-0.560.382200Foam asphalt605-0.300.225950BCS-Flyash850-0.080.278114BCS-Slag408-1.790.646761Cement-treated soil138-2.920.231445Lime-treated soil38-3.040.30692Subgrade soil

Mr (Mpa)k3k2k1Material

Instrumentation & Field Data Collection

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Instrumentation Control

• Data Acquisition Hardware– MEGADAC 3415AC– Up to 25,000 samples per

second

• Data Acquisition Software– TCS Windows– 1,000 samples per

second

107.5 ft0+52.5 0+57.0

2” HMA

12” Subbase

Base Pressure CellSubbase Pressure Cell

8.5” Base

Multi Depth Deflectometer

D1

D5

D4

D6

D3

D2

Field Instrumentation Layout

Plan View

Vertical View

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Earth Pressure Cell

• Geokon model 3500– Hydraulic type– 9 in. diameter– 5 lbs– designed to measure

total pressure in earth fills up to 100psi

Typical Pressure Cell Readings Under Wheel Loading

• Pressure cell response signals are slightly different due to different base and subbase materials

• Generally subbase cell picks up load earlier than base cell

Lane 4-1A Lane 4-2A

Lane 4-3A Base

Subbase

Subbase

Subbase Base

Base

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Multi-Depth Deflectometer (MDD)

• SnapMDD– Construction Technology

Laboratories, Inc. Illinois• Measure

– compressively elastic & plastic deformations

– up to seven depths• Installation

– bore hole – 5-in in diameter– 10-ft deep

Typical MDD Potentiometer Readings

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NDT Tests• Dynatest 8002 model FWD

– 9 sensors (0, 8, 12, 18, 24, 36, 48, 60, 72”)– Every 25,000 repetitions

• Dynaflect– 1,000-lb dynamic load – 5 geophones at 1 ft interval– Every 25,000 repetitions

ALF Loading & Condition• 9,750-lbs for 175,000 passes

– Equivalent to 241,039 ESALs• 12,050-lbs from 175,000 to 225,000

passes– Equivalent to 401,713 ESALs

• Un-controlled in situ environment– Testing period from Oct. – Aug.– Air temperature from 30 to 93 oF– Total rainfalls – only 16.8 inches

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Field Test Results

Average Measured Rut Depths

0

2

4

6

8

10

12

14

0 50000 100000 150000 200000 250000 300000 350000 400000 450000

Load (ESALs)

Rut

Dep

th (m

m)

section 1section 2section 3

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Instrumentation Results

Measured Vertical Stresses

σv1=5.0psi

σv2=1.7psi

HMABCS/Flyash

LimeSoil

Subgrade

S2

σv1=0.8psi

σv2=0.5psi

HMABCS/Slag

LimeSoil

Subgrade

S1

σv1=10.2psi

σv2=0.4psi

HMAFoamAsphalt

CementSoil

Subgrade

S3

9,750 lb9,750 lb 9,750 lb

9,750 lb 12,050 lb

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Measured Vertical Stresses (Contd..)

σv1=? psi

σv2=2.5psi

HMABCS/Flyash

LimeSoil

Subgrade

S2

σv1=0.9psi

σv2=0.6psi

HMABCS/Slag

LimeSoil

Subgrade

S1

σv1=12.4psi

σv2=0.8psi

HMAFoamAsphalt

CementSoil

Subgrade

S3

12,050 lb12,050 lb 12,050 lb

MDD Results (Elastic Deformation)-0.1

0.0

0.1

0.2

0.3

0.4

0.5

0.6

23.8 23.9 23.9 24.0 24.0 24.1 24.1 24.2 24.2

Time, seconds

MD

D D

ispl

acem

ents

, mm

MDD1MDD2MDD3MDD4

MDD5MDD6

0

400

800

1200

1600

2000

2400

2800

0 0.1 0.2 0.3 0.4 0.5 0.6

Deflection (mm)

Dep

th (m

m)

Section 1Section 2Section 3

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MDD Results (Plastic Deformation)MDD on Section 2

0

3

6

9

12

15

0 100000 200000 300000 400000 500000Load (ESALs)

Perm

anen

t Def

orm

atio

n (m

m)

BCS/flyashlime-treatedSubgrade

MDD on Section 3

0

3

6

9

12

15

0 100000 200000 300000 400000 500000

Load (ESALs)

Perm

anen

t Def

orm

atio

n (m

m) Foam Asphalt

Cement-treatedSubgrade

Kinchen and Temple in 1980 developed Dynaflect-deflection based approach for structural evaluation of flexible pavements

1.0

2.0

3.0

4.0

5.0

6.0

0 100000 200000 300000 400000 500000

ESALs

Stru

ctur

e N

umbe

r (SN

)

Section 1 Section 2 Section 3

Dynaflect Results (SN)

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FWD Results

0.0

0.2

0.4

0.6

0.8

1.0

0 100000 200000 300000 400000 500000

ESALs

D0 a

t 25C

(mm

)

Section 1 Section 2 Section 3

0

10

20

30

40

50

60

70

80

0 100000 200000 300000 400000 500000

ESALs

Spre

adab

ility

(%)

Section 1 Section 2 Section 3

8” 4” 6” 6” 12” 12” 12” 12”

d0 d1 d2 d3 d4 d5 d6 d7 d8

FWD Load

d0 (mm) Spreadability (%)

Spreadability, percentD

dddddSp 1005 0

65420 ××

++++=

M-E PDG Predicted Rut Depths

0

2

4

6

8

10

12

14

0 100000 200000 300000 400000 500000

ESALs

Rut

Dep

th (m

m)

section 1(measured)

section 2 (measured)

section 3(measured)

section 1(M-E PDG predicted)

section 2(M-E PDG predicted)

section 3(M-E PDG predicted)

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Model Predicted Rut Depths

0

2

4

6

8

10

12

14

0 100000 200000 300000 400000 500000

ESALs

Rut

Dep

ths

(mm

)section 1(measured)

section 2 (measured)

section 3(measured)

section 1(Eq.4 predicted)

section 2(Eq.4 predicted)

section 3(Eq.4 predicted)

Rutting Prediction Modelγβ

α⎟⎟⎠

⎞⎜⎜⎝

⎛×⎟

⎟⎠

⎞⎜⎜⎝

⎛××=

iresf EE

resprespMNADamage

5293.31433.201663.0

%803.008.5)( ⎟⎟

⎠

⎞⎜⎜⎝

⎛×⎟

⎠⎞

⎜⎝⎛××= pS

mmD

MNmmmmDepthRut

MN = 1 million load applications,resp = pavement response (e.g. stress or strain),respref = reference response.E = modulus,Ei = initial modulus, andA,α, β, χ = model constants.

(n=212, R2=0.89)

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Forensic Investigation (Section 3)

Trenching

Forensic Investigation (contd..)

• Three auger holes were drilled on each test section. The average moisture content for the foam-asphalt base materials was 8.7 %– As-built moisture content was 10.1%

• DCP results showed that the average mm per blow was 0.3, 1.1, and 3.0 for BCS/slag, BCS/flyash, and FA bases, respectively.

• Design specification requires only 300 kpa (43 psi) of ITS-Dry and 150 kpa (22 psi) of ITS-Wet for the FA base mixture design– Seems too low to sustain the shear force under ALF

loading

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Conclusions• The BCS/Slag base material performed significantly better

than its counterpart material - BCS/Flyash, whereas BCS/flyash better than foam-asphalt base.

• The cement-treated subbase possessed higher load-induced structural capacity than the lime-treated subbase, in terms of– higher resilient modulus, greater load carrying capability,

and smaller permanent deformation . • A heavier load would cause higher percent increase of vertical

stresses on top of the subgrade than upper pavement layers.• The M-E PDG software generally overestimated the rut

depths developed in the three test sections of this study• The proposed model, which relates flexible pavement rutting

development to the in-situ surface deflection characteristics, has a potential to be directly utilized in a mechanistic-empirical pavement design and analysis.

Questions?

Acknowledgment

• Financial Support is provided by – Louisiana Transportation and

Development (LaDOTD)– Louisiana Transportation Research

Center (LTRC)