Center for Earthworks Engineering Research

A Comparison of Pavement Foundation Stabilization TechnologiesPeter J. Becker, M.S.

Graduate Research Assistant

Center for Earthworks Engineering Research (CEER)

pbecker@iastate.edu

David J. White, Ph.D., P.E.

Associate Professor and holder of Richard L. Handy Professorship

Director, Center for Earthworks Engineering Research (CEER)

Department of Civil, Construction and Environmental Engineering

Iowa State University

djwhite@iastate.edu

Center for Earthworks Engineering Research 2

This presentation will compare the performance of different pavement foundation stabilization techniques used at the Central Iowa Expo (CIE) roadway reconstruction• Project overview• Performance (as constructed, freeze-thaw, &

recovering)• Cost analysis

Center for Earthworks Engineering Research 3

The testing area encompasses 24 test sections distributed over 12 north-south roads

Center for Earthworks Engineering Research 4

Prior to reconstruction, each test section comprised the following cross section

GRANULAR BASEA-1-a (SM)

SUBGRADEA-6(5) (CL)

BIAXIAL GEOGRID

Existing Profile

CHIPSEALCOATING

8”

Center for Earthworks Engineering Research 5

Roadways were reconstructed with different pavement foundation stabilization techniques• Control• Mechanical stabilization of subgrade (Mix A-1-a with A-6(5))• Geocell-reinforced subbase (4 in. and 6 in.)• Geotextile fabric (non-woven and woven)• Polymer grid (biaxial and triaxial)• 5% cement stabilized subbase• 5% cement and 0.4% fiber stabilized subbase

• Fibrilated polypropylene (FP) and monofilament polypropylene (MP) fibers

• Recycled subbase• 10% cement (PC) stabilized subgrade• 10%, 15%, and 20% fly ash (FA) stabilized subgrade• High Energy Impact Compaction (Converted to control section)

Center for Earthworks Engineering Research 6

Performance was measured using the following in situ testing equipment

Falling Weight Deflectometer (FWD)Dynamic Cone Penetrometer (DCP)

Center for Earthworks Engineering Research 7

Mechanical stabilization of subgrade is the mixture of good quality geomaterial with poor quality subgrade

Particle Diameter (mm)

0.0010.010.1110100

Per

cent

fin

er (

%)

0

20

40

60

80

100

SubgradeReclaimed SubbaseMechanically Stabilized Subgrade (Average)Mechanically Stabilized Subgrade

Control Mech. Stab.

Ave

rage

Sub

base

Mod

ulus

, E

SB

-FW

D (

psi)

0

5000

10000

15000

20000July 2012 (shortly after stabilization)October 2012April 2013 (after spring-thaw)May 2013

Control Mech. Stab.

Ave

rage

Cal

iforn

ia b

earin

gra

tio in

sub

grad

e or

recy

cled

sub

base

, CB

RS

G/R

SB

1

10

100July 2012 (shortly after stabilization)October 2012April 2013 (after spring-thaw)May 2013

Center for Earthworks Engineering Research 8

Geocells use confinement to strengthen geomaterials

Control 4 in. Geocell 6 in. Geocell

Ave

rage

Sub

base

Mod

ulus

, E

SB

-FW

D (

psi)

0

5000

10000

15000

20000July 2012 (shortly after stabilization)October 2012April 2013 (after spring-thaw)May 2013

Control 4 in. Geocell 6 in. Geocell

Ave

rage

Cal

iforn

iabe

arin

g ra

tio in

mod

ified

subb

ase,

CB

RM

SB

10

100

1000July 2012 (shortly after stabilization)October 2012April 2013 (after spring-thaw)May 2013

Center for Earthworks Engineering Research 9

Geotextile fabrics provide separation and filtration for pavement layers

Control Non-Woven Woven

Ave

rage

Sub

base

Mod

ulus

, E

SB

-FW

D (

psi)

0

5000

10000

15000

20000July 2012 (shortly after stabilization)October 2012April 2013 (after spring-thaw)May 2013

Control Non-Woven Woven

Ave

rage

Cal

iforn

iabe

arin

g ra

tio in

mod

ified

subb

ase,

CB

RM

SB

10

100

1000July 2012 (shortly after stabilization)October 2012April 2013 (after spring-thaw)May 2013

Woven Geotextile Fabric

Non-woven Geotextile Fabric

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Polymer grids provide planar reinforcement to pavement layers

Control Biaxial Triaxial

Ave

rage

Sub

base

Mod

ulus

, E

SB

-FW

D (

psi)

0

5000

10000

15000

20000July 2012 (shortly after stabilization)October 2012April 2013 (after spring-thaw)May 2013

Control Biaxial Triaxial

Ave

rage

Cal

iforn

iabe

arin

g ra

tio in

mod

ified

subb

ase,

CB

RM

SB

10

100

1000July 2012 (shortly after stabilization)October 2012April 2013 (after spring-thaw)May 2013

Center for Earthworks Engineering Research 11

Axial Strain (in/in)

0.00 0.02 0.04 0.06 0.08 0.10 0.12 0.14 0.16

Dev

iato

r S

tres

s (p

si)

0

100

200

300

400

Unconfined Compressive Strength Test:2.5% Cement, 0.6% FP Fibers

Cement stabilization (of subbase) increases strength and stiffness. Fiber stabilization increases toughness, shear strength.

Control PC PC + FP Fiber PC + MP Fiber

Ave

rage

Sub

base

Mod

ulus

, E

SB

-FW

D (

psi)

0

10000

20000

30000

40000

50000July 2012 (shortly after stabilization)October 2012April 2013 (after spring-thaw)May 2013

Control PC PC + FP Fiber PC + MP Fiber

Ave

rage

Cal

iforn

ia b

earin

gra

tio in

sub

grad

e or

recy

cled

sub

base

, C

BR

SG

/RS

B

1

10

100

1000

10000July 2012 (shortly after stabilization)October 2012April 2013 (after spring-thaw)May 2013

All

May

201

3 D

CP

s re

ache

dre

fusa

l with

in M

SB

laye

r

FP Fibers MP Fibers

Center for Earthworks Engineering Research 12

Recycled subbase test section included 6 in. nominal subbase below modified subbase layer

Control Rec. Subbase

Ave

rage

Sub

base

Mod

ulus

, E

SB

-FW

D (

psi)

0

5000

10000

15000

20000

25000

30000July 2012 (shortly after stabilization)October 2012April 2013 (after spring-thaw)May 2013

Control Rec. Subbase

Ave

rage

Cal

iforn

ia b

earin

gra

tio in

sub

grad

e or

recy

cled

sub

base

, C

BR

SG

/RS

B

1

10

100

1000July 2012 (shortly after stabilization)October 2012April 2013 (after spring-thaw)May 2013

Center for Earthworks Engineering Research 13

Cement stabilization (of subgrade) increases strength and stiffness

Control PC

Ave

rage

Sub

base

Mod

ulus

, E

SB

-FW

D (

psi)

0

20000

40000

60000

80000July 2012 (shortly after stabilization)October 2012April 2013 (after spring-thaw)May 2013

Control PC

Ave

rage

Cal

iforn

ia b

earin

gra

tio in

sub

grad

e or

recy

cled

sub

base

, C

BR

SG

/RS

B

1

10

100

1000

10000July 2012 (shortly after stabilization)October 2012April 2013 (after spring-thaw)May 2013

Center for Earthworks Engineering Research 14

Fly ash stabilization (of subgrade) increases strength and stiffness

Con

trol

10%

FA

(Mus

catin

e)

10%

FA

(Por

t Nea

l)

15%

FA

(Am

es)

20%

FA

(Por

t Nea

l)

Ave

rage

Sub

base

Mod

ulus

, E

SB

-FW

D (

psi)

0

10000

20000

30000

40000

50000July 2012 (shortly after stabilization)October 2012April 2013 (after spring-thaw)May 2013

Con

trol

10%

FA

(Mus

catin

e)

10%

FA

(Por

t Nea

l)

15%

FA

(Am

es)

20%

FA

(Por

t Nea

l)

Ave

rage

Cal

iforn

ia b

earin

gra

tio in

sub

grad

e or

recy

cled

sub

base

, C

BR

SG

/RS

B

1

10

100

1000July 2012 (shortly after stabilization)October 2012April 2013 (after spring-thaw)May 2013

Time (minutes)

0 25 50 75 100 125 150 175 200

Res

ista

nce

(tsf

)

0

1

2

3

4

5

Ames FAMuscatine FAPort Neal FA

Initi

al S

et

Tim

e

Fin

al S

et T

ime

Set Times:Muscatine FA Initial = 107 min, Final = 170 minAmes FA Initial = 4 min, Final = 19 minPort Neal FA Initial = 3 min, Final = 6 min

Resistance at Final Set Time = 4.5 tsf

Center for Earthworks Engineering Research 15

Cement stabilized sections yielded comparatively higher modulus values overall from FWD testing

Con

trol

Mec

h. S

tab.

4 in

. Geo

cell

6 in

. Geo

cell

Non

-Wov

enW

oven

Bia

xial

Tria

xial

PC

(Sub

base

)P

C +

FP

Fib

erP

C +

MP

Fib

erR

ec. S

ubba

seP

C (S

ubgr

ade)

10%

FA

(Mus

catin

e)

10%

FA

(Por

t Nea

l)15

% F

A (A

mes

)

20%

FA

(Por

t Nea

l)

Ave

rage

Sub

base

Mod

ulus

, E

SB

-FW

D (

psi)

0

20000

40000

60000

80000July 2012 (shortly after stabilization)October 2012April 2013 (after spring-thaw)May 2013

Center for Earthworks Engineering Research 16

Cement stabilized sections yielded comparatively higher modulus values overall from DCP testing

Con

trol

Mec

h. S

tab.

4 in

. Geo

cell

6 in

. Geo

cell

Non

-Wov

en

Wov

en

Bia

xial

Tria

xial

PC

(Sub

base

)P

C +

FP

Fib

erP

C +

MP

Fib

erR

ec. S

ubba

seP

C (S

ubgr

ade)

10%

FA

(Mus

catin

e)10

% F

A (P

ort N

eal)

15%

FA

(Am

es)

20%

FA

(Por

t Nea

l)

Ave

rage

Cal

iforn

ia b

earin

gra

tio in

sub

grad

e or

recy

cled

sub

base

, C

BR

SG

/RS

B

1

10

100

1000October 2012April 2013 (after spring-thaw)May 2013

Ave

rage

Cal

iforn

iabe

arin

g ra

tio in

mod

ified

subb

ase,

CB

RM

SB

1

10

100

1000October 2012April 2013 (after spring-thaw)May 2013

ModifiedSubbase Layer

Subgrade orRecycledSubbase Layer

Center for Earthworks Engineering Research 17

Investments in foundation stabilization will increase modulus and can potentially lead to better pavement performance

0 2 4 6 8 10 12 14

Ave

rage

600

0 lb

Loa

ding

Dro

pF

WD

Ela

stic

Mod

ulus

, EF

WD

-6k (

psi)

[Ave

rage

of 9

to 3

0 te

sts]

0

20000

40000

60000

80000

4 in. Geocell

6 in. Geocell

Woven Geotextile

Nonwoven Geotextile

BX Polymer Grid

TX Polymer Grid

5% PC + 0.4% Fiberb (Subbase)

5% PC (Subbase)

10% PC (subgrade)

10% FA (Subgrade)

15% FA (Subgrade)

20% FA (Subgrade)

Average Material + Installation Cost ($/yd2)

0 2 4 6 8 10 12 14

Ave

rage

600

0 lb

Loa

ding

Dro

pF

WD

Ela

stic

Mod

ulus

, EF

WD

-6k (

psi)

[Ave

rage

of 9

to 3

0 te

sts]

0

20000

40000

60000

80000

4 in. Geocell

6 in. Geocell

Woven Geotextile

Nonwoven Geotextile

BX Polymer Grid

TX Polymer Grid

5% PC + 0.4% Fiberb (Subbase)

5% PC (Subbase)

10% PC (subgrade)

10% FA (Subgrade)

15% FA (Subgrade)

20% FA (Subgrade)

Control

(a)

(b)

Control

Note:a

Combined average for 5% PC + 0.4% FP fiber (subbase) and 5% PC + 0.4% MP fiber test sections

Note:a

Combined average for 5% PC + 0.4% FP fiber (subbase) and 5% PC + 0.4% MP fiber test sections

0 2 4 6 8 10 12 14

Ave

rage

600

0 lb

Loa

ding

Dro

p

FW

D E

last

ic M

odul

us,

EF

WD

-6k

(psi

)

[Ave

rage

of

9 to

30

test

s]

0

20000

40000

60000

80000

4 in. Geocell

6 in. Geocell

Woven Geotextile

Nonwoven Geotextile

BX Polymer Grid

TX Polymer Grid

5% PC + 0.4% Fiberb (Subbase)

5% PC (Subbase)

10% PC (subgrade)

10% FA (Subgrade)

15% FA (Subgrade)

20% FA (Subgrade)

Average Material + Installation Cost ($/yd2)

0 2 4 6 8 10 12 14

Ave

rage

600

0 lb

Loa

ding

Dro

p

FW

D E

last

ic M

odul

us,

EF

WD

-6k

(psi

)

[Ave

rage

of

9 to

30

test

s]

0

20000

40000

60000

80000

4 in. Geocell

6 in. Geocell

Woven Geotextile

Nonwoven Geotextile

BX Polymer Grid

TX Polymer Grid

5% PC + 0.4% Fiberb (Subbase)

5% PC (Subbase)

10% PC (subgrade)

10% FA (Subgrade)

15% FA (Subgrade)

20% FA (Subgrade)

Control

(a)

(b)

Control

Note:a

Combined average for 5% PC + 0.4% FP fiber (subbase) and 5% PC + 0.4% MP fiber test sections

Note:a

Combined average for 5% PC + 0.4% FP fiber (subbase) and 5% PC + 0.4% MP fiber test sections

0 2 4 6 8 10 12 14A

vera

ge 6

000

lb L

oadi

ng D

rop

FW

D E

last

ic M

odul

us, E

FW

D-6

k (

psi)

[Ave

rage

of 9

to 3

0 te

sts]

0

20000

40000

60000

80000

4 in. Geocell

6 in. Geocell

Woven Geotextile

Nonwoven Geotextile

BX Polymer Grid

TX Polymer Grid

5% PC + 0.4% Fiberb (Subbase)

5% PC (Subbase)

10% PC (subgrade)

10% FA (Subgrade)

15% FA (Subgrade)

20% FA (Subgrade)

Average Material + Installation Cost ($/yd2)

0 2 4 6 8 10 12 14

Ave

rage

600

0 lb

Loa

ding

Dro

pF

WD

Ela

stic

Mod

ulus

, EF

WD

-6k (

psi)

[Ave

rage

of 9

to 3

0 te

sts]

0

20000

40000

60000

80000

4 in. Geocell

6 in. Geocell

Woven Geotextile

Nonwoven Geotextile

BX Polymer Grid

TX Polymer Grid

5% PC + 0.4% Fiberb (Subbase)

5% PC (Subbase)

10% PC (subgrade)

10% FA (Subgrade)

15% FA (Subgrade)

20% FA (Subgrade)

Control

(a)

(b)

Control

Note:a

Combined average for 5% PC + 0.4% FP fiber (subbase) and 5% PC + 0.4% MP fiber test sections

Note:a

Combined average for 5% PC + 0.4% FP fiber (subbase) and 5% PC + 0.4% MP fiber test sections

Control PC

Ave

rage

Sub

base

Mod

ulus

, E

SB

-FW

D (

psi)

0

20000

40000

60000

80000July 2012 (shortly after stabilization)October 2012April 2013 (after spring-thaw)May 2013

0 2 4 6 8 10 12 14

Ave

rage

600

0 lb

Loa

ding

Dro

pFW

D E

last

ic M

odul

us, E

FW

D-6

k (

psi)

[Ave

rage

of 9

to 3

0 te

sts]

0

20000

40000

60000

80000

4 in. Geocell

6 in. Geocell

Woven Geotextile

Nonwoven Geotextile

BX Polymer Grid

TX Polymer Grid

5% PC + 0.4% Fiberb (Subbase)

5% PC (Subbase)

10% PC (subgrade)

10% FA (Subgrade)

15% FA (Subgrade)

20% FA (Subgrade)

Average Material + Installation Cost ($/yd2)

0 2 4 6 8 10 12 14

Ave

rage

600

0 lb

Loa

ding

Dro

pFW

D E

last

ic M

odul

us, E

FW

D-6

k (

psi)

[Ave

rage

of 9

to 3

0 te

sts]

0

20000

40000

60000

80000

4 in. Geocell

6 in. Geocell

Woven Geotextile

Nonwoven Geotextile

BX Polymer Grid

TX Polymer Grid

5% PC + 0.4% Fiberb (Subbase)

5% PC (Subbase)

10% PC (subgrade)

10% FA (Subgrade)

15% FA (Subgrade)

20% FA (Subgrade)

Control

(a)

(b)

Control

Note:a

Combined average for 5% PC + 0.4% FP fiber (subbase) and 5% PC + 0.4% MP fiber test sections

Note:a

Combined average for 5% PC + 0.4% FP fiber (subbase) and 5% PC + 0.4% MP fiber test sections

0 2 4 6 8 10 12 14

Ave

rage

600

0 lb

Loa

ding

Dro

pFW

D E

last

ic M

odul

us, E

FW

D-6

k (

psi)

[Ave

rage

of 9

to 3

0 te

sts]

0

20000

40000

60000

80000

4 in. Geocell

6 in. Geocell

Woven Geotextile

Nonwoven Geotextile

BX Polymer Grid

TX Polymer Grid

5% PC + 0.4% Fiberb (Subbase)

5% PC (Subbase)

10% PC (subgrade)

10% FA (Subgrade)

15% FA (Subgrade)

20% FA (Subgrade)

Average Material + Installation Cost ($/yd2)

0 2 4 6 8 10 12 14

Ave

rage

600

0 lb

Loa

ding

Dro

pFW

D E

last

ic M

odul

us, E

FW

D-6

k (

psi)

[Ave

rage

of 9

to 3

0 te

sts]

0

20000

40000

60000

80000

4 in. Geocell

6 in. Geocell

Woven Geotextile

Nonwoven Geotextile

BX Polymer Grid

TX Polymer Grid

5% PC + 0.4% Fiberb (Subbase)

5% PC (Subbase)

10% PC (subgrade)

10% FA (Subgrade)

15% FA (Subgrade)

20% FA (Subgrade)

Control

(a)

(b)

Control

Note:a

Combined average for 5% PC + 0.4% FP fiber (subbase) and 5% PC + 0.4% MP fiber test sections

Note:a

Combined average for 5% PC + 0.4% FP fiber (subbase) and 5% PC + 0.4% MP fiber test sections

Center for Earthworks Engineering Research 18

Correlations were made between FWD modulus and DCP penetration index

Penetration Index of Crushed LimestoneSubbase Layer, PICLS (mm/blow)

0.1 1 10 100

Ave

rage

6,0

00 lb

Loa

ding

Dro

pF

WD

Ela

stic

Mod

ulus

, EF

WD

-6k

(ps

i)1000

10000

100000

1000000October 2-3, 2012April 3, 2013

EFWD-6k = 47043 PI-0.9559

r2 = 0.6519

Penetration Index of Crushed LimestoneSubbase Layer, PICLS (mm/blow)

0.1 1 10 100

Ave

rage

14,

000

lb L

oadi

ng D

rop

FW

D E

last

ic M

odul

us, E

FW

D-1

4k (

psi)

100

1000

10000

100000

1000000 October 2-3, 2012April 3, 2013EFWD-14k = 39746 PI-1.0488

r2 = 0.6068

Penetration Index of ReclaimedSubbase, PIRSB (6 in. to 12 in.) or

Subgrade, PISG (6 in. to 12 in.) (mm/blow)

0.1 1 10 100

Ave

rage

6,0

00 lb

Loa

ding

Dro

pF

WD

Ela

stic

Mod

ulus

, EF

WD

-6k

(ps

i)

1000

10000

100000

October 2-3, 2012April 3, 2013October Best FitApril Best Fit

EFWD-6k(Oct) = 52241PI-0.3904

r2 = 0.2330

EFWD-6k(Apr) = 17801PI-0.4277

r2 = 0.5612

Penetration Index of ReclaimedSubbase, PIRSB (6 in. to 12 in.) or

Subgrade, PISG (6 in. to 12 in.) (mm/blow)

0.1 1 10 100

Ave

rage

14,

000

lb L

oadi

ng D

rop

FW

D E

last

ic M

odul

us, E

FW

D-1

4k (

psi)

1000

10000

100000

October 2-3, 2012April 3, 2013October Best FitApril Best Fit

EFWD-14k(Oct) = 41453PI-0.3385

r2 = 0.2058

EFWD-14k(Apr) = 17006PI-0.4431

r2 = 0.5438

(a)

(b)

(c)

(d)

Control PC

Ave

rage

Sub

base

Mod

ulus

, E

SB

-FW

D (

psi)

0

20000

40000

60000

80000July 2012 (shortly after stabilization)October 2012April 2013 (after spring-thaw)May 2013

Control PC

Ave

rage

Sub

base

Mod

ulus

, E

SB

-FW

D (

psi)

0

20000

40000

60000

80000July 2012 (shortly after stabilization)October 2012April 2013 (after spring-thaw)May 2013

Modified Subbase Layer Subgrade or Recycled Subbase Layer

Center for Earthworks Engineering Research 19

Multivariate statistical analyses showed that the surface subbase elastic modulus layer becomes statistically insignificant during the spring thaw

Term Estimate Standard Error t Ratio Prob. > t Statistically

Significant R2 Adj.

October 2012 Testinglog(EFWD) = b0 + b1∙log(PICLS) + b2∙log(PISG or RSB)

bo 10.469031 0.112847 92.77 <0.0001 Yes0.520b1 -0.561766 0.144323 -3.89 0.0002 Yes

b2 -0.194888 0.054533 -3.57 0.0007 YesApril 2013 (Spring Thaw) Testinglog(EFWD) = b0 + b1∙log(PICLS) + b2∙log(PISG or RSB)

bo 9.2933905 0.243899 38.10 <0.0001 Yes0.69b1 0.215623 0.128841 1.67 0.0991 No

b2 -0.546244 0.046481 -11.75 <0.0001 Yes

Center for Earthworks Engineering Research 20

A summary of key findings are as follows:

• During spring thawing, each test section experienced approximately 2 to 9 times reduction in FWD modulus or CBR

• Cement stabilized sections perform comparatively better than all other test sections, according to FWD and CBR measurements

• Investments in pavement foundation stabilization techniques can potentially result in better pavement performance, even during spring thawing

• Elastic modulus of surface granular layers become statistically insignificant to overall modulus during spring thaw

Center for Earthworks Engineering Research 21

Performance of the stabilized foundations will be monitored in the near and distant future

• Sections were paved with, PCC, HMA, and WMA this summer

• Long term performance study• Laboratory studies (In progress)

Center for Earthworks Engineering Research 22

Acknowledgments

The presenters would like to thank…• The Iowa Department of Transportation

• Mark Dunn, P.E.• Jesus Rodriguez

• Center for Earthworks Engineering Research (CEER) students• Lance Keltner• Nick Buse• Jinhui Hu• Yang Zhang

Thank You for your attention!