Crack-Opening and Crack-Spacing in Cement Treated Base Layers

CROW Infradagen 2014

Woldekidan M.F., Huurman M.

Presenter: R. Huurman

Bound Base layers : Semi-rigid Pavements

- Offer some advantages of Rigid Pavements

• distribute higher loads better minimize subgrade loads

•When succesull, offers good durability & high performance

- Attractive from environmental aspect (eg use of recycled

materials)

Disadvantage:

- Cracking is envitable

- When cracks grow to surface performance is

compromised

Background

CTB advantages are maintained only if cracking is controlled

Prediction tools are of paramount importance

Background

What initiates cracking?

Factors:

• Temperature loads

• Cement hydration (shrinkage)

• Traffic loads

• Pavement boundary conditions

• etc

Approach

Concept: crack initiation mechanism

Approach

• Fixed ends with infinite length

• Shrinkage in CTB (Hydration+Temperature fluctuation)

• Restrained interfaces

DT

Tensile stresses develop at the center

Crack initiation to crack growth

Approach

• Crack initiationcrack tip

• Fracture mechanics:

- analysis of crack tip to full crack formation

Scope : crack initiation moment

Material strength & stress state sxx

Approach

All factors direct-indirect dictate the ultimate stress sxx in the CTB

Material strength sxx dictate moment of crack initiation

H

Establish relationship between sxx and the various influencing factors !

- 2D FE Modeling

Finite Element Modeling

- Temprature loads are appliedDevelopment of sxx is analyzed

Variables:

•Geometry: Thickness (H) and Length (L)

•Boundary condition (Bedding constant, Ch)

•Material Properties ( aT, E-modulus )

H

Simulation sxx , Uxx

Finite Element Modeling

Data Analysis

FEM Results

- Higher bedding constant higher sxx , lower Uxx

- Higher E higher sxx, higher Uxx for intermidiate values of Ch

H

0

0.1

0.2

0.3

0.4

1.E-06 1.E-04 1.E-02 1.E+00

σxx

Ch [MPa/mm]

H=250 mmL=30mΔT=5°C

7 GPa

5 GPa

10 GPa

-0.6

-0.5

-0.4

-0.3

-0.2

-0.1

0

1.E-06 1.E-04 1.E-02 1.E+00U

xxCh [MPa/mm]

H=250 mmL=30mΔT=5°C

7GPa

5GPa

10GPa

Data Analysis

FEM Results

- Higher bedding constant higher sxx and lower Uxx

-Higher L higher sxx for intermidiate values of Ch

- Higher L higher Uxx for low to intermed.values of Ch

H

-0.6

-0.5

-0.4

-0.3

-0.2

-0.1

0

1.E-06 1.E-04 1.E-02 1.E+00

Uxx

Ch [MPa/mm]

H=250 mmL=30mΔT=5°C

7GPa

5GPa

10GPa

-0.6

-0.5

-0.4

-0.3

-0.2

-0.1

0.0

1.E-06 1.E-04 1.E-02 1.E+00

Uxx

Ch [MPa/mm]

H=250 mmE=7GPaΔT=5°C

10m

20m

30m

0

0.1

0.2

0.3

0.4

1.E-06 1.E-04 1.E-02 1.E+00

σxx

Ch [MPa/mm]

H=250 mmL=30mΔT=5°C

7 GPa

5 GPa

10 GPa

0

0.1

0.2

0.3

0.4

1.E-06 1.E-04 1.E-02 1.E+00

σxx

Ch [MPa/mm]

H=250 mmE=7GPaΔT=5°C

10m

20m

30m

Regression analysis

FEM Results

Sxx .maxss

Sxx .maxss )])/(exp(1[ nrS

])].[)/)1((exp([ 111max SbaRSCUU m

xx

0

0.1

0.2

0.3

0.4

1.E-06 1.E-04 1.E-02 1.E+00

σxx

Ch [MPa/mm]

H=250 mmE=7GPaΔT=5°C

10m

20m

30m

-0.6

-0.5

-0.4

-0.3

-0.2

-0.1

0

1.E-06 1.E-04 1.E-02 1.E+00

Uxx

Ch [MPa/mm]

H=250 mmL=30mΔT=5°C

7GPa

5GPa

10GPa

Model Accuracy: Description of the FE simulated data

FEM Results

0

0.05

0.1

0.15

0.2

0.25

0.3

0.35

0.4

0 10 20 30 40 50

σxx

[M

Pa]

Length [m]

FE data0.50.010.0050.0010.00050.00010.000050.000005

-0.6

-0.5

-0.4

-0.3

-0.2

-0.1

0

0 10 20 30 40 50

Uxx

[mm

]

Length [m]

FE data0.50.010.0050.0010.00050.00010.000050.000005

Loads: Temperature and Traffic

Time Varying factors

-20.00

-15.00

-10.00

-5.00

0.00

5.00

10.00

15.00

20.00

25.00

30.00

0 2 4 6 8 10 12

Tem

pe

ratu

re

Years

1985

0.00

0.10

0.20

0.30

0.40

0.50

0.60

0 2 4 6 8 10 12

Years

traf

fic

stre

ss [

MP

a]

Material Properties: E-modulus, fc, ft, ec

Time Varying factors

0

2000

4000

6000

8000

10000

12000

14000

0 2 4 6 8 10 12

Emo

du

lus

[ M

Pa]

Years

0

5

10

15

20

25

30

0 2 4 6 8 10 12

Dru

kste

rkte

[ M

Pa]

Years

0

0.5

1

1.5

2

2.5

0 2 4 6 8 10 12

Tre

kste

rkte

[ M

Pa]

Years

-5.E-04

-4.E-04

-3.E-04

-2.E-04

-1.E-04

0.E+00

0 2 4 6 8 10 12

Uit

dro

gin

gskr

imp

[ -

]

Years

Tool Outputs

Interface jaar 1985

doorlopend 1

eerste dag 150

lineaire temp coefficient 1.06E-05 [-/°C] 7 tot 10 E-6

Horizontale beddingconstante 0.00100 [Mpa/mm] tussen 0.01 en 0.001??? Zoek dit uit!

Dikt 250.00 [mm]

a b 28 dgn

druksterkte 0.417651 0.5 2.21

Eo 900 dit is 1800 bij beton

eps sc inf -4.00E-04 dit is 1 tot 7E-04 voor beton

sig traffic 0.004587 0.5

open 28

precracklength 0 <=25 m; uncracked = 0

0.0

1.0

2.0

3.0

4.0

5.0

6.0

7.0

8.0

0

5

10

15

20

25

30

35

40

0 2 4 6 8 10

Cra

ck o

pe

nin

g [m

m]

Cra

ck s

pac

ing

[ m

]

Years

Crack spacing

Crack opening

Tool Outputs

Crack spacing & Opening

0.0

1.0

2.0

3.0

4.0

5.0

6.0

7.0

0

5

10

15

20

25

30

35

40

0 2 4 6 8 10

Cra

ck o

pe

nin

g [m

m]

Cra

ck s

pac

ing

[ m

]

Years

Crack spacing

Crack opening

Precrack@5m

0.0

1.0

2.0

3.0

4.0

5.0

6.0

7.0

8.0

0

5

10

15

20

25

30

35

40

0 2 4 6 8 10

Cra

ck o

pe

nin

g [m

m]

Cra

ck s

pac

ing

[ m

]

Years

Crack spacing

Crack opening

Tool Outputs

Crack spacing & Opening

Lower Embedconst. 0.0

2.0

4.0

6.0

8.0

10.0

12.0

0

5

10

15

20

25

30

35

40

0 2 4 6 8 10

Cra

ck o

pe

nin

g [m

m]

Cra

ck s

pac

ing

[ m

]

Years

Crack spacing

Crack opening

0.0

1.0

2.0

3.0

4.0

5.0

6.0

7.0

8.0

0

5

10

15

20

25

30

35

40

0 2 4 6 8 10

Cra

ck o

pe

nin

g [m

m]

Cra

ck s

pac

ing

[ m

]

Years

Crack spacing

Crack opening

Tool Outputs

Crack spacing & Opening

2X strain-Krimp 0.0

1.0

2.0

3.0

4.0

5.0

6.0

7.0

8.0

9.0

0

5

10

15

20

25

30

35

40

0 2 4 6 8 10

Cra

ck o

pe

nin

g [m

m]

Cra

ck s

pac

ing

[ m

]

Years

Crack spacing

Crack opening

Tool Outputs

Crack spacing & Opening

0.0

1.0

2.0

3.0

4.0

5.0

6.0

7.0

8.0

9.0

0

5

10

15

20

25

30

35

40

0 2 4 6 8 10

Cra

ck o

pe

nin

g [m

m]

Cra

ck s

pac

ing

[ m

]

Years

Crack spacing

Crack opening

Practical tool for predicting performance

Suitable for incorporating expected variations in Material

properties

Useful for optimization (performance vs Material

selection/pavement geometry)

Future improvements:

Traffic stress estimates can be improved: relations can be

developed using Multi-layer analyses.

Conclusions

Questions?

Thank you

For your attention