1. Crack-Opening and Crack-Spacing in Cement
Treated Base Layers
CROW Infradagen 2014
Woldekidan M.F., Huurman M.
Presenter: R. Huurman

2.  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

3.  CTB advantages are maintained only if cracking is controlled
Prediction tools are of paramount importance
Background

4.  What initiates cracking?
Factors:
• Temperature loads
• Cement hydration (shrinkage)
• Traffic loads
• Pavement boundary conditions
• etc
Approach

5. 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

6. Crack initiation to crack growth
Approach
• Crack initiationcrack tip
• Fracture mechanics:
- analysis of crack tip to full crack formation
Scope : crack initiation moment

7. 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 !

8. - 2D FE Modeling
Finite Element Modeling
- Temprature loads are appliedDevelopment of sxx is analyzed
Variables:
•Geometry: Thickness (H) and Length (L)
•Boundary condition (Bedding constant, Ch)
•Material Properties ( aT, E-modulus )
H

9. Simulation sxx , Uxx
Finite Element Modeling

10. 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 mm
L=30m
ΔT=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+00Uxx
Ch [MPa/mm]
H=250 mm
L=30m
ΔT=5°C
7GPa
5GPa
10GPa

11. 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 mm
L=30m
ΔT=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 mm
E=7GPa
ΔT=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 mm
L=30m
ΔT=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 mm
E=7GPa
ΔT=5°C
10m
20m
30m

12. Regression analysis
FEM Results
Sxx .maxss 
Sxx .maxss  )])/(exp(1[ n
rS 
])].[)/)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 mm
E=7GPa
ΔT=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 mm
L=30m
ΔT=5°C
7GPa
5GPa
10GPa

13. 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[MPa]
Length [m]
FEdata
0.5
0.01
0.005
0.001
0.0005
0.0001
0.00005
0.000005
-0.6
-0.5
-0.4
-0.3
-0.2
-0.1
0
0 10 20 30 40 50
Uxx[mm]
Length [m]
FEdata
0.5
0.01
0.005
0.001
0.0005
0.0001
0.00005
0.000005

14. 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
Temperature
Years
1985
0.00
0.10
0.20
0.30
0.40
0.50
0.60
0 2 4 6 8 10 12
Years
trafficstress[MPa]

15. 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
Emodulus[MPa]
Years
0
5
10
15
20
25
30
0 2 4 6 8 10 12
Druksterkte[MPa]
Years
0
0.5
1
1.5
2
2.5
0 2 4 6 8 10 12
Treksterkte[MPa]
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
Uitdrogingskrimp[-]
Years

16. 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

17. 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
Crackopening[mm]
Crackspacing[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
Crackopening[mm]
Crackspacing[m]
Years
Crack spacing
Crack opening
Precrack@5m

18. 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
Crackopening[mm]
Crackspacing[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
Crackopening[mm]
Crackspacing[m]
Years
Crack spacing
Crack opening

19. 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
Crackopening[mm]
Crackspacing[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
Crackopening[mm]
Crackspacing[m]
Years
Crack spacing
Crack opening

20. 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
Crackopening[mm]
Crackspacing[m]
Years
Crack spacing
Crack opening

21.  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

22. Questions?
Thank you
For your attention