Finite element modelling of Ultra-Thin Continuously Reinforced Concrete Pavement

1. Finite element modelling of Ultra-Thin Continuously Reinforced Concrete Pavement Phia Smit - PhD Candidate (University of Pretoria) 8 July 2019

2. What is Ultra-Thin Continuously Reinforced Concrete Pavement? • 50 mm concrete surfacing • High Strength Steel Fibre Reinforced Concrete • Steel bar mesh • 50 x 50 mm mesh • 5.7 mm diameter

3. What is Ultra-Thin Continuously Reinforced Concrete Pavement? • Why develop UTCRCP?

4. Background • Perspective on difference in thickness • Should we consider UTCRCP as a flexible pavement? • Differential, vertical permanent deformation (rutting)? Concrete layer Concrete layer Conventional concrete pavement Substructure Substructure UTCRCP 300 mm 50 mm Brown & Selig (1991) Brown & Selig (1991)

5. Purpose of research Investigate the response of UTCRCP to traffic loading (by making use of 3D FEA): • Effect of load configuration on road pavements with thin asphalt or thin concrete bound layers • Effect of relative stiffness by varying concrete bound layer thickness and base E-value • Effect of layer interaction by varying concrete bound layer – base interaction properties • Effect of boundary conditions in terms of model depth

6. 3D FEA model setup FEA model from literature: • Kim (2007) • FEA of flexible pavements considering nonlinear behaviour of substructure Model to replicate • Domain size determined to have no boundary effects

7. 3D FEA model setup – single wheel loading • Quarter symmetry • Boundary conditions • Interaction • Load application: 550 kPa, radius = 152.4 mm • Elements: C3D20R

8. 3D FEA model setup – axle loading

9. Effect of load configuration on road pavement with thin asphalt or thin concrete bound layers Wheel centreline Load location Wheel centreline Load location Axle centreline

10. Effect of load configuration on road pavement with thin asphalt or thin concrete bound layers Parameters • Critical parameters as per Kim (2007) • Deflection plots (transverse) • Contour plots of displacement in substructure

11. Critical parameters *Single Wheel loading – SW Difference (%) = (SWvalue – Axlevalue)/(Swvalue)*100 **Axle loading - Axle

12. Critical parameters *Single Wheel loading – SW Difference (%) = (SWvalue – Axlevalue)/(Swvalue)*100 **Axle loading - Axle

13. Critical parameters *Single Wheel loading – SW Difference (%) = (SWvalue – Axlevalue)/(Swvalue)*100 **Axle loading - Axle

14. Deflection plot Centreline of wheel Centreline of axle *Single Wheel loading - SW **Axle loading - Axle

15. Deflection plot - normalized Centreline of wheel Centreline of axle *Single Wheel loading - SW **Axle loading - Axle

16. Deflection plot - normalized Centreline of axle Centreline of wheel *Single Wheel loading - SW **Axle loading - Axle

17. Concrete bound layer model - vertical displacement contours Centreline of wheel Centreline of wheel Centreline of axle Base Subgrade Vertical displacement (mm) Vertical displacement (mm) Single wheel Axle

18. Concrete bound layer model - horizontal displacement contours Centreline of wheel Centreline of wheel Centreline of axle Base Subgrade Horizontal displacement (mm) Single wheel Axle

19. Effect of relative stiffness by varying concrete bound layer thickness and base E-value • Response surface methodology • Central composite design Y: E-value Second-order surface plot Critical parameter = A+ B*X + C*Y - D*X2+ E*Y2 - F*X*Y X: Thickness

20. Effect of relative stiffness by varying concrete bound layer thickness and base E-value • Parameters: • Response surface plots of critical parameters as per Kim (2007) • Deflection plots (transverse)

21. Surface plots of critical parameters δvertical (mm) σbottom BL (kPa) • σtop subgrade (kPa)

22. Deflection plot Centreline of wheel Centreline of axle

23. Effect of layer interaction by varying concrete bound layer – base interaction properties • Interaction properties • Normal behaviour: • Allowed to detach • Tangential behaviour: • Assigned friction coefficient • Frictionless, 0.1, 0.35 and 0.6 • Parameters: • Critical parameters as per Kim (2007)

24. Effect of layer interaction by varying concrete bound layer – base interaction properties

25. Effect of boundary conditions in terms of model depth • Concrete layer: • 76 mm to 50 mm

26. Effect of boundary conditions in terms of model depth • Concrete layer: • 76 mm to 50 mm • Reduced depth: • Subgrade - • 20.955 m to 3.657 m

27. Effect of boundary conditions in terms of model depth

28. Conclusions • Reducing the depth had little effect on the critical parameters, but resulted in upward movement of the model free-end at the right • Allowing the concrete layer to detach from its supporting layer influences critical parameters more than varying the friction coefficient between the layers • Both road pavements with thin asphalt and thin concrete layers would benefit from being modelled with complex load configurations

29. Conclusions • Axle loading results in a hogging moment along the axle centreline • Axle loading influences the vertical and horizontal displacement in the substructure • Concrete layer thickness has a dominant effect on critical parameters • As the thickness is reduced, the deflected shape changes

30. Recommendations • The stress and strain induced in the substructure of UTCRCP should be further investigated (using LE) • UTCRCP should be modelled incorporating more complex material models for the substructure: • Stress dependency • Low tensile strength • Permanent deformation • Result in significant stress-redistribution and more accurate understanding of the response of UTCRCP to loading

31. Sponsor

32. Thank you