In Situ Stabilization of Pavement Base Courses

1. In Situ Stabilization of Pavement Base Courses Roads Pavement Forum Thursday, May 17, 2001

2. Introduction • Clients • Gautrans • C&CI • SANRAL • Laboratory and Heavy Vehicle Simulator results from R243/1 • One building block in a long-term process • Focus on mechanical properties and structural bearing capacity

3. Layout of presentation • Purpose of the study • Materials • Experimental plan • Results for each laboratory test • Conclusions

4. Purpose • Assess the benefits of in situ stabilization in terms of improvements in the mechanical properties and structural bearing capacity of the treated material • Mechanical properties • Resilient modulus • Compressive and tensile strength • Flexibility • Shear strength • Bearing capacity • Effective fatigue • Permanent deformation

5. Materials • Basic material • Ferricrete milled from HVS test site, including existing surfacing and upper portion of subbase • Treatment processes • Cement (Laboratory) • 2 % cement • Foam and cement (Laboratory and HVS) • 2 % cement, 1.8 % residual binder • Emulsion and cement (Laboratory and HVS) • 2 % cement, 1.8 % residual binder

6. Materials: Untreated • Nominal maximum aggregate size 37.5 mm

7. Materials: Untreated • Classification • Grading G4 • Atterberg limits G5 • CBR G7

8. UCS, ITS, Flexural Beam Test • Treated materials only • Foam and emulsion tested at 2 binder contents • 1.8% residual binder content + 2% cement • 3.0% residual binder content + 2% cement

9. Flexural beam test • Strain at crack initiation • Indication of flexibility

10. Triaxial Tests • Untreated and treated materials • 1.8% residual binder content, 2 % cement • Variables • Density • Saturation • Confining pressure • Stress ratio

11. Triaxial tests • Static triaxial tests • Shear strength parameters • Dynamic triaxial tests • Resilient modulus • Permanent deformation response

12. Compressive strength:UCS Results • Cement-treated ferricrete has highest UCS • Addition of binder reduces the UCS

13. Tensile strength:ITS Results • Cement-treated ferricrete has highest ITS • Addition of binder reduces the ITS

14. Tensile strength:ITS Results • Samples dried to equilibrium MC at ambient temp • 72 h in oven at 40º C

15. Flexibility:Flexural beam test • Flexibility only increases at higher binder content

16. Elastic stiffness (Mr):Dynamic triaxial tests • Estimation of stiffness values • Use regression model for untreated ferricrete • Use ranges for treated materials

17. Comparative results:Average strain-at-break

18. Comparative results: Effective fatigue life • SAMDM transfer functions • Working strain of 125  • b–values from flexural beam test

19. Comparative results:Cohesion

20. Comparative results:Friction angle

21. Comparative results:Shear strength at 3 = 50 kPa

22. Comparative results:Bearing capacity (9 % PD)

23. HVS tests:Pavement structure • 30 mm Asphalt • 250 mm FTG / ETG - 1,8 % residual bitumen - 2 % cement • In situ material • In situ subgrade

24. Foam-treated Emulsion-treated HVS tests:Materials

25. HVS tests:Programme • 2 x 100 m long experimental sections • Foam-treated • Emulsion-treated • 1st Phase of HVS testing • 80/100 kN tests (350 000/150 000 repetitions) • Completed • 2nd Phase of HVS testing • 40 kN tests (750 00000 repetitions) • In process

26. HVS tests:Deflection result

27. Conclusions:UCS, ITS and Flexibility • Complex relationship between UCS, ITS and • Percentage binder • Cementation • Curing procedure • Flexibility • No increase in flexibility at low binder content • Increase in flexibility and effective fatigue life at higher binder content • Strain-at-break slightly higher for foam-treatment at higher binder content • Effective fatigue life models to be validated with HVS results

28. Conclusions:Resilient modulus • Increase in resilient modulus with treatment • Untreated ferricrete • Resilient modulus influenced by • Relative density and saturation • Stress state • Treated ferricrete • Resilient modulus dictated by the stabilizing agent and largely insensitive to the above parameters • No significant difference between stabilizing agents • Resilient modulus values to be validated by HVS back-calculation results

29. Conclusions:Shear strength and plastic strain • Shear strength increases with treatment • Vastly improved bearing capacity in terms of permanent deformation • Cement-treatment shows highest benefit • No significant difference between foam- and emulsion-treatment • Models need to be calibrated with HVS results

30. Conclusions:General • Only considered mechanical properties • Other properties to investigate • Permeability and erodibility • Workability • Shrinkage cracking • Time to opening the road – early strength • Improved understanding of mechanical properties and behaviour • Properties of stabilized material significantly different from untreated material even at low binder content • First structural design models for these types of materials