REHABILITATION OPTIONS.. GROUP 3.pptx.pptx

Pavement rehabilitation

1. REHABILITATION OPTIONS GROUP THREE

2. General.

3. General… The purpose of pavement rehabilitation is commonly related to inadequate service levels for the road users in combination with excessive costs in maintaining the existing pavement structure.

4. Design period..

5. General cont.… The following options are availability for pavement rehabilitation: Overlays with a new surfacing and base course The flexible base overlay has been used as an intermediate layer of a new structure, placed directly on top of an old structure. The primary purpose, in addition to adding additional structure, has been to resist the propagation of reflective cracks from the old structure.

6. General cont.… Overlays with a new surfacing Resurfacing of a road pavement or other paved area is undertaken for one or more of the following reasons: • to add strength to the construction to prolong its life; • to correct the surface profile and thus improve riding quality and surface water drainage; • to restore skid-resistance to an old surfacing polished by traffic; • to restore the aesthetic appearance of a worn, aged surface.

7. General cont.… Partial reconstruction by reworking the existing pavement and adding new pavement layers as required Full reconstruction by downgrading of the existing pavement to sub grade for the new pavement.

8. General cont.… Which method is the appropriate for a road section depends on the following: Condition of the existing pavement. Strength requirements for the new pavement. Types of material in the existing pavement. Available materials for construction of the new pavement. Required surface levels of the new road Construction practicalities.

9. Overlays

10. Overlays cont.… Applicability Overlays are used for the following purposes: To add sufficient structural strength so the pavement can carry the future traffic in the design period. To restore the riding the quality of the pavement.

11. Overlays cont.… Overlays shall not be used under the following conditions: Where there is uncertainty about the performance of the overlay due to defects in the existing base course or in patches in the existing pavement on pavement with deformation (shoving) in bituminous layers unless repair or removal of the deformed material on severely cracked pavements where there is risk of early crack reflection through the new layers.

12. Overlays cont…. Shoving: Is a permanent displacement of the asphalt surface typically cause by traffic loading. When traffic pushes against the pavement surface, it produces a short , abrupt wave in the pavement surface. This can occur at intersection or entrance/ exit ramps on freeways when breaking can occur suddenly and with a lot of force.

13. Overlays cont…. Shoving distresses occur due to insufficient stability in the asphalt mixture as compared to the tire pressure placed on the pavement in the given scenario.

14. Shoving

15. Overlays cont... Reflective cracking.. Cracks in a flexible overlay over an existing crack or joint. The cracks occur directly over the underlying cracks of joints. ‘Joint reflection cracking’ specifically refers to reflection cracks arising from underlying pavement joint movement. Reflection cracks can occur over existing pavement cracks, cement or lime stabilized base,etc.

16. Overlays cont.…. Possible causes : Differential movement across the underlying crack of joint. For joint reflection cracking, this is movement of the PCC slab beneath the HMA surface because of thermal and moisture changes. Generally not load initiated, however loading can hasten deterioration.

17. Reflective cracking

18. Overlays cont… Materials The materials types selected for overlays shall meet the requirements given in design catalogue Chapter 8- Pavement design-New Roads and in Chapter 7 – Pavement materials. The material coefficients for pavement and sub grade materials are given in the following table:-

19. Overlays… Overlay design When an overlay is placed, restoring of the drainage system shall always be included. The general requirement for layer thickness is that d max shall not exceed 2/3 0f he compacted layer thickness.. The table below gives alternative overlay designs for varying degrees of required strengthening..

20. Overlays cont…. All selection of surfacing type and base course material type shall meet the requirements for the respective traffic load class given in Table 8.4 to 8.8 in chapter 8 – Pavement Design –New roads.

21. Overlays cont… Overlays with granular base course The table 9.9 in Pavement and material DESIGN manual-1999 provides an option to use graded crushed rock as base course (CRR) in overlays. This option shall be used with discretion and particular attention to the following: the underlying surface must be freely drained, particularly where depressions or ruts are present, in order to avoid water being trapped in the new base course layer the layer thickness given in table 9.9 shall not be compromised by unevenness in the existing surface, consideration shall be given to reprocessing of the existing pavement ( partial reconstruction) if the existing surface is deformed.

22. Types of Overlay The overlay combination are divided into Four categories based on Type of existing pavement and the overlay: Flexible overlay over flexible pavement Flexible overlay over rigid pavement Rigid overlay over rigid pavement Rigid pavement over flexible pavement The choice of overlay type depends upon number of factors including thickness of overlay required , local materials, wheel load costs .

23. Flexible overlay over flexible pavement Steps in Design of Overlays: Measurement and estimation of the strength of the existing pavement. Design life of overlaid pavement. Estimation of the traffic to be carried by the overlaid pavement. Determination of the thickness.

24. Flexible Pavement failure Fatigue (Alligator) Cracking Decrease in pavement load supporting characteristics . Loss of base, sub base or sub grade support (e.g., poor drainage) Increase in loading (e.g., more or heavier loads than anticipated in design) 2. Bleeding Bleeding occurs when asphalt binder fills the aggregate voids during hot weather and then expands onto the pavement surface . 3. Depression Frost heave or sub grade settlement resulting from inadequate compaction during construction. 4. Potholes potholes are the end result of alligator cracking. As alligator cracking becomes severe, the interconnected cracks create small chunks of pavement, which can be dislodged as vehicles drive over them .

25. Pavement Conditions Cracking Bleeding Depression

26. Pavement Conditions

27. Overlay

28. Overlay is that reinforcing layer that we provide over an existing pavement. Structural overlays make the layers of pavement thicker, adding structural support to the pavement. In addition to structural benefits, there are performance increases associated with a structural overlay, such as additional smoothness, better aesthetics, and an extended service life. The objective is to provide a minimum thickness of overlaying material that will reduce the unit stress on the next lower layer, commensurate with the load-carrying capacity of the material comprising that layer. If the existing pavements have completely deteriorated, an overlay would not serve the purpose and the solution would be to remove the existing damage pavement structure and to rebuild the same. In partially damage pavement sections, patch repair works are carried out before constructing the overlay.

29. Effective Thickness Method Basic concept Thickness of overlay is the difference between the thickness required for a new pavement and the effective thickness of the existing pavement : h OL = h n –h e Where, h OL = thickness of overlay h n = thickness of new pavement h e = effective thickness of existing pavement

30. All thicknesses of new and existing materials must be converted into an equivalent thickness of AC where, h i = thickness of layer C i = conversion factor for layer

31. Example Thickness of existing pavement 250 mm GSB 250 mm WBM 100 mm BM 40 mm AC Thickness of new pavement 300 mm GSB 250 mm WMM 100 mm DBM 40 mm AC

32. Example Condition of old pavement layers GSB and WBM layers are in good condition with PI of fines more than 6 Conversion factor = 0.1 BM layer shows aggregate degradation Conversion factor = 0.5 AC layer shows appreciable cracking Conversion factor = 0.6 Effective thickness of the old pavement: h e = 0.1×(250+250) + 0.5×100 + 0.6×40= 124 mm

33. Example Equivalent thickness of new pavement in terms of AC h n = (300+250)×0.2 + (100+40)×1.0 = 250 mm Thickness of Overlay = h n – h e = 250 – 124 = 126 mm

34. table 9.9 in Pavement and material DESIGN manual-1999

35. Partial reconstruction.

36. Partial reconstruction cont.... General.. Partial reconstruction is reprocessing or removal of material from the existing pavement to let the existing pavement form either base course or sub base in the new pavement. Whether the existing pavement forms a new base course or new sub base depend on: The material properties of the existing pavement layers The condition of the existing pavement The strength requirements for the new pavement Any required adjustments of road levels. Table 8.4 to 8.8 in chapter 8 – Pavement Design –New roads in Pavement and Materials Design Manual-1999 shall be used for the selection of pavement layers.

37. Partial Construction cont…. Reprocessing the old pavement to base course in the new Pavement.. The base course, consisting of the reprocessed old pavement, shall fulfill the requirements for base course in accordance with the design catalogue Reprocessing the old pavement to sub base in the new pavement The sub base, consisting of the reprocessed old pavement, shall fulfill the requirements for sub base in accordance with the design catalogue.

38. Full reconstruction.

39. Full Construction cont…. Existing pavement is reprocessed to improved subgrade in the new Pavement.. The pavement design – New Roads shall be used for selection of surfacing , base course and sub base. Table 8.4 to 8.8 will guide the surfacing;….. Also the subgrade of the old pavement should meet the requirement for subgrade according to Chapter 5…