WHITE TOPPING : LONG LASTING CONCRETE OVERLAY OF BITUMINOUS PAVEMENTS

1. WHITE TOPPING : LONG LASTING CONCRETE OVERLAY OF BITUMINOUS PAVEMENTS BINOD KUMAR SCIENTIST RIGID PAVEMENTS DIVISION CENTRAL ROAD RESEARCH INSTITUTE

2. White Topping is defined as a Portland Cement Concrete (PCC) overlay constructed on the top of the existing distressed bituminous pavement White Topping is a PCC resurfacing (overlay) as a rehabilitation or structural strengthening alternative on bituminous pavement

3. Advantages of White Topping • Long life, low maintenance, low life cycle cost, improved safety and environmental benefits • Bituminous overlay exhibits a more rapid loss of serviceability as compared to concrete white topping • Deformation like rutting and cracking predominant in case of bituminous pavement which is normally absent with concrete surfaces of white topping

4. Conventional White Topping improves structural capacity of existing bituminous pavement, if built on strong base course, and it impedes structural distresses. • White Topping exhibits better reflectance, reduction in heat island effect (Albedo), reduction in street light requirements. • White Topping is quite cost effective to tackle annual budget constraints and high traffic levels

5. TYPES OF WHITETOPPING • Conventional White Topping (200mm or more) • Thin White Topping (TWT) (100-200mm) • Ultra-Thin White Topping (UTWT)(≤ 100 mm)

6. Conventional White Topping (CWT) • A PCC overlay of thickness 200mm or more designed and constructed without consideration of any bond between the concrete overlay and underlying bituminous layer • It is constructed as a new rigid pavement without assuming any composite action • CWT treats the existing bituminous surface as a subbase • Bituminous surface should not suffer from any isolated damages like subsidence or material related problems

7. Thin White Topping (TWT) • PCC overlay thickness greater than 100 and less than 200 is known as Thin White Topping(TWT) • The bond between the overlaid PCC and underlying bituminous layer is often a consideration but not mandatory • High strength concrete with fibres are commonly used • Joint spacing – 0.6 to 1.25m

8. CONVENTIONAL WHITE TOPPING/ THIN WHITE TOPPING • Localized areas of weakness can be strengthened through patching. Milling can remove a number of asphalt surfaces distresses.

9. TWT Overlays Application More Heavy Loaded Routes • Rural Roads • Medium to Moderately Heavy Volume Roads(e.g MDR, SH, Low Traffic NH) • Intersections • Minor Airports Pavements

10. Ultra Thin White topping • PCC overlay Thickness equal to less than 100 mm is known as Ultra Thin White Topping(UTWT) • Bonding is mandatory in between the underlying bituminous layer and overlaid PCC layer. • Bonding is achieved by milling the existing bituminous surface upto 25mm depth. • Joint Spacing – 0.6 to 1.25 m

11. ULTRA THIN WHITE TOPPING(UTWT)

12. UTWT OVERLAY APPLICATIONS Light Loaded Routes • Low Volume Roads (Urban Streets, village roads) • Parking lots • Footpaths • Residential Streets • Intersection

13. Location where UTWT/TWT Constructed in India

14. COMPOSITE BENDING ACTION OF UTWT AND TWT

15. MIX DESIGN • Typical higher cement content • Fast track type construction • Low water/cement ratio • Steel fibers/Synthetic • Creates Durable concrete, quick to opening to traffic.

16. CONSTRUCTION STEPS FOR UTWT/TWT

17. CONSTRUCTION STEPS • Mill and clean surface. • Place concrete, finish and cure • Early sawing is required • Opening to traffic.

18. MILLING • Milling can remove significant surface distortions that likely contain poor quality asphalt material • Milling is used to reduce high spots and help ensure desired overlay depth and reduce the quantity of concrete needed to fill low spots • Milling roughens the surface to enhance the bond between the new concrete overlay and the asphalt • Direct placement without milling is recommended when rutting in the existing asphalt pavement does not exceed 2”. • Any ruts in the existing pavement are filled with concrete, resulting in a thicker concrete overlay above the ruts

19. CLEANING OF SURFACE • Air Blasting/vacuum cleaner • Power Brooming • Water Blasting • Sand Blasting

20. MILLING IN PROGRESS MILLED & CLEANED SURFACE

21. SCRAPING IN PROGRESS CLEANING OF SCRAPED SURFACE

22. PAVING WITH VIBRATING SCREED PAVING WITH SLIPFORM PAVER

23. FINISHING & TEXTURING CURING COMPUND SPRAY

24. JOINT SAWING SAWING DEPTH H/3 TO H/4

25. COST COMPARISON BITUMEN OVERLAY Vs. WHITE TOPPING (Cost of 1 km Road 7 m wide) Note: In case of white topping, the cost is taken if concrete is purchased from RMC plant. If contractor has his own batching plant, a saving of Rs. 50 per sq meter can be achieved

26. REFERENCES • IRC: SP:76-2008 Tentative Guidelines For Coventional, Thin And Ultra-thin Whitetopping • NCHRP Synthesis 338, “ Thin and Ultrathin Whitetopping” • NCHRP Synthesis 204, “ Portland Cement concrete Resurfacing” • American Concrete Pavement Association publications • Guide to Concrete overlay solutions (National Concrete Pavement Technology Centre

27. THANK YOU