WHITE TOPPING : LONG LASTING CONCRETE OVERLAY OF BITUMINOUS PAVEMENTS

BINOD KUMAR

SCIENTISTRIGID PAVEMENTS DIVISION

CENTRAL ROAD RESEARCH INSTITUTE

1

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 2

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 3

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

4

5

1)Conventional White Topping (200mm or more)

2)Thin White Topping (TWT) (100-200mm)

3)Ultra-Thin White Topping (UTWT)(≤ 100 mm)

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

6

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

7

•Localized areas of weakness can be strengthened through patching. Milling can remove a number of asphalt surfaces distresses.

CONVENTIONAL WHITE TOPPING/ THIN WHITE TOPPING

8

TWT Overlays Application

Rural RoadsMedium to Moderately

Heavy Volume Roads(e.g MDR, SH, Low Traffic NH)

IntersectionsMinor Airports

Pavements

9

More Heavy Loaded Routes

Ultra Thin White toppingPCC 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

10

ULTRA THIN WHITE TOPPING(UTWT)

11

12

Low Volume Roads (Urban Streets, village roads)

Parking lots

Footpaths

Residential Streets

Intersection

Light Loaded Routes

13

Location where UTWT/TWT Constructed in IndiaSr.

NoLocation, Year &

ThicknessApp. Length and

subbaseMaterials, Grade of Concrete

1 In Front of Pune Municipal Corporation, 2003, 125mm

20 m over asphalt pavement

FRCM40

2 CRRI Campus road,2004, 40-75mmNew Delhi

300m over asphalt, DLC and Concrete pavement

FRC,HPC,HPFRC M 35

3 MoolChand and PremBari Underpass , 2006, 125 mm, New Delhi

500m over reinforced concrete slab

FRC, M40 using portland slag cement

4 HRDC Centre, Ghaziabad, 2006, 50 mm

1.75 km over M 7.5 DLC laid over asphalt pavement

HPFRC, M35

5 NDMC Office Campus road at parliament street,2006,100 mm

200m over asphalt pavement

FRC, M35

6 Hosur Road, Bangalore, 2011, 150 mm

Over sceapped bituminous pavement

M45

7 Mahul Road, Mumbai,100mm,2006-07

30-50m over milled asphalt surface

HPFRC, M50

14

15

Typical higher cement content

Fast track type construction

Low water/cement ratio

Steel fibers/Synthetic

Creates Durable concrete, quick to opening to traffic.

CONSTRUCTION STEPS FOR UTWT/TWT

16

CONSTRUCTION STEPS

Mill and clean surface.Place concrete, finish and cureEarly sawing is requiredOpening to traffic.

17

MILLINGoMilling can remove significant surface distortions that likely contain poor quality asphalt material

oMilling is used to reduce high spots and help ensure desired overlay depth and reduce the quantity of concrete needed to fill low spots

oMilling roughens the surface to enhance the bond between the new concrete overlay and the asphalt

oDirect placement without milling is recommended when rutting in the existing asphalt pavement does not exceed 2”.

oAny ruts in the existing pavement are filled with concrete, resulting in a thicker concrete overlay above the ruts

18

CLEANING OF SURFACE

Air Blasting/vacuum cleaner

Power Brooming

Water Blasting

Sand Blasting

19

20

MILLING IN PROGRESS

MILLED & CLEANED SURFACE

21

SCRAPING IN PROGRESS

CLEANING OF SCRAPED SURFACE

PAVING WITH SLIPFORM PAVER

PAVING WITH VIBRATING SCREED

22

FINISHING & TEXTURING

CURING COMPUND SPRAY

23

JOINT SAWING

24

SAWING DEPTH H/3 TO H/4

25

COST COMPARISON BITUMEN OVERLAY Vs. WHITE TOPPING

(Cost of 1 km Road 7 m wide)

No

TYPE OF PAVEMENT

DESIGN REFERENCE

SPECIFICATION TOTAL COST(Lakhs)

COST per sq. m

1. Bitumen overlay

IRC-37 DBM 65mmBC 50mm

Rs.62.1 Rs. 890

2 White Toppings

IRC-76 Milling / ScrappingProfile correction 40 mmConcrete 150 mm-M 45 (RMC Laying with paver machine and groove cutting with diamond blade machine)

Rs. 79.53 Rs. 1150

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

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 26

27