WHITE TOPPING : LONG LASTING CONCRETE OVERLAY OF BITUMINOUS PAVEMENTS BINOD KUMAR SCIENTIST RIGID PAVEMENTS DIVISION CENTRAL ROAD RESEARCH INSTITUTE 1
Jan 04, 2016
WHITE TOPPING : LONG LASTING CONCRETE OVERLAY OF BITUMINOUS PAVEMENTS
BINOD KUMAR
SCIENTISTRIGID PAVEMENTS DIVISION
CENTRAL ROAD RESEARCH INSTITUTE
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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
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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
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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
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•Localized areas of weakness can be strengthened through patching. Milling can remove a number of asphalt surfaces distresses.
CONVENTIONAL WHITE TOPPING/ THIN WHITE TOPPING
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TWT Overlays Application
Rural RoadsMedium to Moderately
Heavy Volume Roads(e.g MDR, SH, Low Traffic NH)
IntersectionsMinor Airports
Pavements
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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
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ULTRA THIN WHITE TOPPING(UTWT)
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Low Volume Roads (Urban Streets, village roads)
Parking lots
Footpaths
Residential Streets
Intersection
Light Loaded Routes
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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
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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
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CONSTRUCTION STEPS
Mill and clean surface.Place concrete, finish and cureEarly sawing is requiredOpening to traffic.
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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
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CLEANING OF SURFACE
Air Blasting/vacuum cleaner
Power Brooming
Water Blasting
Sand Blasting
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MILLING IN PROGRESS
MILLED & CLEANED SURFACE
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SCRAPING IN PROGRESS
CLEANING OF SCRAPED SURFACE
PAVING WITH SLIPFORM PAVER
PAVING WITH VIBRATING SCREED
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FINISHING & TEXTURING
CURING COMPUND SPRAY
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JOINT SAWING
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SAWING DEPTH H/3 TO H/4
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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
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