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Sunday , 24 March 2024

Whitetopping : Durable And Cost Effective Concrete Overlay

ULTRA THIN WHITETOPPING

Thin Whitetopping at PuneUTWT typically involves placing 50mm to 100mm thick concrete overlay with joint spacing ranging from 1.0m to 1.5m. It is mainly used for the areas with very low volume of light traffic like two wheelers and cars as is normally observed on internal colony lanes. Bonding between underlying bituminous layer and overlaid PCC layer is mandatory in case of UTWT. Milling the existing bituminous surface to an average depth of 25mm is normally used to provide the bonding at the interface between the existing bituminous surface and PCC overlay. Milling not only removes the top deteriorated part of the bituminous layer but it also produces a rough surface which can develop some kind of bonding between the existing milled bituminous surface and concrete overlay. The bonding helps ultra thin concrete overlay to sustain traffic for a longer period.

THIN WHITETOPPING

Milling on Existing Bituminous Surface WhitetoppingTWT concrete overlay is 100mm to 200mm thick with the same joint spacing of 1.0m to 1.5m. The bond between the overlaid PCC and underlying bituminous layer is often a consideration but it is not mandatory. The bonding consideration may be ignored in the design.

CONVENTIONAL WHITETOPPING

Conventional whitetopping is more than 200mm thick with the joint spacing and slab size (3.5m x 4.5m) similar to concrete pavement. It is designed and constructed without consideration of any bond between the concrete overlay and underlying bituminous layer. Conventional whitetopping is designed and constructed like a new rigid pavement without assuming any composite action. Conventional whitetopping treats the existing bituminous surface as a sub-base like Dry Lean Concrete (DLC) and to this extent the condition of existing bituminous surface does not matter significantly, except that bituminous surface should not suffer from any isolated damages like subsidence or material related problems.

CASE STUDIES

In the recent past many projects of whitetopping have been completed on city and colony roads either with milling or even without milling.

Pune

Pune city has adopted TWT treatment for internal roads as well as wider roads with higher traffic volume. Started in 2008, Pune city has constructed above 75 to 80km of roads (approx. 9 lakh sqm) with TWT technology. The roads constructed in 2008 are in excellent condition and this technology shall effectively save a huge recurring maintenance cost to the city for the next 20 to 25 years. Pune city has used TWT technology (125mm concrete overlay) for past six years and now the roads with heavy traffic are also being done using this technology (175mm concrete overlay). The cost of whitetopping has been around `950/m2.

Bangalore

View of CompletedPeripheral road in Bangalore city is of 4.0km in length. It has 4-lane divided carriageway with 11.4m wide paved width on either sides (7.2m carriageway + 1.2m paved shoulder on inner edge + 3.0m paved shoulder on outer edge). This road has been provided with 180mm thick thin whitetopping. The existing asphalt surface was milled to depth of 20-40mm. The milled surface was cleaned by both manual and mechanical means (compressed air and sand blasting). Paving of concrete was performed by Slip form Paver capable of paving 8m width in one go. Panel size was kept 1m x 1m.

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