The increased interest in white topping has been noticed, chiefly, in Thin and Ultra-Thin White Topping during the last decade. Their effectiveness has further augmented interest in them because; they satisfy the demand caused by rapidly deteriorating highways confronted with limited fund availability.
The concepts of “Sustainability” and “Sustainable development” are of much importance and receiving much attention from all walks of life as the causes of global warming and climate changes are debated world over. Concrete White topping Technology is sustainable because of its long life (over 30 years).
One of the promising materials that will be used for Road rehabilitation is Ultra-Thin White Topping (UTWT). White Topping is defined as an overlay of Portland Cement Concrete (PCC) constructed on the upper surface of a present bituminous pavement. White Topping is thus PCC resurfacing (overlay) as a restoration or physical solidification alternative on Asphalt or Bituminous pavement.
UTWT overlays are designed on the principle of a composite pavement structure which distributes traffic and environmental loading in a different manner than done in case of conventional PCC or flexible pavement. In case of such bonded system due to the composite action between concrete and flexible layer, the neutral axis shifts downward with the result that much of the area of PCC slab comes under compression and therefore a lesser thickness is required to carry the load than in the case with conventional PCC layer.
The other factor in case of UTWT and TWT is that spacing of joints is considerably reduced due to which both curling ad warping stresses are much less. Although a fully bonded system is ideal, the same, however, is very difficult to be realised and usually a partial bond is realised.
The Greater Hyderabad Municipal Corporation (GHMC) is probably the first corporation in India to use white topping technology for road construction. White topping is a new technology of providing cement concrete overlay on the existing damaged and distressed bitumen roads with a purpose either to restore or to increase the load carrying capacity, or both. The newly-inducted technology by GHMC also works on the existing pavement and prevents frequent damage of roads.
GHMC has adopted this technology for two pilot projects – Road No 10 in Banjara Hills and PG Road in Secunderabad. After successful implementation of laying these roads stretches, the Government of Telangana and GHMC have formulated a proposal to carry this work over bitumen roads in several stretches in the premises. Accordingly, as many as 64 road stretches have been identified for the deployment of white topping overlay over bitumen roads in a phased manner.
According to GHMC official, white topping roads have a design life of 15-20 years. Roads designed with white topping do not require maintenance for 15 years. Meanwhile, white topping roads along with provisions of footpath, shoulders, stormwater drain with proper chamber correction and all other utilities duct are sustainable. These have long life, low-maintenance, low life cycle cost, with improved safety and environment benefits.
White topping was being used widely in the US, Europe, and some countries in Asia. The white topping layer keeps the road intact during rains, as it prevents water-logging. This technology uses fly ash and polymeric fibre, besides cement and sand, which strengthens the road surface. White topping is the covering of an existing asphalt pavement with a layer of Portland cement concrete. White topping is divided into types depending on the thickness of the concrete layer and whether the layer is bonded to the asphalt substrate.
The technique is very simple to understand and practice. The initial cost of the investment for UTWT is comparative to conventional bituminous pavement is quite high but the overall Budget of the Project is comparatively less.