Bitumen is a useful binder for road construction and elastomers like natural rubber, crumb rubber, SBR, etc. as well as plastomeric substances like Polyethylene, Ethylene Vinyl Acetate and Ethylene Butyl Acrylates are mixed with bitumen to modify its properties to give better quality. By adding small amounts of polymers to bitumen, the life span of the road pavement may be considerably increased.
Thinner polythene/polypropylene carry bags are the most abundantly disposed of wastes, which may not be collected by ragpickers for onward recycling because of lower returns. These polythene/polypropylene bags are easily compatible with bitumen at specified conditions and a blend can be prepared and used for road laying.
Almost 90% of the polymeric materials are made up of either polyethylene or polypropylene or polystyrene, which being heated at around 130-1400c gets softened without releasing any gaseous products, while, when PVC is incinerated (>7000c), it may produce toxic gases like Dioxins.
Homopolymers, like high and low density polyethylene and polypropylene, as well as random and block copolymers, like ethylene-vinyl acetate, ethylene/propylene, styrene-b-butadiene-b-styrene and styrene-b-ethyl-ene-co butylene-b-styrene, have been used as bitumen modifiers. Polymer blended bitumen has better properties regarding softening point, penetration point, ductility, stripping value and marshall stability value. Hence the blend can be used for laying flexible pavement.
In the process of the preparation of polymer-bitumen aggregate mix, the temperature used is only-1700C and no chlorine or copper is present in the system. The polymer materials used are polyethylene, polypropylene and polystyrene only and polyvinyl chloride is not used to avoid the possibility of presence of chlorine in the system because of which Dioxin does not form.
The whole process is very simple and economical and needs no new machinery.
The technology is also very simple and the waste plastics available in the surrounding area can be used then and there.
Crumb rubber requires a temperature of 1800C whereas 60/70 grade bitumen needs 1600C only. This accounts for fuel conservation.
Roads have been laid at different places at Tamil Nadu using different surface area and different composition are performing well.
A scheme for laying waste plastics-Tar road in rural area for 1000 km was launched on 16th July, 2003 at Namakkal by the Honourable Chief Minister of Tamil Nadu Dr. J. Jayalalitha.