The Process of Making Composite Plastic Roads

A city’s plastic waste is put through three tasks – cleaning, drying and shredding. The plastic waste can include anything from sweet wrappers to shopping bags.

Once all the plastic waste is shredded (a technique where all the dust particles are eliminated, and plastic items are shredded into fine pieces) these are heated at 165°c. Next, the shredded pieces are added to bitumen mix, which is also heated at 160°c. The final mix is used for constructing roads.

The inventor of the process, Vasudevan melts shredded plastic over low heat to avoid emissions (Dr Vasudevan was honoured with one of India’s highest civilian awards, the Padma Shri, for his groundbreaking research on re-using waste plastic). Polystyrene is toxic when burned but, when softened, it makes an excellent pothole filler.

“Depending on the quality of tar, a 10-30 per cent of it is replaced with the waste plastic. Since both, tar and plastic are petroleum products they gel well together,” said Asad Warsi, Swachh Bharat Mission Consultant, Indore Municipal Corporation.

Every kilometer of a plastic tar road uses the equivalent of 1 million plastic bags, saving around one tonne of asphalt and costing roughly 8% less than a conventional road. 

In experiments to find uses for discarded plastic, Dr. Vasudevan found that in a molten condition, plastic had the property of an excellent binder. Acting on the principle that like attracts like, Dr Vasudevan looked at another chemical of similar nature: bitumen, a black tarry substance that was being combined with gravel to lay roads.

“Bitumen, a highly heterogeneous mixture of hydrocarbons is in effect, composed of polymers similar to plastic,” he says. When molten plastic was added to stone and bitumen mix, Dr Vasudevan found that, true to its nature, plastic stuck fast and bound both materials together.

The bitumen-modified plastic improved the tensile strength of the road by making it more durable and flexible. Plastic also prevented pothole formation. When the layer of molten plastic filled the space between the gravel and bitumen it thwarted rain water from seeping in and causing structural defects.

When late Dr Abdul Kalam, India’s former president and scientist visited Thiagarajar College, he encouraged Dr Vasudevan to lay the first plastic paved road within the campus. In 2002, he paved a 60-ft road within the campus with plastic-modified bitumen. The road is still intact in 2018.

In 2013, The Indian Road Congress developed Guidelines for the use of waste plastic in hot bituminous mixes (dry process) in wearing courses.

The guidelines state that studies have revealed that waste plastics have great potential for use in bituminous construction as its addition in small doses, about 5-10%, by weight of bitumen helps in substantially improving the Marshall stability, strength, fatigue life and other desirable properties of bituminous mix, leading to improved longevity and pavement performance. The use of waste plastic thus contributes to construction of green roads.

Only plastic conforming to Low Density Polyethylene (LDPE), High Density Polyethylene (HDPE), PET and Polyurethane shall only be used in pavement construction.