Use Of Plastic Waste In Rural Road Construction
Prof. Satish Chandra, Director
Dr. Sangita, Senior Principal Scientist, CSIR-CRRI, New Delhi
Plastic being a cheap material, is used in many applications and it has now become part of our everyday life style. Steady use of plastics has led to the increase in the amount of plastic waste being generated in India. These wastes as part of municipal waste are randomly dumped on the outskirts of a city, occupying vast land areas, which otherwise can be used for other purposes of welfare of society.
This discarded waste plastic is consumed by animals and birds resulting in their death. Flood-like situations are often created in metropolitan cities due to clogging of drainage with plastic wastes. It also leads to ground water pollution and global warming. It is estimated that more than 15,000-tonne of plastic waste is generated in India, out of which 9,000 ton is collected and processed, whereas, remaining plastic waste is not collected. Disposal of plastic waste materials through land filling or incineration is not effective as it further pollutes the environment by generating toxic gases and due to chances of fire at landfill site.
Prof. Satish ChandraProcess of Utilization
There are three different possible processes to incorporate waste plastic into bituminous mixes. Dry Process: In this process, the waste plastic is added to hot aggregates to get Plastic Coated Aggregates (PCA). Optimum quantity of bitumen is then added to produce waste plastic modified bitumen mix WPMB-MIX. A 1-3mm particle size of waste plastic in shredded or powder form is preferable for commercial production of mix and field trials have successfully been completed in India in several Metro cities including Bengaluru, Chennai, Kerala, Tamilnadu and Delhi since 2002.
Wet Process: Waste Plastic along with other additive is melted and stirred in hot bitumen at around 150°C using a high shear mixer to produce WPMB, which is then added to hot aggregates to produce Modified Bituminous Mix. The process has been patented by Central Road Research Institute, Delhi but the process is yet to be commercialized. Field trials are also required to validate the process.
Semi Wet Process: Waste plastic is miscible in bituminous phase in hot melt condition and gets separated from bituminous phase on cooling. But, some of the plastics in the mixed waste stream do not melt completely and remains dispersed despite adding additives as during recycling process plastics are toughened with colourant dyes and other fillers, chemical and inert additives. Partially Modified Bitumen containing undisclosed waste plastic particles is then used to coat the hot aggregates to produce Waste Plastic Modified Bituminous Mixes. The undisclosed plastic acts as a cushion aggregate in modified mixes at ambient temperature to service temperature. This process is preferred over wet process to have the dual benefit of plastic waste i.e. as a modifier to bitumen and as a cushion for better interlocking of aggregates. This process is also under validation. The total quantity of waste plastic used in all the three applications is 8-12 per cent by weight of bitumen.
Based on the laboratory studies and field performance inputs from various researchers, National Rural Roads Development Agency (NRRDA), Ministry of Rural Development, Government of India, has formulated guidelines for the use of plastic waste in rural roads construction. The guidelines say that the performance studies carried out on the roads (using waste plastic) constructed in Tamil Nadu indicated “satisfactory performance with good skid resistance, good texture value, stronger and less amount of progressive unevenness over a period”. The experiments conducted at CRRI also indicated better performance of the mix containing waste plastic. The guidelines recommend the use of poly films with thickness up to 60 micron, hard and soft foams and laminated polymer with thickness of up to 60 microns. However, poly vinyl chloride sheets (flex sheets) are not for their use in bituminous mixes. The process of coating aggregate with molten (waste) plastic does not require any machinery and no toxic gases evolve in the process. It is recommended that the percentage of shredded waste plastic will be 8% for blending the bitumen in the construction of plastic roads.
Dr. SangitaIndian Roads Congress has also published “Guidelines for the Use of Waste Plastic in Hot Bituminous Mixes (Dry Process) in Wearing Courses”, vide IRC SP-98 2013, which clearly indicate the use of plastic waste in dense and open graded mixes. Type of waste plastic and its source, advantages, limitations and design of mixes of using waste plastic in road construction are covered in these guidelines. Open graded mixes like premixing surfacing and mixed seal are still in practice in rural roads.
Senior Principal Scientist
Advantages of Plastic Roads
A well-constructed Plastic Tar Road will result in the following advantages as given in the NRRDA guidelines for use of waste plastic in road construction.
- Strength of the road increased (Increased Marshall Stability Value)
- Better resistance to water and water stagnation
- No stripping and have no potholes.
- Increased binding and better bonding of the mix.
- Increased load withstanding property (Withstanding increased load transport)
- Overall consumption of bitumen decreases.
- Reduction in pores in aggregate and hence less rutting and ravelling.
- Better soundness property.
- Maintenance cost of the road is almost nil.
- The Road life period is substantially increased.
- No leaching of plastics.
- No effect of radiation like Ultra violet (UV) rays.
The process is easy to execute. All the plastic gets collected and sent to a place where it is shredded into fine pieces, making it convenient to use. The pieces are then mixed into a mixture of bituminous concrete or tar. Both the elements are heated at high temperature before mixing. Contrary to popular belief, using plastic is cheaper too. Therefore, if the plastic waste is properly channelized in road development across the country, the civic bodies can make roads, which are cheaper and durable.
Applications in Field
In 2015, the Indian government made it mandatory to incorporate plastic waste in the construction of roads. More than 1,600-tonne of plastic has been used to lay over 1,000-km of roads in Tamil Nadu in the last five years as part of the government’s thrust on effective use of plastic waste. Maharashtra state authorities have already tied up with one agency for building twelve trial plastic roads across the city of Pune. The city of Indore is already recycling half of its plastic waste on daily basis, where 30% is being used in roads. So far, more than 500 km of roads have been constructed. Two kilometres of bituminous concrete
overlay were laid on Road No.43 in Delhi in 2007 also and later on several other roads like Sarita Vihar T-Point to Okhla Barrage, Kalka Temple to ESI Hospital road, Sachivalaya Road, etc. A 25-km road with waste plastic was laid in Bangalore. The plastic road performed better than conventional road laid at the same time, which began developing “crocodile cracks” after few months of its laying (Fig. 4). In 2007-08, bituminous concrete overlay containing waste plastic was laid on 3.6 km length of road in Delhi under the supervision of CRRI. Jamshedpur is the only city in eastern India where an environmentfriendly technology with incorporation of waste plastic into bituminous mix (Dry Process) has been implemented using accumulated waste plastic of the city (Fig. 5). Jamshedpur Utility and Services Company (JUSCO) has constructed 12-15 km roads in the steel city, as well as widened 22 roads by way of using waste plastic, including biscuit packets, poly bags, etc. It has been reported that for every one-km long and four-metre-wide road one ton of bitumen will be saved if this technology is adopted.
The use of recycled waste plastic in pavement asphalt represents a valuable outlet for such materials. The use of modified bitumen with the addition of processed waste plastic of about 5-10% by weight of bitumen helps in substantially improving the strength, fatigue life and other desirable properties of bituminous concrete mixes. It also reduces the consumption of bitumen. Plastic coating on aggregates provides better binding with bitumen due to increased bonding and increased area of contact between polymers and bitumen. The polymer coating also reduces the voids. This prevents the moisture absorption and oxidation of bitumen by entrapped air. The roads can withstand heavy traffic and show better durability as there is reduction in water absorption. The process is easy to execute and does not require any modification to the plant. The plastic roads made from recycled materials are not only greener but are also stronger and economical. It is an earnest step to reduce the plastic waste. Using it to lay roads is the most viable solution.
Civil Engineering & Construction Review is a leading monthly news journal, launched in 1988, at New Delhi, India by Trend-Set Engineers Pvt. Ltd. Its dedication to reader satisfaction and also towards fulfilling the ever - growing needs of the construction profession, makes CE&CR the first choice of all those connected with the construction industry.