Plastic Roads: Use of Waste Plastic in Construction of Roads

ABSTRACT

The global plastic production is increasing rapidly with rise in population and changes in life style. This makes the disposal of plastic is becoming complicated because of the non-biodegradable property. So, it is better to recycle than disposal. One of the trends in recycling of plastic is use in construction of roads. This type of recycling can also help in protecting the environment from the greenhouse gases that are exposed to atmosphere while disposal. The waste plastic in form of bottles, cups, caps, etc are made in form of powder or blended with crusher and coated over the aggregate and bitumen mixture by heating process for roads construction. This polymer coated aggregate and bitumen mixture shows high strength, better binding property, stability, and increase in wear resistance, better durability and tear of roads. This makes the recycle of plastic in an efficient manner.

1.      INTRODUCTION

            Today every sector around the world from agriculture to electrical, packing, automobile, building construction, communication sectors are widely using plastic. The usage was started after the industrial revolution and its large-scale production seemed to be cheap. Plastic is light in weight, moisture resistant, flexible and very inexpensive. These qualities increase our propensity towards plastic and hence making its use very common. It has revolutionized all spheres of life. But this plastic ultimately becomes a waste. It is a common site both in urban and rural areas to see plastic wastes littering the roads. It forms the major portion of the total municipal solid wastes (MSW). Generally, plastic is a non-biodegradable and many research found that plastic take around 4500 years to degrade. Several studies proven that the disposal of plastic causes many health problems and also reduces the fertility of soil. The plastic production over the world has crossed 400 million tons and the recycling of plastic is only 10%. Its improper disposal can cause serious health hazards in humans.

Fig 1: Increase in consumption of plastic year by year

            It is estimated that approximately 10 thousand tons per day (TPD) of plastics waste is generated i.e., 9% of 1.20 lacs TPD of MSW in India. The plastic waste constitutes two major categories of plastics; (i) Thermoplastics and (ii) Thermoset plastics. Thermoplastics, constitutes 80% and thermoset constitutes approximately 20% of total post-consumer plastics waste generated in India. The Thermoplastics are recyclable plastics which include; Polyethylene Terephthalate (PET), Low Density Poly Ethylene (LDPE), Poly Vinyl Chloride (PVC), High Density Poly Ethylene (HDPE), Polypropylene (PP), Polystyrene (PS) etc. However, thermoset plastics contains alkyl, epoxy, ester, melamine formaldehyde, phenolic formaldehyde, silicon, urea formaldehyde, polyurethane, metalized and multilayer plastics etc. The use of plastic materials such as carry bags, cups, etc. is constantly increasing. Nearly 50 to 60% of the total plastics are consumed for packing.

Fig 2: Current scenario of waste plastic

            In order to contain this problem experiments have been carried out whether this waste plastic can be reused productively. Waste plastic such as carry bags, disposable cups and laminated pouches like chips, pan masala, aluminum foil and packaging material used for biscuits, chocolates, milk and grocery items can be used for surfacing roads.

2.      PLASTIC ROADS

            Dr. Rajagopalan Vasudevan is an Indian scientist working mainly in waste management. He developed an innovative method to reuse plastic waste to construct better, more durable and very cost-effective roads. Dr. Vasudevan, known as the ‘Plastic Man of India,’ has been praised by Prime Minister Narendra Modi and also awarded the Padma Shri in the Year 2018.  His method has been used to lay 5,000 kms of roads across 11 states using recycled plastic. Plastic waste can be used as coating over aggregate and this coated stone can be used for road construction. The main function of plastic is to be effectively utilized in construction of flexible pavement as a binder material for replacing the content of bitumen. By this process a road of 1 km length and 3.375m width of single lane can consumes 10,00,000 carry bags and the road strength is increased by 100% and there found no any pot hole. On other side, the road traffic is increasing. The load bearing capacities of the road are to be increased. So, need to take care of both these aspects. The use of this innovative technology will not only strengthen the road construction but also increase the road life as well as will help to improve the environment.

            The plastic wastes have been utilized in the construction of pavements in India since a decade now. The road constructed using waste plastic i.e., carry bags, bottles, cups and thermocoles is known as ‘Plastic Road’. They are found to be perform better compared to those constructed with conventional bitumen. Plastic used in road construction is not new. It is already in use as PVC or HDPE pipe mat crossings built by cabling together PVC (polyvinyl chloride) or HDPE (high-density poly-ethylene) pipes to form plastic mats. The plastic roads include transition mats to ease the passage of tyres up to and down from the crossing. Both options help protect wetland haul roads from rutting by distributing the load across the surface. But the use of plastic-waste has been a concern for scientists and engineers for a quite long time.

Fig 3: India’s first plastic road (Jamshedpur)

3.      SALIENT FEATURES OF THE POLYMER-WASTE-BITUMEN ROAD

            The Road strength of this road is twice stronger than normal roads; resistance towards water stagnation i.e., no potholes are formed; less bleeding during summer; burning of plastics waste could be avoided; it doesn’t involve any extra machinery; it doesn’t increase cost of road construction; and it helps to reduce the consumption of bituminous mix vis-à-vis reduce cost.

4.      CONCEPT OF UTILIZATION OF WASTE PLASTIC IN BITUMINOUS MIXES FOR CONSTRUCTION OF ROAD

   I.    Materials Used

          The materials used for carrying out the present research are:

Aggregates,

Bitumen,

Waste Plastic Modifiers

          The various laboratory tests were carried out on these materials and the results were computed.

Aggregate:

          Aggregates used in surface course can be divided into two types according to their size: coarse aggregates and fine aggregates. Coarse aggregates are generally defined as those retained on the 2.36 mm sieve. Fine aggregates are those that pass through the 2.36 mm sieve and are retained on the 0.075 mm sieve. Aggregates required for the research work will be procured from the local market. The properties of the aggregates are of considerable significance to the highway engineer. Some of the desired properties of these aggregates are strength, durability, toughness, hardness, etc.

Bitumen:

          Bitumen acts as binding agent for aggregates in bituminous mixes. Generally, in India bitumen used in road construction of flexible pavement is of grades 60/70 or 80/100 penetration grade. Both the grade of bitumen confirming to BIS standards will be used for the present studies. Bitumen may further be divided into petroleum asphalt or bitumen and native asphalt. There are different forms in which native asphalts are available. These are those which occur in a pure or nearly pure state in nature. The viscosity of bitumen is sometimes reduced by a volatile diluent; this material is called cutback. When bitumen is suspended in a finely divided condition in an aqueous medium and stabilized with an emulsifier, the material is known as emulsion.

Waste Plastic Modifiers:

          Modifiers are generally used to enhance the properties of bituminous concrete mixes by reducing the air void present between the aggregates and also to bind them together so that no bleeding of bitumen will occur. For the present study plastic waste such as carry bags, water bottles, milk packets, glasses, cups, etc will be used as a modifier.

II.    Processing Details

a.       Collection of waste plastic,

b.       Cleaning and shredding of waste plastic,

c.       Mixing of shredded waste plastic, aggregate and bitumen in central mixing plant.

a.      Collection of waste plastic:

            Waste plastic is collected from roads, garbage trucks, dumpsites or compost plants, or from school collection programs, or by purchase from rag-pickers or waste-buyers at Rs 5-6 per kg Rag-pickers.

Fig 4: Collection of plastic waste

b.     Cleaning and shredding of waste plastic

            Waste plastic litter in the form of thin-film carry-bags, use-and-throw cups, PET bottles, etc. these are sorted, de-dusted, washed if necessary. Fig. cleaning process Plastic waste which is cleaned is cut into a size between 1.18mm.

Fig 5: Shredded plastic waste being sprayed over hot aggregates

c.      Mixing of shredded waste plastic, aggregate and bitumen in central mixing plant

            The aggregate mix is heated to 165Ëšc (as per the HRS specification) in central mixing plant. Similarly, the bitumen is to be heated up to a maximum of 160Ëšc. The 8% of waste plastic to the weight of bitumen are added in the conveyor belt or special mechanical device is developed which will spray the plastics inside the chamber to coat the plastics effectively. Central mixing plant helps to have better control of temperature and better mixing of this material thus helping to have a uniform coating and heated bitumen is also sprayed. Fig. central mixing plant.

Fig 6: Bitumen being mixed with plastic coated aggregates

   III.    Laying of Bitumenous mix

a.       Mix Design by Marshall method

b.       Optimum waste plastic content

a.      Mix Design by Marshall method:

            Laboratory studies were carried out at the Centre for Transportation Engineering of Bangalore University on the possible use of the processed plastic bags as an additive in bituminous concrete mixes. The material used in this study was supplied by M/s KK Poly Flex (P) Ltd., Bangalore. The processed plastic was used as an additive with heated bitumen in different proportions (ranging from zero to 12 % by weight of bitumen) and mixed well by hand, to obtain the modified bitumen. The properties of the modified bitumen were compared with ordinary bitumen. It was observed that the penetration and ductility values of the modified bitumen decreased with the increase in proportion of the plastic additive, up to 12 % by weight. The softening point of the modified bitumen increased with the addition of plastic additive, up to 8.0 %by weight. Auto Marshall Compactor Auto Marshall tester 11.

b.     Optimum waste plastic content:

            Varying percentages of waste plastic by weight of bitumen was added into the heated aggregates Marshall specimen with varying waste plastic content was tested for bulk density and stability Maximum value of stability was considered as criteria for optimum waste plastic content Studies were carried out on Bituminous mixes using 60/70 grade bitumen having average Marshall Stability Value (MSV) of 1300 kg at optimum bitumen content of 5.0 % by weight of the mix. Further studies on mixes were carried out using the modified binder obtained by the addition of varying proportions of processed plastic bags (percentage by weight of bitumen) with the conventional 80 /100 grade bitumen. The optimum modified binder content fulfilling the Marshall Mix design criteria was found to be 5.0 % by weight of the mix, consisting of 8.0 % by weight of processed plastic added to the bitumen. The average MSV of the mix using the modified binder was found to be as high as 1750 kg at this optimum binder content, resulting in about three-fold increase in stability of the BC mix, which contains 4.6 % bitumen plus 8 % processed plastic by weight of bitumen, i.e.,0.4 % processed plastic by weight of the mix.

            In order to evaluate the ability of the mix prepared with the above-modified bitumen to withstand adverse soaking condition under water, Marshall Stability tests were conducted after soaking in water at 60 Co for 24 hours. The average MSV of the BC mix with modified binder (using 8 % processed plastic by weight of bitumen, as above) was found to increase by about 2.6 times of the mix with ordinary bitumen. Further laboratory studies carried out on the BC mixes using this modified binder also indicated note worthy increase in fatigue life under repeated application of loads.

Dry process is recommended for isolated works.

            It is recommended that the percentage of shredded waste plastic will be 8% by CRRI, while the same is specified as 10% by Dr. Vasudevan. However, we can adopt 8% as the optimum plastic content for blending the bitumen in the construction of plastic roads. The details of the process are given below. Bitumen of grades 60/70 or 80/100 can be used as binder as in case of conventional method.

With Mini Hot Mix Plant

            The stone aggregate mix (as per specification) is transferred to the mix cylinder where it is heated to 165Ëšc (as per the IRC specification) and then it is transferred to the mixing puddler (Temperature can be monitored using IR thermometer), while transferring the hot aggregate into the puddler, calculated quantity of shredded plastics is sprayed over the hot aggregate within 30seconds. The sprayed plastic films melt and gets coated over the aggregate, thus forming an oily coating. Similarly, the bitumen is to be heated to a maximum of 160Ëšc in a separate chamber and kept ready (The temperature should be monitored to have good binding and to prevent weak bonding). At the mixing puddler, the hot bitumen is added over the plastic-coated aggregate and the resulted mix is used for road construction. The road laying temperature is between 110Ëšc to 120Ëšc. The roller used is normal 8 ton capacity.

5.      COMPARISON OF PROPERTIES IN ORDINERY ROAD AND PLASTIC ROAD

            The durability of the roads laid out with shredded plastic waste is much more compared with roads with asphalt with the ordinary mix. Roads laid with plastic waste mix are found to be better than the conventional ones. The binding property of plastic makes the road last longer besides giving added strength to withstand more loads. While a normal 'highway quality' road lasts four to five years it is claimed that plastic-bitumen roads can last up to 10 years. Rainwater will not seep through because of the plastic in the tar. So, this technology will result in lesser road repairs. And as each km of road with an average width requires over two tons of polyblend, using plastic will help reduce non-biodegradable waste. The cost of plastic road construction may be slightly higher compared to the conventional method. However, this should not deter the adoption of the technology as the benefits are much higher than the cost. Plastic roads would be a boon for India’s hot and extremely humid climate, where temperatures frequently cross 50°C and torrential rains create havoc, leaving most of the roads with big potholes. Already, a kilometre long test-track has been tested in Karnataka using this technology. The government is keen on encouraging the setting up of small plants for mixing waste plastic and bitumen for road construction. It is hoped that in near future we will have strong, durable and eco-friendly roads which will relieve the earth from all type of plastic-waste.

Fig 7: Durability of Plastic Road

1.      Economy:

            One of the main factors to be considered in any technology and global market is economy. In order to compare the cost of construction between ordinary road and plastic-coated bituminous road, consider a road of dimensions 3.75m width and 1Km distance.

Cost of Waste plastic = Rs. 5/- per Kg

Cost of bitumen = Rs. 50/- per Kg

Generally, for 1 Km of road 10 tons of bitumen is required.

Cost of bitumen per Km = 50 × 100000 = 50,0,000/-

For plastic coated bituminous road,

It is already discussed above that 10% of plastic is required.

Amount of bitumen required for Plastic coated bituminous road = 9000Kg

Amount of plastic required = 1000Kg

Cost of bitumen in plastic coated bituminous road + Cost of plastic required = 9000×50+5,000

Total cost = 4,55,000/-

Savings in construction per Km = (cost of bitumen per ordinary road - cost of plastic-coated bituminous road per Km)

= 5,00,000 - 4,55,000

= 45,000/- per Km

2.      Advantages:

·        Disposal of waste plastic will no longer be a problem.

·        The up-gradation cost is less compared to normal roads.

·        The load with standing property also increased.

·        The cost of road construction also reduced.

·        Road strength also increases.

·        Plastic roads could have a hollow space to facilitate wiring, pipe lines, etc.

·        Plastic roads have less moisture absorption than normal roads.

·        Better resistance to rain water and stagnation.

·        Increases binding strength of the aggregate and bitumen.

·        Durability of road is increases when compared to normal road.

·        Reduced construction time on site

3.       Disadvantages:

·        The heat treatment of plastic may lead to release of harmful gases to atmosphere.

·        Roads made of pure plastic may leads to decrease in strength with small variation in temperature.

·        The plastic may break into micro plastic particles due to atmospheric oxidation.

6.       CONCLUSION

            The generation of waste plastics is increasing day by day. The plastics show adhesion property in their molten state. Plastics will increase the melting point of the bitumen. Hence, the use of waste plastics for pavement is one of the best methods for easy disposal of waste plastics. Moreover, plastic is not recyclable and using them in road construction will help in the disposal of these plastic wastes in an eco-friendly manner. The plastic-coated bitumen increases the melting point. Polymer Modified Bitumen is used due to its better performance. The plastic-coated bitumen helps in binding strength and increases the area of contact between the aggregate and bitumen. It also helps in eliminating of the voids. Due to the elimination of voids, road show the resistance towards the oxidation of bitumen by entrapped air. This property makes the plastic-coated bitumen road to withstand heavy traffic and show better durability

            Plastic roads will be most feasible for a country like India, where temperature is around 50ËšC and the heavy monsoons too create havoc, leaving the roads with potholes and ruts. It is hoped that in near future we will have strong, durable and eco-friendly roads that will relieve the earth from all type of plastic waste.