17-10-2016, 11:10 AM
1459344835-USAGEOFPLASTICWASTEINROADCONSTRUCTION.docx (Size: 114.82 KB / Downloads: 7)
Abstract
Now-a-days Plastic is everywhere in today’s lifestyle. The disposal of plastic wastes is a great problem. These are non-biodegradable product due to which these materials pose environmental pollution and problems like breast cancer, reproductive problems in humans and animals, genital abnormalities and even a decline in human sperm count and quality. In recent years, applications of plastic wastes have been considered in road construction with great interest in many developing countries. The use of these materials in road making is based on technical, economic, and ecological criteria. Several million metric tons of plastic wastes are produced in India every year. If these materials can be suitably utilized in highway road construction, the pollution and disposal problems may be partly reduced. Keeping in mind the need for bulk use of these wastes in India, it was thought expedient to test these materials and to develop specifications to enhance the use of plastic wastes in road making, in which higher economic returns may be possible. The possible use of these materials should be developed for construction of low-volume roads in different parts of our country. A review of various plastic wastes for use in the construction of roads has been discussed in this paper.
Introduction
Plastic is everywhere in today’s lifestyle. It is used for packaging, protecting, serving, and even disposing of all kinds of consumer goods. With the industrial revolution, mass production of goods started and plastic seemed to be a cheaper and effective raw material. Today, every vital sector of the economy starting from agriculture to packaging, automobile, building construction, communication or InfoTech has been virtually revolutionized by the applications of plastics. Use of this non-biodegradable (according to recent studies, plastics can stay unchanged for as long as 4500 years on earth) product is growing rapidly and the problem is what to do with plastic-waste. Studies have linked the improper disposal of plastic to problems as distant as breast cancer, reproductive problems in humans and animals, genital abnormalities and even a decline in human sperm count and quality. If a ban is put on the use of plastics on emotional grounds, the real cost would be much higher, the inconvenience much more, the chances of damage or contamination much greater. The risks to the family health and safety would increase and, above all the environmental burden would be manifold. Hence the question is not ‘plastics Vs no plastics’ but it is more concerned with the judicious use and re-use of plastic-waste.
In recent years, applications of plastic wastes have been considered in road construction with great interest in many developing countries. The use of these materials in road making is based on technical, economic, and ecological criteria. The lack of traditional road materials and the protection of the environment make it imperative to investigate the possible use of these materials carefully India has a large network of metro cities located in different parts of the country and many more are planned for the near future. Several million metric tons plastic wastes are produced every year in India.
Traditionally soil, stone aggregates, sand, bitumen cement etc. are used for road construction. Natural materials being exhaustible in nature, its quantity is declining gradually. Also, cost of extracting good quality of natural material is increasing. Concerned about this, the scientists are looking for alternative materials for highway construction, and plastic wastes product is one such category. If these materials can be suitably utilized in highway construction, the pollution and disposal problems may be partly reduced. In the absence of other outlets, these solid wastes have occupied several acres of land around plants throughout the country. Keeping in mind the need for bulk use of these solid wastes in India, it was thought expedient to test these materials and to develop specifications to enhance the use of these plastic wastes in road making, in which higher economic returns may be possible. The possible use of these materials should be developed for construction of low-volume roads in different parts of our country. The necessary specifications should be formulated and attempts are to be made to maximize the use of solid wastes in different layers of the road pavement
On heating at 100 - 160°C, plastics such as polyethylene, polypropylene and polystyrene, soften and exhibit good binding properties. Blending of the softened plastic with bitumen results in a mixed that is amenable for road laying. The mix has been used to lay road of length up to 1,500 km in the state of Maharashtra. Other states like Tamil Nadu, Karnataka, Pondicherry, Kerala and Andhra Pradesh have also laid test roads. These roads have withstood loads due to heavy traffic, rain and temperature variation
Plastic Waste Scenario
The use of plastic materials such as carry bags, cups, etc. is constantly increasing. The consumption of plastics have increased from 4000 tons/annum (1990) to 4 million tons/annum (2001) and it is expected to rise 8 million tons/annum during the year 2009. Nearly 50 to 60% of the total plastics are consumed for packing. Once used plastic materials are thrown out. They do not undergo bio-decomposition. Hence, they are either land filled or incinerated. Both are not eco-friendly processes as they pollute the land and the air. Any method that can use this plastic waste for the purpose of construction is always welcomed.
Plastic Wastes used in process
The following types of waste plastic can be used in the construction of rural roads:
• Films ( Carry Bags, Cups) thickness up to 60micron (PE, PP and PS)
• Hard foams (PS) any thickness
• Soft Foams (PE and PP) any thickness.
• Laminated Plastics thickness up to 60 micron (Aluminum coated also) packing materials used for biscuits, chocolates, etc.,
• Poly Vinyl Chloride (PVC) sheets or Flux sheets should not be used in any case.
Characteristics of Plastic Waste
Thermal study
A study of the thermal behavior of the polymers namely polyethylene, polypropylene, polystyrene shows that these polymers get softened easily without any evolution of gas around 130-1400C, this has been scientifically verified. At around 3500C, they get decomposed releasing gases like methane, ethane etc. and above 7000C, they undergo combustion producing gases like CO and CO2.
Binding property
The molten plastic waste inhibits good binding property. Following experiments were carried out to study the binding property.
The aggregate was heated to around 1700C and the shredded plastic waste (size between 2.36mm and 4.75 mm) was added. Plastics got softened and coated over the aggregate. The mix of aggregate and plastic was compacted and cooled. The block was very hard and showed compressive strength not less than 130 MPa and binding strength of 500 kg/cm2. This shows that the binding strength of the polymer is good.
The polymer coated aggregate was soaked in water for 72 hours. There was no stripping at all. This shows that the coated plastic material sticks well with the surface of the aggregate.
Characterization of Plastic Waste-Bitumen Blend for Flexible Pavement
The utility of the plastic waste blended bitumen-aggregate mix for flexible pavement construction was characterized by studying stripping value and Marshall Stability value of the mix for the blends having a maximum of 1.5% plastic waste.
1. Stripping Test (IS :6241-971)
Plastic waste was dissolved in bitumen and the blend was coated over aggregate. It was tested by immersing in water. Even after 72 hrs, there was no stripping. This shows that the blend has better resistance towards water. This may be due to better binding property of the plastic waste-bitumen blend.
2. Marshall Stability Test
The specimen was prepared as per the IRC specification using plastic waste-blended bitumen. This shows that plastic waste-bitumen blend has higher strength compared to pure bitumen, whose value is approx. 1200Kg. Moreover, the Marshall Quotient is also within the range of tolerance, thus showing that the plastic waste (polyethylene) blended bitumen mix is better and more suitable for flexible pavement construction.
Results of Preliminary Studies
The studies of properties of the plastic waste-blended bitumen show that the addition of plastic waste to bitumen increases softening point, decreases penetration value and ductility, increases flash point and fire point, increase Marshall stability value and improve anti-stripping properties. Yet the above process has its own limitations
1. The preparation of such modified bitumen needs high power stirrer with thermostatic facilities to maintain the temperature between160-1800C. Any increase in the temperature could affect the properties of bitumen.
2. The proper storage of such polymer-blended bitumen is very important. It should be stored in a freezer and it is also referred that it is stable for 6 hrs at a temperature of 1800C
3. It was also observed from the separation test that when the plastic was mixed beyond the soluble range (from 2% and above) the excess plastic material got separated on cooling.
These limitations necessitated developing an alternate method for using higher percentage of plastic waste for flexible pavement.
Modified Process (Dry Process)
An alternate method was innovated to find an effective way of using higher percentage of plastic waste in the flexible pavement. The aggregate coated with plastic was used as the raw material. The plastic used were the disposed carry bags, films, cups was etc. with a maximum thickness of 60 microns. The bitumen was not blended with plastic waste.
Preparation of Polymer-Aggregate-Bitumen Mix
Step 1:
Plastics waste (bags, cups, thermocole) made out of PE, PP and PS cut into a size between 2.36mm and 4.75mm using shredding machine, (PVC waste should be eliminated).
Step 2 a:
The aggregate mix is heated to 165°c (as per the HRS specification) and transferred to mixing chamber.
Step 2 b:
Similarly the bitumen is to be heated up to a maximum of 160°c (HRS Specification) to have good binding and to prevent weak bonding. (Monitoring the temperature is very important).
Step 3:
At the mixing chamber, the shredded plastics waste is to be added. It gets coated uniformly over the aggregate within 30 to 60 seconds, giving an oily look.
Step 4:
The plastics waste coated aggregate is mixed with got bitumen and the resulted mix is used for road construction. The road laying temperature is between 110°c to 120°c. The roller used is 8-ton capacity.
Characterization of PCA Bitumen Mix
1. Stripping Test (IS: 6241-1971).
The plastic waste coated aggregate bitumen mix prepared by the above process was immersed in water. Even after 96 hours there was no stripping. This shows that the plastic waste coated aggregate-bitumen mix has good resistance towards water.
2. Marshall Stability Test
It is observed that the Marshall Stability values obtained for were generally much higher than the Marshall Stability value obtained for pure bitumen min.
3. Field study
Using this dry process technique, road length of more than 1200 km were laid at different places in Tamil Nadu both by the department of Rural Development Agency and by Highways at Cochin, Mumbai, and Pondicherry the corporation laid test roads using this technology. The roads are exposed to heavy traffic, monsoonal change, heavy rain, hot summer etc. The roads are functioning well without potholes, raveling and rutting. Expert’s opinions are also in agreement.
4. Water absorption test
A known quantity of aggregate was taken dried at 1100C and cooled. The weight of aggregate was determined. It was then immersed in water for 24 hrs. Then the aggregate was dried using dry clothes and the weight was determined. The water absorbed by the aggregate was determined from weight difference. 500gms of the aggregate was taken and heated to around 1700C. It was then coated with plastic at that temperature. The plastic coated aggregate was cooled to room temperature. It was immersed in water for 24 hrs. Then it was removed dried and the weight of the aggregate was determined. It is observed that the absorption of water had decreased with the increase in the percentage coating of plastic over the aggregate. This shows that the coating of plastic reduces the voids. Hence, coating of plastic over aggregate helps to improve the quality of the aggregate.
Method of Road Laying.
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 1650c (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 melts and gets coated over the aggregate, thus forming an oily coating.
Similarly, the bitumen is to be heated to a maximum of 1600c 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 1100c to 1200c. The roller used is normal 8-ton capacity.
For intensive works Central Mixing Plant can also be used. The operating Techniques for this are given below:
The aggregate materials will be transferred to the cylinder through the conveyer belt.
• The shredded plastics will be sprayed over the aggregate while it is moving in the conveyer belt.
• The spraying is done by manual labors standing up on both side of the conveyer belt of the central mixing plant.
• The addition of plastics should be done quantitatively.
The amount of binder to be added is calculated and monitored:
In the central mixing plant, at the control room the addition of bitumen is monitored.
It is easy to know the amount of bitumen sprayed per minute inside the cylinder.
Amount of plastic to be added is @8% of bitumen.
For example if the bitumen quantity per minute is 10Kg, the plastic need to be added is 0.8 Kg. i.e. (A bucket can be used which can hold 0.8 Kg at a time)
Now, as the aggregate moves in the conveyer belt, the shredded plastics, taken in the bucket are sprayed with a speed of 0.8 Kg/1min with suitable mechanical device or manually.
In manual method, one person will be adding the shredded plastic on to the conveyer belt. In the mean time another person will keep ready another bucket full of plastics so that the addition of plastics will be continuous. Thus manual labor can also be so chosen that the addition is done continuous. Two or three labors will be on this work of addition of plastics. As the plastics is added over the aggregate, the mix (aggregate and plastics) moves into the cylinder. As the stone is heated the plastic films get melted over the heated stone and get coated. Slowly the plastics coated aggregate moves forward where this polymer coated aggregate is mixed with bitumen. The polymer coated aggregate bitumen mix is then transferred to the dipper.
Advantages of Central Mixing Plant
1. Mixing of the plastics over the aggregate is uniform
2. The coating is better and the mixing of bitumen is being carried out at places like.
Inside the Cylinder
During loading in the dipper.
During transferring the mix in the paver
During the spreading of the mix by the paver
Hence better distribution takes place in the Central Mixing Plant Process
Economic considerations
It has been found that modification of bitumen with shredded waste plastic marginally increases the cost by about Rs. 2500 per tonne. However this marginal increase in the cost is compensated by increase in the volume of the total mix, thereby resulting in less overall bitumen content, better performance and environmental conservation with usage of waste plastic.
Salient Features of the Polymer-Waste-Bitumen Mix Road
• Road strength 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
• Simple process without any industry involvement
• In situ process
• Use of plastics waste for a safe and eco-friendly process
• Both Mini Hot Mix Plant and Central Mixing Plant can be used
• Only aggregate is polymer coated and bitumen is not modified
• Use 60/70 and 80/100 bitumen is possible
• No evolution of any toxic gases like dioxin
It is observed that addition of plastics waste up to 10 - 15% by weight of bitumen resulted into higher values of softening point and lower values of penetration, which are appreciable improvements in the properties of the binder. This has resulted and withstood higher traffic load and high temperature variation. Several experimental stretches have been laid in more than 15 locations in Tamilnadu using both Mini hot-mix and central mixing plants.
Advantages of Plastic Tar Road
A well constructed Plastic Tar Road will result in the following advantages.
• 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 raveling.
• 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 UV.
DISADVANTAGES OF PLASTIC ROADS
1. Cleaning process
Toxics present in the co-mingled plastic waste would d start leaching.
2. during the road laying process
But the presence of chlorine will definitely release noxious HCL gas.
3. after the road laying
The components of the road, once it has been laid, are not inert. It is opined that the first rain will trigger leaching. As the plastics will merely form a sticky layer, (mechanical abrasion). once the road is started to be used will cause the release of fine polymer particles. When air-borne, these will cause a particulate problem.
Comparison
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 tones 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 kilometer 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.
Results and Discussion
Preliminary studies on the use of plastic-waste as a blending material with bitumen, suggest that the blends behave similar to PMB, thus having improved properties compared to plain bitumen. It is also observed that this process of blending has limitation. At high percentage of blending there is separation of plastic. Hence, process modification was needed and a new product namely plastic waste coated aggregate was developed. This product is not only easy to prepare but also helps to use higher percentage of plastic-waste for coating without much of difficulty.
The coating of molten-plastic over the aggregate will reduce water absorption. This shows that the voids at the surface were reduced. Lesser the voids better the quality of the aggregate. Otherwise, the air entrapped in the voids would cause oxidation of bitumen resulting in stripping, pothole formation etc. Moreover, the presence of water in the voids is detrimental to adhesion between aggregate and the binder namely bitumen. Hence the aggregate with lesser voids is considered to be good for better road construction. These observations help to conclude that plastic-waste coated aggregate can be considered as more suitable material for flexible pavement construction.
Conclusion
Polymer Modified Bitumen is used due to its better performance. But in the case of higher percentage of polymer bitumen blend, the blend is a more polymer dispersion in bitumen, which get separated on cooling. This may affect the properties and quality of the blend and also the road laid using such blend.
In the modified process (dry process) plastics-waste is coated over aggregate. This helps to have better binding of bitumen with the plastic-waste coated aggregate due to increased bonding and increased area of contact between polymer and bitumen. The polymer coating also reduces the voids. This prevents the moisture absorption and oxidation of bitumen by entrapped air. This has resulted in reduced rutting, raveling, and there is not pothole formation. The road can withstand heavy traffic and show better durability.
References