Waste Plastic Bags in
Bituminous Mix for
Improved Performance of Roads
Centre for Transportation Engineering, Bangalore University, Bangalore, India [Unpublished] Apr02
Prof. C.E.G. Justo Honorary Professor, Bangalore University Bangalore and
Dr. A. Veeraragavan Co-ordinator, Centre for Transportation Engineering, Bangalore University, Bangalore - 560 0056
The growth in various types of industries together with population growth has resulted in enormous increase in production of various types of waste materials, world over. The creation and disposal of non-decaying waste materials such as Blast Furnace Slag, Fly-ash, Steel Slag, Scrap Tyres, Plastics, etc. have been posing difficult problems in developed as well as in developing countries. Considerable work has been done in various countries for the disposal of some of these waste products and utilisation of some other products and there is a long list of published literature dealing with different aspects of these challenging problems(1). Attempts are still being made by various organisations and researchers to find methods for effective utilisation of some of these waste materials. Of these, the efforts to find useful applications of some of the waste products in highway construction have given encouraging results (1). The work done in India, particularly at the Central Road Research Institute (CRRI), New Delhi on the use of waste materials like Fly-ash and Slag in road construction is note worthy.
The use of thin plastic bags to pack and to carry various materials including house hold articles has become a common practice all over the country. However the disposal of the waste plastic bags in large quantities has been a problem and is of great concern, particularly in big cities. The mixing up of these waste plastic bags with other bio-degradable organic waste materials in the garbage of the urban areas has been the main cause of the problem. Therefore attempts are being made in some cities to limit or even to prohibit the use of the thin plastic bags for packing and other common use, so as to control this "undesirable waste material" from getting mixed up with the other organic garbage.
In case it is possible to find useful application for the waste plastic bags, there will be substantial scrap value for this waste product and therefore they will be collected and sold by interested persons, instead of being littered or thrown out in the dust bins or into the road side drains.
At the initiative of M/s K.K. Poly Flex Pvt. Ltd., a study on the possible use of the processed plastic waste bags with the bituminous mixes was carried out at the R.V. College of Engineering Bangalore. A group of students of B.E. degree course in Chemical Engineering of this college under the guidance of the concerned teaching staff carried out their final year project work for studying the possibility of using of the processed plastic bags with bitumen and bituminous mixes(2). As some encouraging results were reported in this study, M/s K.K. Poly Flex Pvt. Ltd. later approached the Centre for Transportation Engineering of Bangalore University with the request to carry out further research studies on the effects of using the processed plastic bags with bituminous mixes for road construction works. This company supplied the processed plastic material and they also helped the Centre for developing some additional facility to test the bituminous mix specimens under controlled temperature.
2. USE OF RE-CYCLED PLASTICS AS ADDITIVES IN BITUMINOUS MIXES
It has been possible to improve the performance of bituminous mixes used in the surfacing course of road pavements, with the help of various types of additives to bitumen such as polymers, rubber latex, crumb rubber- treated with some chemicals, etc. Some limited studies have been reported on the use of re-cycled plastic, mainly polyethylene, in the manufacture of polymer - modified asphalt cement or bitumen. According to Larry Flynn (3), re-cycled polyethylene from grocery bags may be useful in asphaltic (bituminous) pavements, resulting in reduced permanent deformation in the form of rutting and reduced low - temperature cracking of the pavement surfacing.
Salah E. Zoorob (4) and Zoorob and Suparma (5) have shown that re-cycled plastics composed predominantly of polypropylene and Low Density Polyethylene can be incorporated into conventional asphaltic (bituminous) road surfacing mixtures. Greater durability and fatigue life have been reported in these modified mixes as compared to conventional mixes.
3. RECENT STUDIES ON THE USE OF PROCESSED PLASTIC BAGS IN BITUMINOUS CONCRETE MIXES
3.1 General Findings
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(6). 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.
Studies were carried out on Bituminous Concrete (BC) mixes using 80 / 100 grade bitumen having average Marshall Stability Value (MSV) of 1100 kg at optimum bitumen content of 5.0 % by weight of the mix. Further studies on BC 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 BC mix using the modified binder was found to be as high as 3312 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 BC 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.
Thus the laboratory investigations carried out so far at Bangalore University have given highly encouraging results for the use of bituminous concrete mixes in the surfacing course of road pavements by using this modified binder which is prepared by the addition of 8.0 % of the processed plastic, by weight of bitumen. 3.2. Advantages of Using Modified Bitumen with Processed Plastic as Additive
i) The use of modified bitumen with the addition of processed plastic, about 8.0 % by weight of bitumen, helps in substantially improving the stability or strength, fatigue life and other desirable properties of bituminous concrete mix, even under adverse water-logging conditions. Therefore the life of the pavement surfacing course using the modified bitumen is also expected to increase substantially in comparison to the use of ordinary bitumen.
ii) The addition of 8.0 % by weight of processed plastic for the preparation of modified bitumen results in a saving of 0.4 % bitumen by weight of the mix or about 9.6 kg bitumen per cubic metre (m 3) of BC mix. This results in a saving of about Rs.110 per m 3 of BC mix based on the present cost of 80 / 100 grade bitumen, ( as of June, 2001 ).
iii) The effective utilisation of the waste plastic bags for the preparation of modified bitumen will result in substantial increase in the scrap value for this other wise "undesirable waste material", which are getting littered all over the urban areas. These waste plastic bags will not therefore be thrown out along with the garbage; instead they will get collected and sold by the consumers themselves or other agencies, due to the attractive scrap value.
4. NEED FOR FURTHER WORK
It is necessary to work out a project proposal to carry out further studies on various aspects such as collection, processing and effective utilisation of this waste material. To start with, such a study could be initiated in Bangalore, with the following components :
i) Estimation of the types, quantity and useful components present in the waste plastic materials in the city and surrounding areas
ii) Methodology for collection and sorting out the useful components of the plastic waste
iii) Methodology for processing the plastic bags as required for use in the preparation of modified bitumen, including cleaning, shredding and further processing of the plastic waste materials
iv) Identification of two or three construction companies / entrepreneurs who could incorporate appropriate mixing units in their bitumen boiler / hot mix plant to add and mix the required proportion of the processed plastic additive
v) Carrying out further laboratory investigations, construction of some test tracks and field studies on the performance of pavements using the modified bitumen
vi) Working out relative economics of using the modified bituminous mixes in road construction works, considering the improved performance and increased service life of the pavement
vii) Preparation of specifications and standards for the construction industry.
It is hoped that on completion of the above project, the plastic waste materials will be put to effective use in road construction industry, resulting in improved road pavements and also relief from the waste plastic materials being littered all around urban areas.
5. SOME SELECTED REFERENCES
1. Robin L Schroeder, "The Use of Recycled Materials in Highway Construction", Journal, Public Roads, Vol. 58, No. 2 (1994 )
2. Amjad Khan, Gangadhar, Murali Mohan and Vinay Raykar, "Effective Utilisation of Waste Plastics in Asphalting of Roads". Project Report prepared under the guidance of R. Suresh and H. Kumar, Dept. of Chemical Engg., R.V. College of Engineering, Bangalore, 1999.
3. Larry Flynn, "Recycled Plastic Finds Home in Asphalt Binder", Journal, Roads and Bridges, March 1993
4. Zoorob S.E. and Suparma, L.B., "Laboratory Design and Investigation of Proportion of Bituminous Composite Containing Waste Recycled Plastics Aggregate Replacement (Plastiphalt), CIB Symposiumon Construction and Environment Theory into Practice, Sao Paulo, Brazil ( November, 2000 )
5. Zoorob, S.E., "Laboratory Design and Performance of Improved Bituminous Composites Utilising Plastics Packaging Waste", Conference on Technology Watch and Innovation in Construction Industry, Belgium, Building Research Institute, Brussels, Belgium (April, 2000)
6. Research Work at the Centre for Transportation Engineering, Bangalore University during the year 2000 - 2001 and the Seminar Report on "Study of the Effect of Plastic Modifier on Bituminous Mix Properties" by V.S. Punith, II Semester, M.E. (Civil) Highway Engg., Dept. of Civil Engineering, Bangalore University (March, 2001)
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