This article is presented by:D S V Prasad, Member
Dr G V R Prasada Raju, Member
Dr V Ramana Murthy, Non-member

Use of Waste Plastic and Tyre in Pavement Systems

ABSTRACT

Expansive soils are so widespread that it becomes impossible to avoid them for highway construction. Many highway agencies, private organizations and researches are doing extensive studies on waste materials and research projects concerning their feasibility and environmental suitability. This paper describes the attempts made to investigate the stabilisation process with model test tracks over expansive subgrade. Shear, CBR and loading-unloading tests were carried out on the tracks with different reinforcement materials, nemely, waste plastics and waste tyre rubber introduced in gravel subbase course laid on expansive subgrade. Test results show that enhanced load carrying capacity is obtained for reinforced gravel subbase as compared to unreinforced gravel subbase in the flexible pavement system.

INTRODUCTION
Expansive soils are generally found in poorly drained localities where there are marked wet and dry seasons. Differential thermal analysis (DTA) and X-ray diffraction pattern analysis1,2 have shown that montmorillonite is the predominant clay mineral in black cotton soil. The high percentage of clay content with predominant montmorillonite mineral is responsible for high volumetric changes during wetting and drying. These volumetric changes cause huge damage to all civil engineering structures such as road pavements resting on them. Reinforcement of soils with natural and synthetic fibres is potentially an effective technique for increasing soil strength. In the recent years, this technique has been suggested for a variety of geotechnical applications ranging from retaining structures, earth embankments and footings to subgrade/subbase stabilisation of pavements3–10 demonstrated the capability of synthetic fibre reinforcement for improving the behavior of sand by using triaxial tests, CBR tests, cyclic triaxial tests, resonant-column and torsional shear tests. These studies indicated that fibre inclusions increase the ultimate strength, stiffness, CBR, resistance to liquefaction, shear modulus and damping of reinforced sand. Gray and Ohashi3, Gray and Maher11 conducted the direct shear tests on quartz sand specimens reinforced with dry fibres and concluded that the fibre reinforcement generally increases the ultimate shear strength and also limits the reduction in the post-peak shearing resistance of the soil specimen. Scrap tyres are a type of waste material for which several beneficial uses have been proposed and put into practice12. The use of tyre shreds or mixtures of tyre shreds and sand (ie, rubber-sand) as lightweight fill13 could provide an alternate avenue for waste tyre disposal. Using shredded waste tyres as a lightweight fill material for road construction has proven to be another beneficial use of this waste product. Al Wahab14 based on his experience in admixture and reinforcement testing, found that the typical sizes of laboratory specimens do not allow for consistent mixing of the shreds within the soil matrix. Lee, et al 15 also used tyre chips, which was defined as shreds that had maximum dimensions of 12 mm to 50 mm. The authors were able to obtain consistent results of strength gain through triaxial testing. However, not much research work has been reported on the gravel subbase reinforced with waste plastic and waste tyre rubber for its application in flexible pavements on expansive soil subgrade. In the present work an attempt has been made to reinforce gravel subbase with waste plastics and waste tyre rubber separately in the model flexible pavement system laid on expansive soil subgrade.

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