A STUDY ON INFLUENCE OF WASTE RUBBER TYRE CRUMBS ON STRENTH OF SOIL

Abstract

Tyres used in automobile industries get converted into waste tyres as soon as their treads are worn out. Hence, every year there is an increase in the waste tyres worldwide. As a result, their disposal has become one of the major environmental problems. Millions of discarded tyres are rejected in large piles across the land of a territory as well as dumped in large amount in the landfills every year. These are a threat to the environment because they lead to environmental pollution as well as have a potential to cause fire and health hazards. Being light in weight and having low density as compared to other waste materials, they require a larger volume of landfills. Therefore, the effective re-utilization of waste tyres has attracted the researchers towards itself since the last 2-3 decades. Worn out tyres can be used in a number of ways to reduce environmental problems. Some studies have shown that such tyres in the form of shreds and chips provide a lightweight construction material which generally improves the engineering properties of soils, such as strength, bearing capacity, and CBR values. In the present study an attempt has been made to use the waste rubber tyre crumbs which are small shredded pieces of waste rubber tyres coming to the workshop from dump yards. The crumbs were passed through I.S. 2.8 mm sieve (coarse-grained tyre crumbs) and added in soil samples in proportions of 4%, 8%, 12% and 16% by weight of soil measured dry. OMC and MDD of all the soil-tyre crumb mixtures were determined using heavy compaction and the mixtures were tested for un-soaked CBR values. The test results indicated an improvement in the CBR value at varying proportions of tyre crumbs, 8% being witnessed to report an overall increment of 17.28 (i.e., 122.6% increase) in the CBR value of the soil taken which showed similarity to some previous researches done and supports the method of re-utilizing the cheap waste tyre crumbs as a soil stabilizer which may be useful, for example, in reducing the thickness of filling material required in construction works and the thickness of pavements. For determining shear strength, Unconfined Compressive Strength test was performed on the clayey soil. The crumbs were passed through I.S. 2 mm sieve (medium-grained tyre crumbs) and added in soil samples in proportions of 2%, 4%, 6%, 8% and 10% by weight of soil measured dry. The test results indicated an overall increase in the UCS value as well as shear strength value by 19.25% which were very much similar to those obtained in previous studies. This proves the rubber tyre crumbs to be an effective fill material in back-fills behind retaining structures, bridge abutments and highway embankments. iv Further, geo-chemical analysis of the test materials and their composite mixture was done. This includes SEM (Scanning Electron Microscopy), XRD (X-Ray Diffraction) and FTIR (Fourier Transform Infrared spectroscopy). The SEM test resulted that the morphology of the tyre crumbs was such that fibers similar to the follicles of hair were depicted which bind the soil with the rubber crumbs for long. XRD patterns showed amorphous and crystalline behavior of the samples and also some major minerals found therein. Bonds were identified by FTIR analysis which showed that the compounds found in the soil and rubber tyre individually were also present in the composite of the two. Thus, the stabilization of soil with rubber tyre crumbs can be said to be beneficial in an overall context.