Abstract
The practical application of waste materials such as steel furnace slag (SFS) and coal wash (CW) is becoming more prevalent in many geotechnical projects. It was found that the inclusion of rubber crumbs (RCs) from recycled tyres into mixtures of SFS and CW not only solves the problem of large stockpiles of waste tyres, it also can provide an energy-absorbing medium that will reduce track degradation. In order to investigate the influence of RC on the geotechnical properties of the granular waste matrix (SFS+CW+RC), a series of monotonic consolidated drained triaxial tests were conducted on waste mixtures. The test results reveal that the inclusion of RC significantly affects the geotechnical properties of the waste mixtures, especially their critical state behaviour. Specifically, the waste matrix can achieve a critical state with a low RC content (<20%), whereas those mixtures with higher RC contents (20-40%) cannot attain a critical state within the ultimate strain capacity that can be applied to specimens using the traditional triaxial equipment. Therefore, for the waste matrix with higher RC contents extrapolation of the measured volumetric strains had to be adopted to obtain the appropriate critical state parameters. Moreover, the influence of energy absorbing property by adding RC on the critical state behaviour has also been captured through an empirical equation.
Highlights
The stockpiles of end-of-life tyres keep mounting worldwide
Senetakis et al [4] stated that the damping property of sand-rubber mixtures could be enhanced by increasing the rubber content, while Indraratna et al [5] demonstrated the role of a synthetic energy absorbing layer (SEAL) is in lieu of conventional capping material by mixing 10% rubber crumbs (RCs) with steel furnace slag (SFS) and coal wash (CW)
The critical state behaviour of the SFS+CW+RC mixtures was investigated through a series of monotonic, consolidated-drained triaxial tests
Summary
The stockpiles of end-of-life tyres keep mounting worldwide. It was reported that around 51 million equivalent passage units of waste tyres were generated in 2013-14 period alone in Australia, which exceeds 400,000 tonnes, of which only about 5% was properly recycled [1]. Stockpiling of waste tyres is highly undesirable because of the risk of combustion under high heat, health risks (e.g. breeding of mosquitoes) and obvious environmental pollution. From both environmental and economical perspectives, there is a pressing need to encourage innovative recycling solutions of scrap tyres. The high damping characteristics of rubber materials have made them promising materials to be included in geo-infrastructure to increase energy absorbing capacity (increased ductility), and reduce vibration and noise in transport corridors. The investigation of the influence of RC content (RRbb, %) on the critical state behaviour of the rubber-soil mixtures from a fundamental (mathematical) insight is limited. The relationship between the energy absorbing capacity and the critical state parameters will be explored and quantified
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