Steel furnace slag (SFS) and coal wash (CW) are two common by-products from the coal-mining and steel industries in Australia. Rubber crumbs (RC) is a material derived from waste tires contributing to environmental problems in most developed countries. Reusing and recycling these waste materials is not only economically beneficial and environmentally sustainable, but it also helps to address geotechnical problems such as track degradation. In this study, SFS, CW, and RC are blended to explore the feasibility of obtaining an energy-absorbing capping layer with properties similar or superior to conventional subballast. Comprehensive laboratory investigations have been carried out to study the geotechnical properties of SFS + CW + RC mixtures, from which seven parameters (including gradation, permeability, peak friction angle, breakage index, swell pressure, strain energy density, and axial strain under cyclic loading) were used to evaluate the properties of these mixtures used as subballast. It was found that a mixture with SFS∶CW = 7∶3 and 10% RC (63% SFS, 27% CW, and 10% RC) is the best mixture for subballast.Abstract: Steel furnace slag (SFS) and coal wash (CW) are two common by-products from 37 coal mining and steel industries in Australia. Rubber crumbs (RC) is a material derived from 38 waste tyres contributing to environmental problems in most developed countries. Reusing and 39 recycling these waste materials is not only economically beneficial and environmentally 40 sustainable, but it also helps to address geotechnical problems such as track degradation. In 41 this study, SFS, CW, and RC are blended to explore the feasibility of obtaining an energy 42 absorbing capping layer with properties similar or superior to conventional subballast. 43Comprehensive laboratory investigations have been carried out to study the geotechnical 44 properties of SFS+CW+RC mixtures, from which seven parameters (including gradation, 45 permeability, peak friction angle, breakage index, swell pressure, strain energy density, and 46 axial strain under cyclic loading) were used to evaluate the properties of these mixtures used 47 as subballast. It was found that a mixture with SFS:CW=7:3, and 10% RC (63% SFS, 27% 48 CW, and 10% RC) is the best mixture for subballast. 49 KEYWORDS: Steel furnace slag; coal wash; rubber crumbs; subballast; reuse and recycling 50 of waste materials 51 52 53 CW and SFS are granular by-products of the coal mining and steel industries, respectively.54

The practical application of waste materials such as steel furnace slag (SFS) and coal wash (CW) is becoming more prevalent in many geotechnical projects. While adding rubber crumbs (RCs) from recycled tires into mixtures of SFS and CW not only solves the problem of large stockpiles of waste tires, it also can provide an energy-absorbing medium that will reduce vibration and prevent track degradation. Thus, the engineering insight into the effect that rubber crumbs have on the dynamic behavior of SFS þ CW þ RC mixtures is in urgent demand. In this study the influence that RC contents and confining pressures have on the deformation, resilient modulus, damping ratio, and shear modulus was investigated by cyclic triaxial tests. Test results reveal that with the inclusion of RC, the axial strain, volumetric strain, damping ratio, and energy-absorbing capacity of the SFS þ CW þ RC mixture increase, while its resilient modulus and shear modulus decrease. Based on these properties, an amount of 10% RC is recommended as an optimal blended mix to be used as railway subballast. A three-dimensional (3D) empirical model of the relationship between the maximum axial strain, volumetric strain, and resilient modulus with RC contents and the effective confining pressure was developed, and the energy-absorbing capacity of these waste mixtures has also been analyzed for practical purposes based on their comprehensive parameters.

The influence of rubber crumbs on the dilatancy behavior and critical state of steel furnace slag (SFS), coal wash (CW), and rubber crumbs (RC) mixtures was investigated via a series of monotonic drained triaxial tests. These tests revealed that RC contents (R b , %) have a significant influence on the dilatancy behavior and critical state of the aforementioned waste mixtures; in fact, as more R b is added, dilatancy and the slope of the critical state line in e−ln p′ space decreases. Within the framework of critical state soil mechanics, a dilatancy model for SFS+CW+RC mixtures was proposed and validated using experimental data. This model also captured the energy-absorbing property of RC using an empirical relationship between the total work input W total and the critical stress ratio M cs . Abstract:The influence of rubber crumbs on the dilatancy behavior and critical state of 37 SFS+CW+RC mixtures (i.e., blends of steel furnace slag, coal wash, and rubber crumbs) has 38 been investigated via a series of monotonic drained triaxial tests. These tests reveal that RC 39 contents (ܴ , %) have a significant influence on the dilatancy behavior and critical state of 40 the aforementioned waste mixtures; in fact as more ܴ is added, dilatancy and the slope of 41 the critical state line in ݁ − ln ‫′‬ space decreases. Within the framework of critical state soil 42 mechanics, a dilatancy model for SFS+CW+RC mixtures has been proposed and validated 43 using experimental data. This model also captured the energy absorbing property of RC using 44 an empirical relationship between the total work input ܹ ௧௧ and the critical stress ratio ‫ܯ‬ ௦ . 45 KEYWORDS: Steel furnace slag; coal wash; rubber crumbs; critical state; energy absorbing 46 property; dilatancy 47 48 Steel furnace slag (SFS) and coal wash (CW) are waste by-products of steel making and coal 49 mining, whereas rubber crumbs (RC) are derived from waste tires, and since they occupy 50 large amounts of useable land their long term effect on the environment is extremely 51 detrimental. One of the best ways of dealing with these materials is to recycle them into 52 geotechnical projects such as port reclamations, where different blends of SFS+CW have 53 already been used successfully (Chiaro et al., 2013). However, while incorporating RC into 54 SFS+CW blends can further reduce the particle breakage of CW and swelling of SFS, as well 55 as increasing the energy absorbing capacity of these waste mixtures, a better understanding of 56 the effect that RC has on the geotechnical behavior of SFS+CW+RC mixtures from a 57 mathematical perspective is urgently needed. Despite the research already carried out to 58 investigate the behavior of soil-rubber mixtures in the laboratory, only a few focused on the 59 theoretical models used to predict the behavior of soil-rubber mixtures.60Stress-dilatancy is a fundamental aspect needed to model the stress-strain behavior of soil. It 61 has been suggested that dilatancy in its initial form is a unique function with the stress ratio ߟ 62 ...

Railway tracks are conventionally built on compacted ballast and structural fill layers placed above the natural (subgrade) foundation. However, during train operations, track deteriorations occur progressively due to ballast degradation. The associated track deformation is usually accompanied by a reduction in both load bearing capacity and drainage, apart from imposing frequent track maintenance. Suitable ground improvement techniques involving plastic inclusions (e.g., geogrids) and energy absorbing materials (e.g., rubber products) to enhance the stability and longevity of tracks have become increasingly popular. This paper presents the outcomes from innovative research and development measures into the use of plastic and rubber elements in rail tracks undertaken at the University of Wollongong, Australia, over the past twenty years. The results obtained from laboratory tests, mathematical modelling and numerical modelling reveal that track performance can be improved significantly by using geogrid and energy absorbing rubber products (e.g., rubber crumbs, waste tire-cell and rubber mats). Test results show that the addition of rubber materials can efficiently improve the energy absorption of the structural layer and also reduce ballast breakage. Furthermore, by incorporating the work input parameters, the energy absorbing property of the newly developed synthetic capping layer is captured by correct modelling of dilatancy. In addition, the laboratory behavior of tire cells and geogrids has been validated by numerical modelling (i.e., Finite Element Modelling-FEM, Discrete Element—DEM), and a coupled DEM-FEM modelling approach is also introduced to simulate ballast deformation.

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