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Impact loads generated from the dynamic effect of passing trains can exacerbate the degradation level of ballast aggregate of railway track. To diminish the induced impact loads, the use of crumb rubber (CR) in the ballast course is characterized as a well-established procedure related to the modification of utilized material. Nonetheless, more in-depth assessments of size and percentage of CR particles combined with ballast aggregate are still required. The present study evaluates the influence of size and content of CR particles used for degradation reduction of ballast aggregate subjected to impact loading. For this purpose, a large-scale impact loading test is carried out on prepared specimens of aggregate by considering the initial gradation, subgrade condition, as well as the size and content of CR particles. The results indicate less ballast degradation for a higher percentage of CR particles. Meanwhile, the enhancement of rubber modified ballast against deterioration is further highlighted in the case of rigid subgrade. In addition, incorporation of larger-sized CR particles (12.5-25 mm) in a ballast specimen comprising more uniform gradation of aggregate can more effectively diminish the amount of degradation. Nevertheless, using smaller-sized CR particles (4.75-9.5 mm) for a ballast sample consisting of a broader range of sizes can better improve resistance against degradation. Key words: railway ballast, degradation, impact loading, crumb rubber, size range. Les charges dynamiques d'impact produites par le passage des trains peuvent exacerber le niveau de degradation des agregats de ballast de la voie ferree. Afin de diminuer les charges dynamiques induites, l'utilisation de caoutchouc granulaire (CR) dans la couche de ballast est une procedure bien etablie liee a la modification du materiau utilise. Toutefois, des etudes plus approfondies sur la taille et le pourcentage de particules de CR combinees a des agregats de ballast sont encore necessaires. Dans le cadre de la presente etude, on evalue l'influence de la taille et du contenu des particules de CR utilisees sur la reduction de la degradation des agregats de ballast exposes a une charge dynamique. Pour ce faire, l'essai de charge dynamique a grande echelle est realise aupres d'echantillons d'agregats prepares en prenant en compte la gradation initiale, l'etat du sol ainsi que la taille et la teneur des particules de CR. Il en resulte une diminution de la degradation du ballast pour un pourcentage plus eleve de particules de CR. Parallelement, l'amelioration du ballast modifie au caoutchouc contre la deterioration est encore mise en evidence dans le cas d'un sol de fondation rigide. En outre, l'incorporation de particules de CR de plus grande taille (12,5-25 mm) dans un echantillon de ballast compose d'une gradation plus uniforme de l'agregat peut diminuer plus efficacement le degre de degradation. Cependant, en utilisant des particules CR de plus petite taille (4,75-9,5 mm) pour un echantillon de ballast constitue d'une gamme plus large de tailles, on peut ameliorer la resistance a la degradation. [Traduit par la Redaction] Mots-cles: ballast des voies ferrees, degradation, charge dynamique, caoutchouc granulaire, gamme de taille., 1. Introduction A ballast course consisting of coarse-grained aggregate acts as a crucial structural layer of ballasted railway tracks. Boosting the drainage of water from the track structure as well [...]

Fatigue cracking is a significant cause of failure in flexible pavements at moderate temperatures. Neat bitumen cannot properly perform at all temperatures and environmental conditions due to the increasing traffic volume. Consequently, this study examined the simultaneous usage of carbon nanotubes (CNTs) and the styrene-ethylene/propylene-styrene (SEPS) polymer as bitumen modifiers. The linear amplitude sweep (LAS) test and surface free energy (SFE) theory were used to determine the rheological characteristics and thermodynamic parameters of neat and modified bitumens, respectively. Using the SEPS nanocomposite up to 6% increased the fatigue life and moisture damage resistance of the asphalt mixtures by improving thermodynamic parameters such as adhesive free energy in dry and wet conditions. According to the LAS results, the modified bitumen outperformed the neat bitumen in terms of fatigue life under different strain levels. The fatigue life of the asphalt mixtures also decreased as the temperature increased from 10 to 20°C. However, for the mixtures containing the SEPS nanocomposite, the reduction in fatigue life was less noticeable due to the lower temperature sensitivity of the modified bitumen. The mixtures containing 6% SEPS nanocomposite demonstrated the highest performance. [ABSTRACT FROM AUTHOR]

Coarse recycled concrete aggregates (CRCAs) were used as substitutes in asphalt mixtures. These aggregates have a layer of porous cement mortar on their surfaces that impairs their physical and mechanical properties. Therefore, their surfaces were coated with waste plastic bottles to improve their quality. Fatigue cracking, as a critical failure, in asphalt mixtures containing 0, 15, 30, and 50% coarse recycled concrete aggregate was evaluated using the indirect tensile fatigue test in wet and dry conditions. Also, the adhesion of mixture ingredients (bitumen and aggregates) to each other was determined using the sessile drop test based on the surface free energy concept. According to the results, the asphalt mixes containing CRCA had a higher optimum bitumen content compared to the control mixture. The modified asphalt mixtures had a shorter fatigue life in wet and dry conditions. Furthermore, moisture reduced the fatigue resistance of the control and modified asphalt mixtures, and this rate of decline was greater in the mixtures containing CRCA due to their high absorption. [ABSTRACT FROM AUTHOR]

Contamination of railway ballast can influence the permeability of ballast course and consequently the drainage potential of the track substructure. The present study elaborates the water level of the contaminated ballast with sandy material by establishment of laboratory test as well as analytical-numerical method. For this goal, the large-scale permeability tester is utilised to determine the hydraulic conductivity of ballast aggregate fouled with disparate ratios of sandy material. Then, the developed analytical-numerical procedure is applied to predict the elevation of water in the ballast course for considered conditions of boundary of ballast layer as well as specified values of rainfall rate. Based on the obtained results, the permeability of extremely contaminated ballast with sand is nevertheless appropriate. However, the estimated water level of the ballast course is drastically influenced by further contamination of railway ballast layer especially under higher rainfall rates. Meanwhile, the increment of water level on two sides of the ballast course eventuates in more uniform water table along the cross-section of the course which results in more saturation of track substructure. [ABSTRACT FROM AUTHOR]

The performance of the railway track structure is highly affected by degradation of the ballast aggregate in which breakage and abrasion of coarse angular particles result in production of fine grains. Maintenance activities including ballast cleaning and tamping operation can intensify ballast degradation during service life. In addition, initial gradation of ballast aggregate can influence the level of ballast degradation. The main purpose of the present study is to simulate the effect of rearrangement of aggregate during maintenance activities on the degradation of ballast by evaluating the influence of initial gradation of aggregate and rock type. For this purpose, a series of lab-scale compression tests with multiple-step loading are conducted during which ballast particles are taken out from the mould after each step and remoulded before the next step. According to the obtained results, multiple-step loading compression test results in more degradation as well as more axial strain of aggregate samples. In addition, gradation comprised of broad range of ballast particles leads to less degradation of ballast under applied loads. Furthermore, less degradation of ballast particles subjected to compressive loads results in lower axial strains in the specimens. [ABSTRACT FROM AUTHOR]