دانلود رایگان مقاله انگلیسی خواص خستگی مخلوط آسفالت لاستیک خرد شده مورد استفاده در راه آهن - الزویر 2018

abstract

The use of asphalt mixtures in railway tracks provides a positive contribution to the bearing capacity, stability, durability and more importantly damping properties of the railway structure particularly for the new generation of low-vibration-railway track systems. However, one of the main concerns in the use of asphalt mixtures in railways is their fatigue cracking caused by the repeated traffic loading. The present study focused on the fatigue damage behavior of asphalt mixtures in the railways through using the viscoelastic continuum damage theory. Three experiments of creep compliance, constant crosshead rate and cyclic fatigue tests were carried out on some asphalt mixtures with different air void contents and aging conditions. Based on the results obtained, the crumb rubber modification of railways asphalt mixtures at low stress levels increases the fatigue life of asphalt up to 7.2 times while this increase is at the most 3.6 for the highway asphalt mixture. Furthermore, reducing the air void content from 4% to 2% for the crumb rubber modified asphalt mixture increases the fatigue life by 9.4 times at high stress levels and 18.2 times at low stress levels, which is a great improvement. It was shown that the lowest fatigue life is obtained in the aged crumb rubber modified mixture (i.e., 20 percent of unmodified asphalt mixture).

Summary and conclusions

The viscoelastic continuum damage theory was used in this research to interpret the fatigue properties of asphalt mixtures. Crumb rubber modified asphalt mixtures were prepared in two different air void contents to investigate the mechanical behavior of the railway asphalt mixtures and compare them with the regular road pavements asphalt mixtures. An unmodified mixture was also used to evaluate the effectiveness of the CR modification, and an aged mixture was utilized to evaluate the fatigue performance of the aged asphalt mixtures in the railway applications. The creep compliance test was carried out to investigate the linear viscoelastic behavior of asphalt mixtures. Two different loading forms of constant crosshead rate (or monotonic) test and the constant crosshead cyclic test were utilized to drive the damageinduced properties of the asphalt samples. The strain rate dependency of the mixtures during the monotonic test, when the damage was negligible, was shown to be correctly eliminated using the ‘‘correspondence principle” and the introduction of pseudostrain concept. The damage characteristic curves for an individual material were shown to be unique independent of the loading type or the rate of loading and hence the viscoelastic continuum damage theory was shown to precisely work for these materials; and the testing errors among different samples were shown to be negligible. A model function was fitted to the characteristic curves of the mixtures and the obtained curves were compared.