Eﬀects of crumb rubber content and curing time on the properties of asphalt concrete and stone mastic asphalt using dry process
|نوع نگارش مقاله||
scopus – master journals – JCR
۴٫۲۷۶ در سال ۲۰۲۰
۲۶ در سال ۲۰۲۱
۰٫۹۰۱ در سال ۲۰۲۰
|شاخص Quartile (چارک)||
Q1 در سال ۲۰۲۰
خرید محصول توسط کلیه کارت های شتاب امکان پذیر است و بلافاصله پس از خرید، لینک دانلود محصول در اختیار شما قرار خواهد گرفت و هر گونه فروش در سایت های دیگر قابل پیگیری خواهد بود.
فهرست مطالب مقاله:
Along with the rapid increase in the number of road vehicles, a large amount of waste tires have been created, causing negative eﬀects to the environment. Many attempts have been made to eﬀectively reduce this type of solid waste including the reuse of recycled rubber powder from waste tires as an additive for improving the performance of asphalt mixtures. In this work, the authors aim to study the eﬀects of crumb rubber (CR) on the mechanical properties, especially the rutting resistance, of CR modiﬁed asphalt concrete (AC) and stone mastic asphalt (SMA) by varying two factors-namely, the content of additive and the curing time. The dimension of used CR ranges from 0 to 2.36 mm, which is not too coarse for promoting the CR–bitumen interaction and not too ﬁne for facilitating the pro- duction of CR. The content of CR was increased gradually from 0 to 3% to examine the eﬀects of CR content on the engineering prop- erties and determine the optimal content in the mixture. It was observed that the optimal content is 1.5–۲%, while the optimal curing time that contributes to the maximal increase in the mechanical characteristics of both mixtures could not be determined. In the range of 0–۵ h of curing time, the longer the asphalt mixture is maintained at a high temperature, the better the performance of mixture will be. Ageing was found to have inﬂuence on the performance of asphalt mixtures; however, its eﬀects are not as important as those of CR modiﬁcation.
|بخشی از متن مقاله:|
In recent years, along with the rapid development of infrastructure, the number of vehicles is considerably increasing in developing countries. Countries should not only take advantage of these trends to expand their economy but also pay attention to drawbacks that might aﬀect human beings, such as emission, noise pollution and park- ing lot shortages. According to Messenger in 2008, there were more than one billion tires discharged into landﬁlls, and approximately ۴ billion tires had already been stored in stockpiles . The problem is that these countries must immediately reduce the number of used tires eﬀectively and safely because the environment is likely to be harmed before or during treatment processes. Therefore, the idea of reusing waste tires in highway construction is believed to be currently feasible.
The ﬁrst applications of discharged car tires in asphalt concrete occurred in the ۱۹۶۰s, and the methods were named wet process and dry process, corresponding to the method in which CR is added. The wet process was devel- oped by McDonald with the percentage of waste rubber ranging from 5 to 25% by weight in bitumen. CR is added to bitumen to improve the engineering properties of the binder. Speciﬁcally, at high temperatures, light non-polar fractions are absorbed into the polymer networks. As a result, the ﬁnal bitumen becomes harder, and swelling CR particles soften. If the temperature is too high or the time is too long, the swelling will stop and be replaced by depolymerization. This results in the dispersion of rubber into bitumen. These phenomena will occur at temperatures in the range of 160–۲۰۰ C and are time-dependent. How- ever, one of the obstacles that restrict CR modiﬁed asphalt binder from applications is storage stability. Due to the reduced density after swelling, CR modiﬁed particles migrate to the top of the storage container, leading to phase separation [2–۷].
In contrast, the dry process, in which the additive is blended with aggregate before mixing with bitumen, is well known for its environmental beneﬁts. Because the less fuel is consumed the more CR is used . This method was invented and ﬁrst applied in Sweden and thereafter patented in the USA in 1978 with the name of PlusRide . In addition to PlusRide, the following two methods have also applied CR in the dry process: generic dry pro- cess and chunk rubber process. While PlusRide consumes CR with a dimension range of 2–۶٫۳ mm in gap-graded asphalt concrete, the generic dry technology uses 3% of 0.18–۲ mm CR by weight of the mixture. The chunk rubber process uses 3–۱۲% CR with sizes ranging from 4.75 to 9 mm in the mixture. The aggregate gradation used in this process depends on the CR dimensions. This means that the rubber particles will replace the same-sized aggregate particles.
In studies about the dry process, CR is used in hot mix asphalt as a replacement for parts of coarse and ﬁne aggre- gate, resulting in a preference for gap gradations, and aggregate does not appear in the dimensions of the added CR. Furthermore, the work of designing a gradation curve of aggregate corresponding to the added rubber powder is quite complicated because the melting of ﬁne CR particles will occur at high temperatures. For example, the chunk rubber process could consume CR up to 12% by weight of the mixture. The application of CR in hot mix asphalt is a promising solution, but problems of consistency in the characteristics of the mixes should be considered. Moreover, Mujibur Rahman  and Herna´ndez-Olivares et al.  noted that the distance between the mixing plant and construction site has a considerable eﬀect on the con- sistency between mixes; at high temperatures, the interac- tion between the rubber and bitumen continues during transportation.
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