جستجوی مقالات مرتبط با کلیدواژه "recycled asphalt" در نشریات گروه "عمران"

Many researchers have shown that using rejuvenators and polymer-modified bitumen can improve the performance of recycled asphalt mixtures against cracking, fatigue, and rutting. Nevertheless, limited research has been performed on modified rejuvenators with polymer, and there are many obscurities on the performance of these rejuvenators on the behavior of the recycled asphalt mixture. Therefore, in this research, the performance of 25%, 50%, and 75% RAP mixtures containing polymer rejuvenator (i.e., nanopoly, Tiss, and crumb rubber modified waste cooking oil (MWCO)) and vacuum bottom have been studied, and the results were compared together. For this purpose, after obtaining the optimal percentage of each rejuvenator and performing the mix design formula tests, the dynamic creep test, moisture sensitivity test, and semi-circular bending test were conducted. The results show that the modification of rejuvenators with polymer improves the rutting resistance of mixtures. Also, the mixtures containing nanopoly and Tiss, despite the weaker initial cracking resistance, have a better performance against the growth of the crack. Furthermore, the mixtures containing tiss and nanopoly showed a good performance against moisture sensitivity. The mixtures containing MWCO did not perform well against cracking and moisture sensitivity.

In recent years, due to the high costs of pavement construction and environmental considerations, various recycled materials have been used in the roller compacted concrete pavements. On the other hand, due to the increase in the price of bitumen in flexible pavements, the use of roller concrete in the construction of pavements seems to be more economical. In this research, the mechanical properties, abrasion resistance and impact resistance of rolled compacted concrete containing recycled asphalt and fly ash have been investigated. A total of 15 mixture design were studied with replacement amounts of 10%, 20% and 30% of fly ash as a substitute for cement and 5%, 10% and 15% of fine-grained recycled asphalt as a substitute for aggregate. In order to determine the optimal amount of fly ash, first, compressive and bending strength tests were performed on 7-day samples containing 10%, 20% and 30% of fly ash, and the optimal percentage was obtained. Therefore, in mixtures 4 to 6, the amount of fly ash to replace cement for all mixtures was considered the optimal value (10%). It should be noted that for more accuracy, the 28-day samples containing different amounts of fly ash were also examined. Results of this research showed that the use of fine-grained recycled materials at the rate of 5%, 10% and 15% along with 10% of fly ash led to an increase in compressive strength by 20%, 12% and 4%, bending strength by an average of 10% and tensile strength on the average is about 40% compared to control sample. However, all samples containing recycled asphalt have shown a significant decrease in abrasion resistance.

Recycling and reusing materials have received much attention from researchers in recent decades. Today, environmental issues have become very important due to the limitation of available resources as well as the increase in the cost of new materials. Since most of the existing roads in Iran have flexible pavements, using reclaimed asphalt pavement (RAP) and using fewer new materials can be considered an environmentally friendly solution. In recycling asphalt pavements, there is a major concern related to low-temperature cracking. The purpose of this research is to investigate the low-temperature cracking properties of asphalt mixtures containing RAP along with other additives to introduce a mixture with performance characteristics equivalent to the new asphalt mixture. For this purpose, asphalt mixtures with two different contents of RAP (25% and 50%) were considered. Also, to improve their adhesion properties, the addition of a rejuvenator (10% by weight of RAP binder as the optimal percentage) and to improve the resistance of the mixture against cracking, crumb rubber (10% by weight of new binder) was considered. An indirect tensile strength test and a semi-circular bending test (SCB) were performed to investigate the properties of the mixtures. Also, the crack mouth opening displacement (CMOD) during the SCB test was measured through imaging. According to the SCB test, adding RAP to the base sample reduces the fracture energy. But adding rejuvenator and crumb rubber to the recycled samples improves the properties of the mixture against crack growth. The results showed that the asphalt mixtures containing RAP and additives, according to the tests used in this research, presented equal or even better performance than the new asphalt mixture. Also, the combined index of fracture energy - CMOD can be used as a suitable criterion to investigate the effect of RAP, rejuvenator and crumb rubber in asphalt mixture.

In this research, using asphalt decomposition test based on AASHTO-T164 standard, it is investigated how burnt oil and asphalt chips affect the properties of hot asphalt. In this study, burnt oil with different percentages was added to the worn bitumen which was extracted from the worn asphalt by extraction method and was subjected to penetration degree and softening point tests. The addition of rejuvenator increases the Marshall resistance's cause is to provide the necessary adhesion and cohesion between the aggregate and bitumen, but with the addition of a percentage of rejuvenator and increasing the penetration of bitumen, the adhesion and cohesion of bitumen and aggregates is reduced. This will reduce the durability of the samples, which is reduced with 20% of burnt bitumen oil and used in the asphalt mixture resulting from the mixing of asphalt chips and new materials. It is recommended to use 50% of asphalt chips to improve the physical properties of the mixture. . The results show the effect of burnt oil as a rejuvenator for worn bitumen and with increasing the percentage of rejuvenating material, the parameters of worn bitumen also improve and also with increasing percentage of asphalt chips (RAP) in samples without Addition of new bitumen has been made, strength and durability have also increased and consequently the Marshall ratio has also increased.

The recent increase in bitumen prices and environmental considerations has expanded the use of recycled asphalt mixtures. These mixtures are prepared with different percentages of recycled and new materials including bitumen and aggregate. Sometimes it is necessary to examine the effect of different laboratory parameters quickly and with a smaller number of samples. In this paper, the Taguchi method with 3 effective factors including the percentage of recycled materials (in three levels of 0, 25 and 50%), type of recycled materials (in two levels of two different sources) and the percentage of bitumen (in 3 levels of 4, 5 and 6%) was used to design experiments for rapid analysis of laboratory samples. The strength and volumetric characteristics of asphalt mixtures were determined and analyzed using Minitab software in L18 orthogonal array. The effect of each of the input parameters on the obtained results was determined by signal-to-noise ratio and analysis of variance. The results showed that the percentage of recycled materials significantly affects the strength and volumetric behavior of recycled mixtures. Contrary to expectations, the effect of the source of recycled materials is less than other input parameters.

Enormous amounts of waste materials generated from the demolition of buildings and pavements have created problems for the environment. In this research, various percentages of base material made of natural aggregate have been replaced with recycled concrete and asphalt that has been crushed and graded, and some physical and engineering properties have been studied. Physical properties such as density and water absorption, cleanliness, hardness and resistance to abrasion and performance properties including compaction characteristics, load-bearing capacity (CBR) and hydraulic conductivity have been evaluated. The results show that, in terms of the criteria specified in specifications for base materials, the mixtures containing recycled aggregates are weaker; however, but most of them satisfy the requirements of specification to be used as highway pavement base layer. In terms of load-bearing capacity defined by CBR, all the mixtures containing recycled concrete aggregates satisfy the minimum requirement of 80% for CBR, but some of the mixtures containing recycled asphalt concrete aggregate do not satisfy the CBR requirement. The results of permeability test show that the permeability increases with increasing recycled asphalt replacement, and decreases with increasing recycled concrete replacement. In addition, highest increase of permeability is obtained by replacing the fine fraction of natural aggregate with recycled asphalt, and the lowest permeability is obtained by replacing the fine fraction of natural aggregate with recycled concrete aggregate (11 times lower than the control mixture). Crease in permeability (an increase of about 5 times) and fine-grained concrete placement caused the largest decrease in permeability.

One of the major problems caused by construction and demolition of buildings and highways is the environmental pollution due to the produced waste materials. Therefore، in addition to the protection of environment، the recycling and reusing of the waste materials is an economical measure. One of the applications of the waste materials is for highway construction. In order to investigate the applicability of the waste materials in pavement structure، as base or subbase layer، in this research، the compaction and mechanical properties of recycled asphalt and concrete stabilized by cement and reinforced by steel fibers have been studied. Different combinations of the recycled concrete and asphalt have been stabilized by various cement and steel fiber contents، and the compaction properties and the compressive and bending strength have been investigated. The results show that، in all the combinations، the optimum moisture content and the maximum dry density increase with increasing the cement content. In addition، it is found that، up to 9% of cement content، the compressive strength increases with increasing the cement content، and beyond that، the compressive strength decreases with increasing the cement content. Also، the compressive strength of the mixtures increases by addition of steel fiber، with the highest compressive strength at 1% of fiber content. The results also show that، the bending strength of the mixtures increases by increasing the cement and steel fiber content.