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.

Recycling or, in other words, reuse of pavement is one of the latest technologies in the field of road construction that is now more accepted than other pavement construction methods. In addition to better environmental protection, this technology results in significant cost savings. Still, one of the major concerns of its use is the creation of undesirable properties in asphalt mix, such as bitumen aging and reduced cracking resistance. The use of rejuvenation agent and WMA (warm mix asphalt) additive are the solutions to improve the performance of asphalt mixers containing RAP (reclaimed asphalt pavement) materials. Hence, in this research, in order to evaluate the effect of using RAP on the fracture resistance of WMA mixtures, the RAP materials with two dosages of 25% and 50%, one type of rejuvenation agent and Sasobit, as a WMA additive, were employed. To study the fracture resistance of the mixtures at the temperatures of -15 °C and 25 °C under mode I loading, semi-circular bending test was selected, and different fracture parameters including critical fracture load, fracture energy, flexibility index, cracking resistance index and fracture toughness were calculated. The results exhibited that the addition of RAP material to the mixture had a negative effect on the fracture parameters at different temperatures and resulted in the reduction of these parameters. While the mixtures containing rejuvenator showed more elastic behavior than those without rejuvenator. Therefore, the use of a rejuvenator led to the improvement of the fracture parameters.

The use of recycled asphalt pavement (RAP) has been one of the available solutions in road maintenance due to cost reduction and preservation of natural resources. On the other hand,by using RAP materials, aged binder in the RAP causes improper performance of the asphalt mixture, including reducing the cracking resistance. Nowadays, rejuvenators are used to improve the performance of asphalt mixtures containing RAP. Iran is one of the active countries in rice cultivation, while 70% of rice bran is unused. This study investigated rice bran oil as a rejuvenator in asphalt mixtures containing 20%, 30%, and 40% RAP materials by dynamic creep test, resilient modulus test, and semicircular bending (SCB) test. The results show that using rice bran oil in asphalt mixtures as a rejuvenator causes a decrease in the flow number, resilient modulus, and fracture toughness values by an average of 31%, 27%, and 13%, respectively, also increase in fracture energy values by an average of 24%. The results show that using rice bran oil improves the performance of asphalt mixtures containing RAP by reducing the viscosity of aged binder in RAP. As a result, implying rice bran oil as a rejuvenator in asphalt mixture due to the using rice waste and low cost and environmentally friendly, can be a good way to enhance asphalt pavement performance.

In this study the effects of short and long term ageing on some of engineering properties of recycled asphalt concrete containing high percentage of reclaimed asphalt pavement (RAP) and rejuvenated by different dosages of waste engine oil (WEO) have been investigated. The coarse fraction of asphalt concrete has been replaced with RAP and the mixture has been rejuvenated by different dosages, namely 0, 4, 7 and 10% (by the weight of total binder) of WEO, and the volumetric and Marshall properties, indirect tensile strength (ITS) and creep properties of the mixtures after experiencing different ageing conditions including un-aged, short term and long term ageing have been evaluated. Results reveal that inclusion of RAP into mixture increases the optimum binder content, Marshall stability and quotient, ITS and creep resistance, the Marshall stability and quotient, optimum binder content, ITS and creep resistance decreases with increasing WEO content. In un-aged condition, Marshall stability and quotient increase up to 7% of WEO content, beyond which the trend reverses. Also, ageing results in increase of Marshall stability, ITS and creep resistance, and decrease of flow with more effect after long term ageing. The degree of ageing effect on the properties depends on the type of ageing, type of mixture and amount of rejuvenator. The effect of ageing on Marshall quotient increases up to 7% of WEO content, beyond which decreases. For ITS the effect of ageing decreases with increase of WEO content, and for creep resistance, the effect of ageing increases with increase of WEO content. The Marshall stability and ITS are more affected by ageing in recycled mixtures than in control mixture and the level effect decreases with increase of WEO. Furthermore, results reveal that creep resistance is more affected from ageing than the ITS and Marshall properties.

Fatigue cracks are considered as one of the most significant pavement failures. The cause of fatigue cracks is the changes in environmental temperature conditions and repeated loading of vehicles. Additives can enhance the tensile strength of asphalt pavement layers and increase their life. In this article, through laboratory studies, the effect of using a rejuvenator as an additive in asphalt mixture, called “Rapiol”, on improving the fatigue performance of both unaged and aged asphalt pavements was investigated. To achieve this, the study utilized the Linear Amplitude Sweep (LAS) test at strain levels of 2.5% and 5%, and the Four-Point Bending Beam (4-PBB) test in strain-control mode (at strain levels of 400, 600, and 800 microstrains). The LAS test results indicate that in unaged conditions, the Rapiol rejuvenator improved fatigue life by 7.5% and 3% at strain levels of 2.5% and 5%, respectively. However, in aged samples, fatigue life increased by 4.1% at 2.5% strain but decreased by 21.8% at 5% strain. Moreover, according to the 4-PBB test results, using Rapiol in unaged asphalt mixture samples enhanced fatigue life by 42% and 284% at 400 and 800 microstrains, respectively. Similarly, in aged asphalt mixture samples, fatigue life increased by 100% and 500% at 400 and 800 microstrains, respectively.

One of the main factors that cause distresses and cracks in asphalt pavement is ageing and it makes pavements deteriote over time. Previous studies about this phenomenon have shown that the use of "bioasphalt" has a positive effect on the ageing and it can act as an antioxidant and rejuvenating material. In this study, the possibility of using lignin and waste engine oil in bitumen to improve the chemical and ageing properties of bitumen was investigated. The lignin used in the study was extracted from black liquor. Waste engine oil was taken from a car repair shop. The samples are PG64-22 as control sample, samples containing 5 and 10% lignin, samples containing 4% waste engine oil, and samples containing both additives. FTIR analysis, ICP analysis, CHNS analysis and SEM analysis were performed on the samples to better investigate the effect of additives on aging. Also, three important aging indices were calculated using RV, DSR and FTIR tests. The results showed that the addition of lignin or WEO or a combination of both, can improve the chemical properties of bitumen. Also using waste materials in bitumen can be useful from an environmental and economic point of view. They are also effective for aging resistance and can be used as a rejuvenator.

In asphalt pavement hot recycling, reclaimed asphalt pavements called "RAP" and aged bitumen extracted from them are known as reclaimed asphalt binder (RAB). In this study, the performance of RAB-containing binder compounds with different percentages of recycled bitumen (0, 25%and 50%) and RAP-containing asphalt mixtures with varying contents of the RAP (0, 25% and 50%) were compared in two conditions (with and without a rejuvenating agent). The main purpose of this study was to evaluate the relationship between bitumen’, s performance parameters and asphalt mixture’, s performance parameters. Therefore, the correlation between the parameters obtained from the fatigue and the rutting tests of binder compounds (linear amplitude sweep test and multiple stress creep and recovery test, respectively) and parameters obtained from the fatigue and rutting tests of asphalt mixtures (four-point beam fatigue test and dynamic creep test, respectively) were investigated for the first time in RAP-containing asphalt mixtures. The results indicated that the behavior of asphalt mixtures in fatigue and rutting resistance was agreed with the behavior of the binder compounds in the linear amplitude sweep and multiple stress creep and recovery tests. Besides, there were statistically good correlations between the binder's fatigue life and asphalt mixtures' fatigue life and relatively good statistical correlations between binder's rutting resistance and asphalt mixtures' rutting resistance in the RAP-containing asphalt mixtures.

Properties of asphalt mixture change with time. These changes directly affect operation of the asphalt mixture. This issue makes the road maintenance important. One of the methods of road maintenance for preventing deeper problems is using rejuvenator materials in improving the rheological and mechanical properties of the aged tar; thus, the pavement will not contront different cracks and future failures will be prevented. The main purpose of this study was to prove the effect of rejuvenator materials on asphalt mixture ageing, specialy in field cases and in situ application. Four compounds were made as rejuvenator and were sprayed over the pavement. After removing a 1. 5 cm layer from top of the sample, the corresponding tar was extracted and DSR, penetration value and softening point tests, before and after applying the rejuvenator materials, were carried out. Since the friction of rejuvenated surface is an important issue for road specialists, British pendulum test was also performed in order to make sure about friction of pavement surface for reopening. Results showed that in penetration value, DSR and softening point tests, all of the 4 compounds rehabiliated the properties of asphalt mixture and their differences were not significant. Results of British pendulum test showed proper performance of the rejuvenating materials, for surface friction of the pavement, after being applied.

Nowadays, to solve environmental problems and crises, the concepts of circular economy and sustainability have been paid more attention and extensive efforts are being made to recycle or reuse non-renewable resources. In the field of road pavement engineering, encouraging the use of recycled asphalt pavements is one of the easiest ways to promote a circular economy. One of the main issues regarding the use of this recycled material is the aged bitumen which it’s aging and rejuvenation process affect significantly on the durability and service life of asphalt pavements. Therefore, achieving complete knowledge of these aspects from a chemical and rheological point of view is essential. In this research, while studying the aging process, by introducing different methods of aged bitumen reclaiming, the types of biological and oil-derived rejuvenators studied in different researches have been introduced and their performance has been reviewed. Also, different chemical analyses were introduced and described as tools to investigate bitumen aging and rejuvenation processes. Finally, in order to rejuvenate the aged bitumen of recycled asphalt pavements and choose the type, dose and method of adding rejuvenators, it is recommended that the optimal dose of rejuvenator is determined based on long-term field performance data and in full-scale applications. It is also recommended to investigate the effect of rejuvenating chemical components on the characteristics of rejuvenated bitumen, perform field performance studies of rejuvenated asphalt pavements, and the possibility of combining the rejuvenating effect of recycled agent with other modifiers to improve asphalt performance in specific climatic conditions.

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.