Worldwide, flexible pavements are the paramount type of pavements. These national assets can be recycled to serve the next design life without the need to dispose of them in landfill. The old/distressed, flexible pavement material is called, reclaimed asphalt pavement (RAP) material. In view of the sustainable development practice, 100% RAP should be recycled. However, the practical range of RAP incorporation in a drum mix plant ranges from 10% to 50% whereas in a batch mix plant, it is 10%–35%. In a batch mix plant, incorporation of the hot dried RAP (instead of cold RAP feeding) can increase the RAP incorporation level by 20%. Studies recommended that the rejuvenator should be added over the RAP material instead adding with the base binder. The addition of rejuvenator on the RAP conveyor belt (to the pug mill), provided sufficient time for rejuvenating the aged binder coating over RAP aggregates. Further, a thorough knowledge of the mix design process of recycled hot mix asphalt (RAP-HMA) is essential to produce a durable mix. For high RAP content (>20%), the RAP binder properties are important for the mix design process. However, very limited studies discussed (in detail) the recovery process of the RAP binder. The review article through light on the binder recovery process, method of RAP gradation, specific gravity determination for RAP material, minimum desirable properties of the RAP material etc. This review paper also provides a narrative review of the historical development of RAP-HMA technology, technical aspects related to the procurement of RAP material, mix design and production of the recycled mix. Moreover, the international & national policies/laws for construction and demolition waste are discussed. 

Mix design, development, production and policies of recycled hot mix asphalt: A review

This study investigated the properties of asphalt mixtures, including recycled asphalt pavement, at high ratios. In addition, to improve the properties of asphalt mixtures containing recycled asphalt pavement, bitumen was modified with a rejuvenator at proportions of 2, 4, and 6% and used together with 35, 40, and 45% recycled asphalt pavement. Based on test results, the strength of asphalt mixtures increased as the ratio of recycled asphalt pavement added to asphalt mixtures increased. In addition, all combinations of recycled asphalt pavement and rejuvenator agent had higher indirect tensile strength values according to the reference mixture. The rutting resistance of asphalt mixtures increased as the ratio of recycled asphalt pavement added to the asphalt mixtures increased. Asphalt mixtures containing 45% recycled asphalt pavement and 2% rejuvenator-modified bitumen showed the best rutting resistance. The significance of the obtained results was determined with appropriate statistical analysis. So, it has been determined that the rejuvenator used in this study can effectively improve the properties of asphalt mixtures containing recycled asphalt pavement. Finally, the rejuvenator agent used in this study allowed the utilization of recycled asphalt at a higher ratio than the amount specified in the Highway Technical Specification. 

Effects of utilization of rejuvenator in asphalt mixtures containing recycled asphalt pavement at high ratios

Approximately 99% of reclaimed asphalt pavement (RAP) has been recycled in Japan in recent years. However, the deterioration in quality of repeatedly recycled RAP cannot be prevented through existing methods, nor can sustainability be guaranteed. In addition, it is challenging to procure virgin aggregate and binder. Therefore, to ensure the quality and supply of future recycled hot-mix asphalt, it is necessary to explore sustainable recycling technologies. This study examined the advantages and disadvantages of the technical approaches to the recycling of RAP into aggregate and binder. We develop a recycling technology (separate recycling technologies) that uses hot water to separate and restore aggregate and binders to their initial condition from RAPs. The quality of the aggregate, recovered by the hot water rubbing method at 80 °C and 90 °C, fully satisfies the standard values for virgin aggregate at all temperatures. The aged binders, reacting through a hydrothermal decomposition method (hydropyrolysis), with a reaction temperature of 300–350 °C and a reaction time of 0–15 min, tend to have a significantly improved effect. These results confirm that both the hydrothermal rubbing and hydropyrolysis methods could be beneficial options for establishing separate recycling technologies for RAP.

/pdf/technical-approaches-to-the-recycling-of-reclaimed-asphalt-10zf66gj.pdf

Technical Approaches to the Recycling of Reclaimed Asphalt Pavement into Aggregate and Binder

Refined separation not only controls the variability of reclaimed asphalt pavement (RAP), but also improves the mixing ratio of RAP and the quality of recycled asphalt mixtures. This study examines RAP treated with various refined separation frequency parameters, analyzes the variation rules and the variability of RAP aggregate gradation, asphalt content, asphalt properties, and aggregate properties, and calculates the maximum mixing percentage of coarse RAP material by using the gradation variability control method and the asphalt content variability control method. The results show that the variability of gradation and asphalt content of coarsely separated RAP is considerable, and a refined separation process significantly reduces the variability of gradation and asphalt content of RAP; the agglomeration of RAP decreases with an increase in the refined separation frequency; and the RAP agglomeration of three kinds of RAPs (E1, E2, and E3) under a refined separation frequency of 55 Hz reduces by 6.40%, 4.30%, and 4.30%, respectively, as compared with that of coarsely separated RAPs. The asphalt content of the refined separation RAP gradually decreases with an increase in frequency, and the asphalt content of E1 and E2 (55 Hz) was only 0.95% and 1.10%, respectively. The maximum percentage of RAP in recycled asphalt mixtures was calculated using the gradation variability control method and the asphalt content variability control method, respectively. The maximum proportions of RAP were 45% and 33% for A1 (0 Hz), respectively, and the maximum proportions of RAP for E1 (55 Hz) were all 100%. The results of the two methods show that the process of refined separation can increase the maximum proportion of blended RAP materials. They also demonstrate that the refined separation process can increase the maximum blending ratio of coarse RAP materials, thereby improving the quality of the RAP, increasing the proportion of RAP blending, and ensuring the quality of the recycled asphalt mixture. In conclusion, the refined separation process holds promise for maximizing the potential value of RAP and optimizing its recycling, environmental, and economic benefits. 

The Effect of Refined Separation on the Properties of Reclaimed Asphalt Pavement Materials

Most road surfaces globally are constructed using bituminous materials. The construction of new roads and the maintenance of existing ones demand a huge amount of virgin natural aggregates. Depletion of resources that takes place during the construction of the road has an impact on cost and also on the environment. Hence, there is a need to reduce virgin aggregate use for bituminous pavement construction. This can be achieved by utilizing sustainable materials such as marble waste and reclaimed asphalt pavement (RAP) in hot mix asphalt (HMA)-type road construction. This research work is focused on sustainable development goal (SDG) 12, exclusively on the target number 12.5 which describes the recycling and reuse of materials. However, no investigations were seen to be reported on the integrated utilization of sustainable materials and RAP in bituminous paver blocks. The bituminous mixes were evaluated based on strength and compared with the control mix in this study. Bituminous paver blocks were then cast using sustainable materials and tested in the laboratory to assess the performance of the blocks through a compression test, Cantabro loss test, and wheel rut test. The test results gave satisfactory values; hence, these bituminous blocks can be used for service maintenance of the pavement structures. The study indicates that using sustainable material along with RAP in blocks can provide an eco-friendly, easily maintainable pavement system which makes it a key approach to SDG 9 as well, in terms of innovative infrastructure solutions. 

/pdf/development-and-evaluation-of-sustainable-bituminous-paver-3telnu78.pdf

Development and Evaluation of Sustainable Bituminous Paver Blocks

A series of laboratory tests were conducted to confirm the aging property of repetitive recycled asphalt and mixture. In this study, rejuvenator which consists of different component, and high penetration asphalt were applied to recycling procedure. As a result, the differences of the aging were occurred in physical and chemical properties of recycled asphalt mixture and recycled asphalt, according to difference in composition of rejuvenator. The rejuvenator, which composed of low saturates and high aromatics could constrain the aging of properties in recycled asphalt mixture and recycled asphalt. 組成の異なる再生用添加剤と針入度の大きな石油アスファルトを用いて，繰り返し再生したアスファルト混合物およびアスファルトの性状の変化を検討した．その結果，再生用添加剤などの組成の違いによって再生アスファルト混合物の工学的性状や再生アスファルトの物理的，化学的性状に変化の程度に差が見られ，飽和分が少なく芳香族分の多いものを用いた場合に再生アスファルト混合物や再生アスファルトの性状の変化が少ないことがわかった．

/pdf/the-effect-of-chemical-component-in-rejuvenator-on-the-14fur6kjps.pdf

The effect of chemical component in rejuvenator on the properties of repetitive recycled asphalt and mixture

A basic study on the separation recycling technology of reclaimed asphalt pavement

Recently drainage pavement has been more widely used as a high-performance pavement offering both safety and comfort, for applications ranging from highways to general roads. However, there have been reports of cases in which drainage pavement's characteristic structure of allowing rainwater to flow inside the body of the pavement has given rise to damages (such as the rutting) within a short period of time, and it shows that the stripping resistance of the asphalt mixture is thus an important indicator for drainage pavement maintenance. Stripping resistance is evaluated through pressurized water permeation-method stripping acceleration tests and modified Lottman tests, but these are problematic in that they are time-consuming and entail complicated procedures. The authors have attempted the development of a pressurized hot water-method stripping acceleration test by focusing on the asphalt stripping effect of pressurized hot water. As a result, they verified that asphalt mixture stripping resistance can be evaluated more conveniently and efficiently by a hot-water-method test. 近年，排水性舗装は，安全性や快適性を付与する高機能舗装として，高速道路から一般道路まで広く普及している．しかしながら，排水性舗装は，雨水を舗装体内で排水する特徴的な構造から，わだち掘れ等の破損が短期間で生じる事例が報告されており，アスファルト混合物の剥離抵抗性は，排水性舗装の維持管理において，重要な指標と言える．現在，アスファルト混合物の剥離抵抗性は，加圧透水式剥離促進試験や修正ロットマン試験によって評価されているが，これらの試験には，長時間を要する，または手順が複雑といった問題がある．著者らは，加圧熱水のアスファルト剥離効果に着目し，加圧熱水式剥離促進試験の開発を試みた．この結果，熱水式試験によって，簡便かつ効率的にアスファルト混合物の剥離抵抗性を評価できることを確認した．

Development of pressurized hot water stripping resistance evaluation test for asphalt mixture

近年，アスファルト舗装発生材の持続的な循環利用技術の開発は急務となっており，様々な研究がおこなわれている．著者らは，高温高圧水の有する有機物への溶媒性能および分解性能に着目し，350°Cの高温高圧水を用いた水熱分解法による劣化アスファルトの性状回復技術の開発を行っている．本研究では，水熱分解法の劣化と再生を複数回繰返した劣化アスファルトへの適応性を確認した．その結果，水熱分解法により回復したアスファルトは，従来の再生方法と比較して伸度の回復が大きく，高分子成分が減少することを明らかにした．また，水熱分解後のアスファルトを配合したアスファルト混合物は再生加熱アスファルト混合物の圧裂係数による品質目標値を満足すること明らかにした． 

Adaptability of hydrothermal decomposition method fwor repeated recycling of reclaimed asphalt pavement

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