Uses of Reclaimed Asphalt Pavement (RAP) in Flexible Pavements

Abstract

One of the most frequently used waste materials is reclaimed asphalt pavement (RAP). The use of RAP can help reduce the cost of a project and ensure that the project is eco-friendly. Therefore, the aim of this study is to give a detailed description of the production of RAP to ensure that the rehabilitation and maintenance of pavements as well as the construction of pavements are environmentally friendly and cost effective. Previous works have shown the benefits of using RAP with regard to its ability to produce equally good or even superior results compared to the use of virgin or original mixes if they are properly produced and applied. Among the benefits of RAP mixes are good moisture resistance and higher density. This review also demonstrate the critical importance of using RAP in asphalt mixtures. A well-developed road network is vital for swift economic growth as it links remote areas, provides access to markets, schools, and hospitals, and promotes trade and investment in underdeveloped regions. Roads facilitate inter-modal transport, connecting airports, railway stations, and ports. India\'s road network spans approximately 4.2 million kilometers, making it the second-largest in the world after the United States. This extensive network handles around 65% of freight traffic and 87% of passenger traffic. National Highways (NH), covering about 70,934 kilometers or just 2% of the total network, carry nearly 40% of the road traffic. State Highways (SH) and Major District Roads (MDR) make up the secondary road transport system, playing a significant role in the rural economy and industrial growth of the country. The traditional method of applying bituminous surfacing on flexible pavements requires a substantial amount of energy, as it involves producing bituminous binder from crude petroleum, drying aggregates, and producing the bituminous mix at a hot mix plant (HMP). Hot mix recycling involves combining reclaimed asphalt pavement materials with new materials, often along with a recycling agent, to create hot mix asphalt mixtures. Properly designed recycled mixtures can perform as well as or better than new conventional hot mix asphalt mixtures. Recycling or rejuvenating agents are organic materials with chemical and physical characteristics chosen to restore aged asphalt properties to desired specifications. The viscosity characteristics of the combined aged asphalt binder and recycling agent determine the choice of recycling agent, which can also be called softening agents, reclaiming agents, modifiers, fluxing oils, extender oils, and aromatic oils. The grade of Recycling Agent (RA) used depends on the amount and hardness of the asphalt in the aged pavement. Lower viscosity RA types can restore aged asphalts with high viscosity, and vice versa. Laboratory studies on asphalt mixes with RAP material and rejuvenating agents compared their performance to virgin asphalt mixes. Various performance tests, including Retained Stability, Indirect Tensile Strength (ITS), Creep test, beam fatigue test, resilient modulus, and wheel tracking test, have been conducted to compare the performance properties. This paper presents the results of these performance tests on asphalt mixes with RAP and virgin mixes. Laboratory results indicate that asphalt mixes with RAP and rejuvenating agents provide better performance compared to virgin mixes.

Introduction

Reclaimed Asphalt Pavement (RAP) involves recycling old asphalt materials for reuse in new pavement construction or rehabilitation. It is widely used in the base and surface layers of roads using either cold or hot-in-place recycling methods. RAP is typically obtained by milling or full-depth removal of existing pavements and can be reused after crushing and screening.

Benefits of RAP

• Environmental: Reduces waste and conserves natural resources (aggregates and asphalt binders).

• Economic: Lowers project costs by minimizing the use of virgin materials and expensive binders.

• Performance: RAP materials often offer comparable or even superior performance to virgin mixes, especially in terms of moisture resistance, rutting resistance, and fatigue life.

Material Properties

• RAP consists of high-quality, well-graded aggregates coated with aged asphalt.

• Rejuvenators may be added to restore flexibility to aged asphalt, though some states restrict their use due to concerns over rutting.

• Optimal RAP performance requires balancing mix properties like stiffness, viscosity, air voids, and binder content.

Recycling Methods

1. Hot-in-place Recycling (HIR)

2. Cold-in-place Recycling (CIR)

3. Hot in-plant Recycling (HIP)

4. Cold in-plant Recycling (CIP)

5. Full Depth Reclamation (FDR)

Each method varies based on the temperature and location of recycling.

Research Highlights

1. Gonzalo Valdés et al. (2011): Mixtures with up to 60% RAP showed improved stiffness and fatigue performance compared to conventional mixes.

2. T. Anil Pradyumna et al. (2013): 20% RAP mixes exhibited better moisture resistance, rutting resistance, and fatigue life than virgin mixes.

3. Arshad Hussain & Qiu Yanjun (2013): Binder stiffness increases with RAP content; mix performance depends on the specific binder blend.

4. S.M. Mhlongo (2014): 100% RAP with bitumen addition showed high stability and fatigue resistance, suitable for wearing courses.

5. Ahmed Ebrahim (2015): 100% RAP offered maximum stability and optimum mechanical properties; binder content optimization is crucial.

6. P. Akhilesh Rao (2019): 35% RAP was optimal for maintaining mix stability and reducing cost by up to 50%.

7. Dudhwala Rinkal (2021): RAP over 50% may reduce mix strength; blending with virgin aggregates is recommended.

8. Arindam Karmakar (2023): Adding cement to RAP improves compaction, strength, and long-term durability under moisture variation.

Limitations and Recommendations

• Excessive RAP (typically over 50%) may negatively impact rutting resistance, shear strength, and bearing capacity.

• Some mixes with high RAP content have reduced fatigue life and increased permeability due to the stiffness of aged binders.

• RAP mixtures should meet or exceed the performance of virgin materials.

• Rejuvenators should be used carefully and tailored to the binder’s condition.

Conclusion

A disciplined approach to RAP management — one based on data to manage inventory, process¬ing, uniformity, and quality — will maximize the return on investment in materials, equipment, and people. Good management of RAP begins with collecting or accepting the materials in ways that ensure the materials are not contaminated. Most RAP is obtained through roadway milling opera¬tions. Milling is beneficial to roadway maintenance because it removes distressed layers, helps restore the roadway profile and cross slope, and aids in cre¬ating a strong bond with the overlay. An important decision by the highway agency is determining the appropriate milling depth. Leaving a poorly bonded interface or a moisture damaged layer in the pave¬ment structure is a sure way to a short life for the rehabilitation. RAP from multiple sources can be made into a very consistent material with good stockpiling and processing techniques. An inventory analysis is very helpful to make the best decisions on when and how to process. Good stockpiling practices include build¬ing in layers to help average out variations, avoiding trucks on top of the stockpiles to minimize compac¬tion, and avoiding pushing material over the edge of the stockpile to minimize segregation. The goal of processing RAP is to make a uniform material that meets the needs of mix designs that will use RAP as a component. A decision about processing includes setting the crusher top size to balance the need to utilize the material in a range of mix types versus the generation of additional fines. Fractionating RAP should be a contractor’s choice, not a specification requirement. Fractionating RAP can be beneficial when the RAP supply exceeds the current rate of usage and the plant is capable of producing higher RAP contents, but mixes are unable to meet volumetric or gradation requirements during mix design or quality assurance testing.

References

[1] AASHTO M 323-17. (2017). Standard Specification for Superpave Volumetric Mix design. American Association of State Highway and Transportation Officials. [2] IRC:120-2015. (2015). Recommended Practice for Recycling of Bituminous Pavements. Indian Roads Congress. West, R. C., & Copeland, A. (2015). [3] High RAP Asphalt Pavements: Japan Practice—Lessons Learned. National Asphalt Pavement Association. Al-Qadi, I. L., Elseifi, M., & Carpenter, S. H. (2012). [4] Impact of High RAP Content on Structural and Performance Properties of Asphalt Mixtures. Transportation Research Record, 2294(1), 56–64. Kandhal, P. S., & Mallick, R. B. (1997). [5] Pavement Recycling Guidelines for State and Local Governments. FHWA-SA-98-042. [6] A Critical Overview of Using Reclaimed Asphalt Pavement (RAP) in Road Pavement Construction by Laboratory of Pavement Engineering, School of Civil Engineering, National Technical University of Athens, GR-15773 Athens, Greece. [7] Agencies & contractors surveys on barriers to higher rap usage in asphalt mixtures Jean-Paul Fort, Director, Pavement Engineering & Innovation, NAPA (https://www.asphaltpavement.org) [8] A Review Study on Use of Reclaimed Asphalt Pavement (RAP) Materials in Flexible Pavements by International Journal of Scientific Development and Research (IJSDR) www.ijsdr.org [9] A review of the use of reclaimed asphalt pavement for road paving applications by Jurnal Teknologi (https://www.researchgate.net/publication/340573213) [10] Chapter 3 of Mix design of High RAP usage by www.fhwa.dot.gov/publications/research/infrastructure/pavements/11021/003.cfm [11] The International Journal of Thermal & Environmental Engineering (IJTEE) published Utilizing Reclaimed Asphalt Pavement (RAP) Materials in New Pavements - A Review [12] A Review: Investigation Of The Use Of Recycled Asphalt Pavement (RAP) Material In Economical And Eco-Friendly Road Construction and Rehabilitation Projects by International Journal of Creative Research thought (IJCRT2502436) [13] Best Practices for RAP and RAS Management by Randy C. West (National Asphalt Pavement Association- NAPA)

Copyright

Copyright © 2025 Nikhil Dixit, Bablu Chauhan. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.