Fundamental evaluation of the interaction between RAS/RAP and virgin asphalt binders.

Nazzal, Munir D.; Kim, Sang Soo; Abbas, Ala R.; Qtaish, Lana Abu; Holcombe, Evan; Hassan, Yazeed Abu · 2017 · ROSA P / Ohio. Dept. of Transportation

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Summary

This study investigates the micro-scale interaction between recycled asphalt materials—specifically Reclaimed Asphalt Pavement (RAP) and Recycled Asphalt Shingles (RAS)—and virgin asphalt binders, and how these interactions influence the macro-scale performance of asphalt mixtures. Motivated by rising material costs and environmental goals, the Ohio Department of Transportation increased the use of recycled materials, but concerns persisted regarding the potential for increased cracking and moisture damage due to the aged, stiff nature of recycled binders. The research aimed to characterize the interfacial blending zone between these materials and determine its effect on fatigue, low-temperature cracking, and moisture susceptibility. The research employed a two-part experimental design: a binder study using Atomic Force Microscopy (AFM) and a mixture study using macro-scale mechanical testing. In the binder study, researchers developed a novel sample preparation procedure to simulate the blending of RAP/RAS and virgin binders (PG 58-28, PG 64-28, and PG 64-22) during production. AFM imaging and force spectroscopy were used to measure the micro-structure, stiffness (reduced elastic modulus), and adhesive bonding energy of the interfacial zones. In the mixture study, several asphalt mixtures were designed to meet Ohio specifications, including a control mix, mixes with 30% RAP, 5% tear-off RAS, and a combination of 20% RAP and 3% RAS. These mixtures were evaluated for fatigue resistance using Semi-Circular Bend (SCB) and Indirect Tensile Strength (IDT) tests, for low-temperature cracking using the Asphalt Concrete Cracking Device (ACCD), and for moisture damage using the modified Lottman test. The AFM results revealed that RAP binders blended with virgin binders to varying degrees, creating an interfacial zone whose stiffness depended on both RAP and virgin binder properties, while its adhesive properties were primarily influenced by the virgin binder. Although the adhesive bonding energy in the blending zone was lower than that of the virgin binder, it remained significantly higher than that of the RAP binder. Conversely, AFM analysis showed very limited to no blending between RAS (both manufacturing waste and tear-off) and virgin binders. Macro-scale testing confirmed that this lack of blending negatively impacted mixture performance. The inclusion of 5% tear-off RAS significantly reduced resistance to fatigue cracking, low-temperature cracking, and moisture-induced damage compared to the control mixture. Additionally, increasing the RAP recycled binder ratio reduced fatigue resistance, and the study found that the standard assumption of 18% available binder from RAS was inaccurate, with actual contribution being much lower. The findings imply that the poor blending of RAS with virgin binders is a primary cause of reduced durability in recycled mixtures. Consequently, the authors recommend lowering the maximum allowed RAS content in Ohio Department of Transportation specifications from 5% to 3% and reducing the assumed available RAS binder content in mix designs from 18% to 10%. The study also suggests that linear regression models derived from AFM data can serve as viable tools for selecting appropriate virgin binders for RAP mixtures. Furthermore, it recommends incorporating SCB testing into the mix design process for mixes with high RAP binder ratios or containing RAS to ensure adequate fatigue cracking resistance.

Key finding

The use of tear-off recycled asphalt shingles significantly reduces the resistance of asphalt mixes to fatigue cracking, low-temperature cracking, and moisture damage due to limited blending with virgin binders.

Methodology

lab_experiment

Provenance

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Summary generated by qwen3.6-27b-prismaquant on 2026-06-10; verification: verified.

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• road surface friction