Assessing the effectiveness of recycling agents on reclaimed asphalt pavements

Reclaimed Asphalt Pavements (RAP) are a significant resource for environmentally friendly road building techniques. RAP is obtained from millings when the pavement loses its quality by aging, and it needs to be removed when brand-new asphalt is needed. There are many challenges on any form of recycling agent in order to restore the aged asphalt binder in RAP, despite the growing interest in its use. Even so, there is still no agreement on how to employ RAP and rejuvenators. It is crucial to have an in-depth understanding of how they affect the rheological characteristics and performance of pavements to use recycling agents in asphalt mixtures at their fullest potential. This study investigates the use of recycling agents in RAP applications to shed light on the potential advantages and difficulties connected to recycling agents with their use together with RAP. In order to understand the effects of recycling agents on asphalt pavements, the Laboratory of Road Materials at Politecnico di Torino brings a new methodology, called Model System (MS). Model System consists of two main structures. It focuses on single-size aggregate (sieve No.4, size 4.75 mm) to limit the finer fractions and clumps in RAP MS samples. Secondly, MS has the target of 30% Voids in Mineral Aggregate (VMA). Materials are sieved, compacted to cylindrical shape in its original state or cold treated with different types of recycling agents. By using the single-size aggregate and 30% VMA volumetric properties, it is anticipated that the binder phase will have a major impact on the eventual response and limiting the aggregate interlocking effect. Model Systems with 100% RAP so-called Black System, Model Systems with recycling agents called Rejuvenated System, and Model Systems with extracted aggregate (by ignition oven) and treated with virgin binder called White System. Each model system was tested by Indirect Tensile Cracking Test at intermediate temperature. Test results are analyzed to obtain certain parameters (i.e., CTIndex) to have a broader understanding of the effect of recycling agents by comparing the Black, Rejuvenated, and White Systems. According to analysis, recycling agents have demonstrated potential in improving the properties of aged asphalt binders. Rejuvenators improve the workability and distress resistance of RAP-containing asphalt mixes. However, depending on variables like RAP source, granular gradation, binder grade, and environmental conditions, certain recycling agents may not always be as effective as others.