Abstract
The recycling of road and airport asphalt pavements requires greater reliability of mix design in order to ensure proper rehabilitation and effective reuse of recycled asphalt concrete. Currently, internationally, the most effective mix design procedures for recycled asphalt concrete with RAP (Reclaimed Asphalt Pavement) refer to guidelines developed by SuPerPave® Mixtures Expert Task Group. In this paper, according to the requirements of the European standard EN 13108, the authors investigated the reliability of the above mix design procedure. In particular, the SuPerPave® mix design guidelines were applied for dosing components of wearing course layer recycled asphalt mixture and for the determination of PG (Performance Grade) and critical temperatures of binder contained in RAP (RAP binder) and of binder added ex-novo (virgin binder). The experimental research program started from RAM (Reclaimed Aggregate Material) grading characterization and RAP binder content determination. Afterwards, rheological characterization of the RAP binder and selected virgin binder was carried out using the DSR (Dynamic Shear Rheometer) and BBR (Bending Beam Rheometer) devices. This step allowed us to identify the right virgin binder percentages to be added to RAP binder. Then, in compliance with European standards, the mix design study of recycled mixtures was carried out, identifying the necessary granulometric integrations and the virgin-binder-appropriate percentages to be added. In this phase, three different RAP percentages were used: 30%, 40%, and 50%. Finally, the experimental plan was completed with a preliminary mechanical characterization of the studied recycled asphalt mixtures. The results showed that the implemented rational mix design guarantees performance levels of wearing course layer recycled mixtures that are fully in compliance with European standards.
Highlights
In the perspective of sustainable development, the road construction field offers several solutions, among which the recycling of damaged road pavements is the most important
The rolling thin film oven (RTFO)-aged reclaimed asphalt (RAP) binder was subsequently tested with a Bending Beam Rheometer (BBR) in order to determine the critical Low Tc (S) and Tc (m) temperatures, which correspond to a stiffness equal to 300 MPa and an m-value equal to 0.3, respectively: log300 − logS1
The guidelines developed by the SuPerPave® Mixtures Expert Task Group allow for the mix design of recycled asphalt concrete to be approached in a rational way
Summary
In the perspective of sustainable development, the road construction field offers several solutions, among which the recycling of damaged road pavements is the most important. The NCHRP specifications set limits for the use of RAP and RAS in asphalt mixtures, referring to their percentage by weight of total aggregate weight This approach does not properly evaluate either the aged binder content in RAP and RAS or the overall performance characteristics of the blended binder [21]. In Europe, the use of RAS in road pavements is even more limited [17] Based on these considerations, the authors believe that it is permissible to neglect (especially in the European context) the use of RAS and, the present study was conducted adopting as its reference the SuPerPave® mix design guidelines defined in NCHRP Report 452 [16,24]. From an economic and environmental point of view, the use of high RAP percentages in road surface layers results in significant savings due to the reduced use of virgin high-quality aggregates
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