In plant production of hot recycled mixtures with high reclaimed asphalt pavement content: A performance evaluation

Nevertheless hot recycling process is nowadays a widespread technique, many doubts related to the in plant recycling process effects on the performance of recycled mixtures still exist and limit the maximum allowable amount of Reclaimed Asphalt Pavement (RAP). Therefore, the feasibility of an efficient production of plant hot recycled mixtures characterized by high RAP content and suitable performance should be properly addressed. To this aim, the overall performance of hot recycled asphalt mixtures produced in asphalt plant and containing high RAP content were assessed in this study. The mixtures were prepared with two different bitumens (high and low content of SBS polymer modifier) and 40 % of RAP only deriving from asphalt layers containing polymer modified bitumens. The aggregate grading curve was previously optimized through a specific laboratory study by applying the Bailey Method and using selected RAP. A third mixture, currently used for binder layers in motorway pavements, was also studied for comparative purposes. Compactability, stiffness, cracking and rutting resistance and fatigue behavior were investigated. Results of the mechanical tests suggest that mixtures containing 40 % RAP are suitable for the production of new asphalt pavements, especially when low modified bitumens are used. In fact, the performance of such mixtures were comparable or even higher than those of the reference mixture. In particular, the specific and accurate mix design allowed the potential drawbacks due to higher RAP content to be balanced. © RILEM 2016

Modeling and assessment of self-healing and thixotropy properties for SBS modified binders

The fatigue endurance limit of binders is the results of more phenomena (e.g. viscoelasticity, damage, healing, thixotropy, steric hardening) that interact simultaneously making the mechanisms behind the fatigue behavior not properly understood. Currently, there is no consolidated analytical approach inclusive of such phenomena to characterize fatigue performance. This research proposes a criterion to determine the fatigue resistance of binders subjected to monotonous cyclic loading with multiple rest periods. The main rheological properties are measured during each stage using a Dynamic Shear Rheometer and the modeling of their evolution is proposed. The experimental program includes different binders in order to investigate the effects of SBS modification levels and aged binder contents on self-healing potential and fatigue behavior. The proposed criterion enables to identify fundamental contributions leading to a comprehensive fatigue endurance limit. This approach allows different binders to be distinguished taking into account their self-healing capacity and can help to establish a better correlation with in-service performance of mixtures. Moreover, a comparison with a previous analytical approach based on the same kind of test (time sweep) with only one rest period is proposed in order to evaluate the effectiveness and reliability of the proposed criterion. Results show that multiple rest periods are needed in order to fully understand the self-healing and fatigue behavior of bituminous binders and to quantify the contributions given by thixotropy. © 2014 Elsevier Ltd. All rights reserved

Original Approach to Predict Fatigue Endurance Limit of Asphalt Binders Considering Healing Capacity

More phenomena interact (e.g. viscoelasticity, damage, healing) contributing to the overall behavior of binders in terms of fatigue endurance limit. However, currently there is no consolidated analytical approach inclusive of strength recovery during rest periods to characterize fatigue performance. This research proposes a criterion to determine the resistance of binders subjected to monotonous cyclic loading with multiple rest times by using a Dynamic Shear Rheometer. Main rheological properties are measured and the modeling of their evolution during each stage is proposed. The experimental program includes different binders in order to investigate the effects of SBS modification levels and aged binder contents on healing potential. Beyond the classical component related to damage analysis, the proposed criterion enables to identify other fundamental contributions, leading to a comprehensive fatigue endurance limit. This approach allows distinguishing binders taking into account their healing capacity and should provide a better correlation with in-service performance of mixtures

Performance Evaluation of Cold Recycled Mixture Containing High Percentage of Reclaimed Asphalt

Cold recycling of asphalt pavements proved to be an effective maintenance and rehabilitation technology for both environmental and economic reasons. Nevertheless, the use of cold-recycled (CR) asphalt mixtures requires a careful assessment of their mechanical properties, especially when they are designed to replace traditional hot-mix asphalt concrete (AC) mixtures. In this study, the potential use of a CR asphalt mixture as base course of an Italian motorway was evaluated. The studied mixture was produced in a central plant employing high-reclaimed asphalt (RA) content and used to construct two experimental sections along an in-service Italian motorway. In particular, a special mixing procedure, involving the use of water vapour and bituminous emulsion, was tested. A third experimental section was constructed with the same layer thickness using the AC mixture currently used in rehabilitation projects, incorporating 30% of RA. Volumetric properties, stiffness, resistance to permanent deformation and fatigue behaviour of mixtures were investigated by performing tests on samples cored from the three test sections and on laboratory-compacted samples. Results of the mechanical tests showed that CR mixtures provide lower stiffness modulus and lower resistance to repeated loading, but better resistance to permanent deformation when compared with AC. This behaviour can be explained due to the presence of cementitious bonds that reduce thermal sensitivity and viscous response

Low-temperature mechanics of hot recycled mixtures through Asphalt Thermal Cracking Analyzer (ATCA)

Thermal cracking is recognized as a critical failure mode for bituminous mixtures and good fracture properties are a key factor to obtain long lasting asphalt pavements in cold climate. Investigating this aspect in hot recycled mixtures with high amount of Reclaimed Asphalt Pavement (RAP) is fundamental due to the stiffening effect of aged bitumen that can emphasize the cracking aptitude of the mixture when subjected to thermal stresses. An innovative tool for characterizing the low-temperature cracking behavior of asphalt mixtures is the new developed Asphalt Thermal Cracking Analyzer (ATCA). It allows the evaluation of several parameters (e.g. glass transition temperature, coefficients of contraction, cracking temperature) directly related to the mechanics of low-temperature performance. In this study, four recycled asphalt mixtures were produced in laboratory with 40% of RAP using the Bailey Method as tool to optimize the aggregate structure. Different binder contents and modified bitumens (with various level of polymer modification) were employed. An additional mixture with 25% of RAP was used as control mixture. All the mixes were tested using the ATCA device. Moreover, an original image analysis was performed to assess at a microscale level the effects of compaction properties and aggregate structure on thermal cracking response. Results show that mixtures with 40% of RAP can behave better than the control mixture at low temperature if an accurate mix design is performed. Careful selection of RAP material and type and quantity of virgin bitumen can enhance low temperature performance and aggregate packing although high amount of RAP aggregates