This recommendation is based on the results of an inter-laboratory study organised by the RILEM technical committee TC 264-RAP "Asphalt Pavement Recycling"—Task Group 3 (TG3) focusing on Asphalt Binder for Recycled Asphalt Mixture. The TG3 aimed to evaluate the effect of a specific family of materials known as asphalt recycling agent (ARA) on the aged binder under different configurations. Even though ageing is an irreversible phenomenon, effective ARA must have the capability to improve the flexibility of the bituminous materials and their resistance against cracking susceptibility with no adverse effect on the rutting resistance of pavements containing reclaimed asphalt. A total of 17 participating laboratories analysed the properties of binder blends composed of aged binder from reclaimed asphalt in three different contents (60, 80, 100%), ARA and virgin binder. The physical properties of the blends were thoroughly evaluated through traditional and rheological binder testing. This recommendation proposes to restore the original material properties at low and intermediate temperatures (i.e. cracking resistance) while balancing the high-temperature characteristics (i.e. rutting susceptibility) with durable impact throughout the progression of ageing phenomena. Therefore, useing of the Dynamic Shear Rheometer is foreseen as a more suitable and sustainable means to evaluate binder blends containing an asphalt recycling agent. Compared with conventional testing, the proposed approach requires fewer materials while resulting in a faster experimental procedure with one single test.
Recycling end-of-life road products can be performed in various ways, involving a combination of sustainable techniques. A first level in sustainability is reached by the use of a bitumen emulsion, which enables processing at moderate temperatures. This technique is already commonly used, according to specific guidelines. Further improvement is achieved if the emulsion contains a rejuvenating agent manufactured from renewable resources. In this context, the key issue in laboratory study is to find a proper way to highlight the rejuvenating effect and to follow its evolution. Suitable test methods, described in this paper, have been identified and used for this purpose. The general principle is to compare binder characteristics after extraction from RAP, and from mixes obtained after recycling process and in situ-aging ; several aging steps are considered. The rejuvenating effect is supposed to end when the characteristics of binder from mix after recycling are back to those of the RAP binder. Dynamic Shear Rheometer (DSR) enables to determine the binder stiffness modulus as a function of temperature: thus, thermal sensitivity is monitored, along with binder hardness. In the first weeks after recycling process, the binder tends to soften, due to the progressive rejuvenating effect. Afterwards, the binder hardens slowly throughout months. After 1 year in situ, a rejuvenating effect is still observed. Chromatographic methods such as gaseous chromatography (simulated distillation) enable to monitor the chemical evolution of the rejuvenating agent itself, within the blend with RAP binder and rejuvenation bitumen. After 1 year aging in situ, the rejuvenating agent is no longer detected, through its effect can still be seen though rheological properties. Considering results obtained by both kinds of techniques, a hypothesis can be proposed, in order to explain the action mechanism of the rejuvenating agent. This latter is most likely to have delayed binder hardening. Hence, the efficiency of rejuvenating process has been improved by lengthening its effect, in comparison with performances attributed to a pure bitumen emulsion.
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