Cold recycling process using renewable resources: contribution of rheological and chromatographic methods for rejuvenating mechanism and duration assessment

Abstract

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.

The Effect of a Liquified Wood Heavy Fraction on the Rheological Behaviour and Performance of Paving-Grade Bitumen

“…However, since then, different research studies have reported the limitations of these criteria to avoid the poor field performance of some bitumens [54] or validate the enhanced performance of other bitumens (e.g., polymer-modified bitumens) [55]. Nevertheless, other studies have proposed different rheological-based indicators, which can be expected to be included in the next bitumen specifications, such as in the upcoming revisions of the European standards [56]. In addition, bitumens incorporating biomaterials are non-conventional bituminous binders, and the proposed rheological indicators may not apply to them.…”

“…The other indicators correspond to two stiffness levels (|G*| = 50 kPa and |G*| = 5 MPa) that have been intensively discussed regarding their inclusion in the revisions of the European standards for bituminous binders, despite them requiring for now only the reporting of test values. The temperature at the highest stiffness (5 MPa) is aimed at giving an indication of fatigue cracking performance so that the lower the temperature is, the better the expected performance [56]. In opposition, the higher the temperature for the lower stiffness level (50 kPa), the better the expected performance for rutting resistance [56].…”

“…The temperature at the highest stiffness (5 MPa) is aimed at giving an indication of fatigue cracking performance so that the lower the temperature is, the better the expected performance [56]. In opposition, the higher the temperature for the lower stiffness level (50 kPa), the better the expected performance for rutting resistance [56]. Besides the iso-stiffness temperatures, the phase angles have also been determined.…”