A Review on Bitumen Rejuvenation: Mechanisms, Materials, Methods and Perspectives

Abstract

This review aims to explore the state of the knowledge and the state-of-the-art regarding bitumen rejuvenation. In particular, attention was paid to clear things up about the rejuvenator mechanism of action. Frequently, the terms rejuvenator and flux oil, or oil (i.e., softening agent) are used as if they were synonymous. According to our knowledge, these two terms refer to substances producing different modifications to the aged bitumen: they can decrease the viscosity (softening agents), or, in addition to this, restore the original microstructure (real rejuvenators). In order to deal with the argument in its entirety, the bitumen is investigated in terms of chemical structure and microstructural features. Proper investigating tools are, therefore, needed to distinguish the different mechanisms of action of the various types of bitumen, so attention is focused on recent research and the use of different investigation techniques to distinguish between various additives. Methods based on organic synthesis can also be used to prepare ad-hoc rejuvenating molecules with higher performances. The interplay of chemical interaction, structural changes and overall effect of the additive is then presented in terms of the modern concepts of complex systems, which furnishes valid arguments to suggest X-ray scattering and Nuclear Magnetic Resonance relaxometry experiments as vanguard and forefront tools to study bitumen. Far from being a standard review, this work represents a critical analysis of the state-of-the-art taking into account for the molecular basis at the origin of the observed behavior. Furnishing a novel viewpoint for the study of bitumen based on the concepts of the complex systems in physics, it constitutes a novel approach for the study of these systems.

NMR Diffusiometry Spectroscopy, a Novel Technique for Monitoring the Micro-Modifications in Bitumen Ageing

“…Figure 1 shows a schematic splitting of bitumen into its main components. The proposed model of bitumen in the literature is that the asphaltene, in the form of polar nano-aggregates, remains dispersed as a peninsula or group of peninsulas within a more apolar continuous maltene phase [8]. In the conventional colloidal model, the resins-to-asphaltenes ratio characterizes the bitumen behavior to a specific path if the bitumen is in solution (sol).…”

New Experimental Approaches to Analyse the Supramolecular Structure of Rejuvenated Aged Bitumens

“…The purpose of the present contribution is to emphasize the potentialities of advanced experimental methods such as scattering techniques and nuclear magnetic relaxometry, which can be considered promising techniques in the elucidation of the dynamics of the complex microstructure in bitumen. In fact, unlike the results acquired through the analysis of the mechanical bulk properties, scattering (in particular X-ray scattering) and NMR experiments can probe from nano-to mesoscale level the effectiveness of a rejuvenator in restoring the microstructure of bitumen subjected to the drastic action of aging processes [18,19]. This work underlines that the detailed analysis of the microstructural dynamics of bitumen, extending the information taken from commonly used empirical and rapid methods, allows us to better understand the phenomena that occur in such complex materials, providing new tools for the piloted design of ever-performing rejuvenations.…”

“…Experimental methods. Information on how rejuvenators can affect the supramolecular structure and distribution of aggregates within the bituminous colloidal network and how this may affect the overall material properties can be achieved from careful analyses of Powder X-Ray Diffraction (PXRD) data and NMR measurements performed at low magnetic fields ( 1 H-NMR Relaxometry), making these techniques very powerful methods to carry out structural investigation in such complex systems [18,20].…”

Effect of Aging on Chemical Composition and Rheological Properties of Neat and Modified Bitumen

“…The most significant properties linking the structure of the bitumen with its behaviour and rheology are the glass transition temperature of the maltenes and the effective content of asphaltenes [1]. These affects can be determined using scattering techniques (such as Atomic Force Microscopy (AFM), Scanning Electron Microscopy (SEM) and Fluorescence Microscopy, X-ray and other) and nuclear magnetic relaxometry, which are used for deeper analysis in ageing and rejuvenation of bitumen [16].Oxidative hardening is imposed on the polar, oxygen-containing chemical components on bitumen molecules, causing increased molecular interactions and resulting in bitumen hardening [17][18][19]. Bitumen aging takes place during bitumen production (in refinery), storage, and transportation, asphalt mixing, asphalt mixture transportation and compaction, as well as from environmental impact over the pavement service life.…”

“…The most significant properties linking the structure of the bitumen with its behaviour and rheology are the glass transition temperature of the maltenes and the effective content of asphaltenes [1]. These affects can be determined using scattering techniques (such as Atomic Force Microscopy (AFM), Scanning Electron Microscopy (SEM) and Fluorescence Microscopy, X-ray and other) and nuclear magnetic relaxometry, which are used for deeper analysis in ageing and rejuvenation of bitumen [16].…”