Potential and limits of FTIR methods for reclaimed asphalt characterisation
Faculty of Applied Engineering Sciences
Publication type
Engineering sciences. Technology
Source (journal)
Materials and Structures
47(2014) :8 , p. 1273-1286
Target language
English (eng)
Full text (Publishers DOI)
University of Antwerp
In recent years, as a result of both envi-ronmental policy and industrial economic strategy, the amount of asphalt pavement that has been recycled has risen dramatically. As a result of this, several inter- national research projects have shown the need for improvements in reclaimed asphalt (RA) character- isation to support these higher recycling rates. During the life of a pavement, as well as the structural damage induced by traffic, the intrinsic properties of asphaltic materials are affected through the oxidative ageing of the bituminous binder. The molecular changes asso- ciated with this oxidation can be monitored via variations in Fourier transform infrared (FTIR) spec- tra. Therefore, if the relationships between binder properties, such as penetration, softening point and complex shear modulus and the spectra parameters can be established, the characterisation of RA pro- duced by the milling of old pavements can be greatly improved. However, the interpretation of oxidation parameters from these spectra is not straightforward, and many different techniques are used to calculate them in the asphalt community. This paper gives a brief overview of asphalt oxidation and the FTIR principle. It then presents the results from four different calculation methods for the oxidation param- eters applied to a set of more than 100 spectra obtained during the RILEM TC-ATB-TG5 round robin test. From this study, it is obvious that the conclusions of the analysis performed on the same set of raw spectra can differ considerably according to the FTIR oxida- tion index calculation method adopted. Using the RILEM database, the potential links between a given ageing index and the physical properties are then evaluated. As a result of this study it can be concluded that ageing comparison through FTIR should be considered as relative and restricted for use in measurements at different ageing steps on the same type of initial mixture. For FTIR spectra to be comparable between different laboratories, harmoni- sation of the data acquisition procedures is needed. Also the different calculation methods of the oxidation indicators seem to reflect different physical properties. So a first step toward harmonisation would be to agree on the relevant physical properties actually needed for efficient RA characterisation. This could then lead to a common FTIR index calculation method, which would reflect the properties of interest. For this, additional research is needed to improve knowledge of the relationship between the chemical oxidative process of a binder and the evolution of its physical properties