Abstract
Bitumen is a crucial building material in road construction, which is exposed to continuously higher stresses due to higher traffic loads and changing climatic conditions. Therefore, various additives are increasingly being added to the bitumen complicating the characterisation of the bituminous binder, especially concerning the reuse of reclaimed asphalt. Therefore, this work aimed to demonstrate that the combination of Fourier transform infrared (FTIR) spectroscopy with attenuated total reflexion (ATR) technique and multivariate evaluation is a very well-suited method to reliable identify and quantify additives in bituminous binders. For this purpose, various unmodified and modified binders, directly and extracted from laboratory and reclaimed asphalts, were investigated with FTIR-ATR spectroscopy. The determined spectra, pre-processed by standard normal variate (SNV) transformation and the determination of the 1st derivation, were evaluated using factor analysis (FA), linear discriminant analysis (LDA) and partial least square regression (PLSR). With this multivariate evaluation, first, a significant model with a very high hit rate of over 90% was developed allowing for the identification of styrene-butadiene copolymers (SBC), ethylene-copolymer bitumen (ECB) and different waxes (e.g. amide and Fischer-Tropsch wax) even if the additives do not show any additional peaks or the samples are multi-modified. Second, a quantification of the content is possible for SBC, ECB, and amide wax with a mean error of RMSE ≤ 0.4 wt% and a coefficient of determination of R2 > 90%. Based on these results, FTIR identification and quantification of additives in bituminous binders is a very promising method with a great potential.
Highlights
As a crucial element of our infrastructure, roads are essential for the modern economy and society
Thereby, four different paving grade bitumen according to EN 12591 [21] from two different refineries (A and B) designated 20/30 A, 50/70 A, 70/100 A and 70/100 B were modified with various additives commonly used in Germany including styrene–butadiene copolymers (SBC) and ethylene-copolymer bitumen (ECB) as polymers as well as amide wax, FischerTropsch wax (FT wax) and montan wax A and B (Mo A, Mo B) as waxes
In addition to the self-modified binders, binders being already modified from the manufacturer were obtained, including especially the polymer-modified binders 25/55-55 A according to EN 12591 [21] from the two refineries A and B and 40/100-65 A according to EN 12591 [21] from refinery A
Summary
As a crucial element of our infrastructure, roads are essential for the modern economy and society. In Germany, the essential criterion is the softening point ring and ball (TR&B), which may assume a maximum of 70 °C to limit the ageing state of the binder [3]. This criterion was initially developed for unmodified bitumen. Bitumen is increasingly modified with additives to improve the asphalt properties, save resources, or protect the environment and health These modified binders often have relatively high softening points caused by the additives and not by an advanced ageing. Different studies could show that, with these methods, various information about the structure and properties of bituminous binders and other petroleumbased products could be gained [17,18,19,20]
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