Oxidative aging induces significant stiffening of asphalt binders that leads to a pronounced reduction in the overall durability of asphalt pavements. The strategic implementation of antioxidant additives provides a potential solution to alleviate this issue. This work presents results from the second phase of the global consortium for antioxidants research aimed at investigating the effectiveness of potential antioxidants in increasing the durability of asphalt binders. Sixteen laboratories around the world participated in this effort and a total of 28 binders from diverse geographical regions were tested. Two promising antioxidants, namely zinc diethyldithiocarbamate (ZDC) and kraft lignin were evaluated in this phase and blended with the binders at specific proportions. Subsequently, a comprehensive investigation was conducted to assess rheological characteristics and chemical properties of the various blends, utilising Dynamic Shear Rheometer (DSR) measurements and Fourier Transform Infrared (FTIR) Spectroscopy. The findings indicate that additives such as ZDC hold considerable promise as an effective antioxidant, particularly when considering a wide diversity of binders. In general, its incorporation does not compromise the rutting performance of the binders and significantly improves fatigue performance. Therefore, research efforts should be focused on exploring additional facets to assess its practical applicability in field.

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Generally, rejuvenators are used to supply missing components of aged asphalt, reverse the aging process, and are widely used in asphalt maintenance and recycling. However, compared with traditional rejuvenators, bio-oil rejuvenators are environmentally friendly, economical and efficient. This study looks into the effect of the three different bio-oils, namely sunflower oil, soybean oil, and palm oil, on the physical properties, rheological properties and chemical components of aged asphalt at different dosages. The asphalt physical properties and Dynamic Shear Rheological (DSR) test results show that with the increase in bio-oil, the physical properties and rheological properties of rejuvenated asphalt are close to those of virgin asphalt, but the high-temperature rutting resistance needs to be further improved. The results of Fourier Transform Infrared Spectroscopy (FTIR) show that the carbonyl and sulfoxide indices of rejuvenated asphalt are much lower than those of aged asphalt. Moreover, the rejuvenation efficiency of aged asphalt mixed with sunflower oil is better than that with soybean oil and palm oil at the same dosage. @en

The design and use of antioxidant additives to reduce or slow down the aging of asphalt binders can bring about tremendous benefits to the asphalt industry. Despite many isolated and scattered research efforts showing mixed results, the application of this science to engineering-based solutions has been limited due to variability in results and conflicting data available. This work presents the results from a global interlaboratory study to test the effectiveness of promising antioxidant additives, namely kraft lignin, calcium hydroxide, zinc diethyldithiocarbamate and phenothiazine to increase the resilience of asphalt binders and provide insights towards understanding the complex intricacies between chemistry and rheology. Specifically, seven different binders from various geographical regions in the world i.e., Texas (USA), Vienna (Austria), Illinois (USA), Antwerp (Belgium), and Delft (Netherlands) were blended with the antioxidants at two proportions. Subsequently, the chemical and rheological properties of the blends were evaluated using Fourier transform infrared (FTIR) spectroscopy and dynamic shear rheometer (DSR). The results indicate that although some antioxidants may reduce oxidation based chemical indices, their effect on rheology is more complicated and possibly related to unique physicochemical interactions in each binder. From a macro-perspective, zinc diethyldithiocarbamate showed promising results with a good correlation between rheology and chemistry for the majority of the binders. These additives or other additives with the same working principles should be investigated further. Additionally, significant research efforts must also be directed towards approaches aimed at understanding mechanisms of interaction and relating results with specific binder compositions.@en

Correction to: Materials and Structures (2022) 55:146 https://doi.org/10.1617/s11527-022-01986-w

The article “Do chemistry and rheology follow the same laboratory ageing trends in bitumen?”, written by Georgios Pipintakos, Caitlin Lommaert, Aikaterini Varveri and Wim Van den bergh, was originally published in volume 55, issue 5, ID 146 without open access. With the society's decision to grant Open Choice the copyright of the article changed in February 2023 to © The Author(s) 2022 and the article is forthwith distributed under a Creative Commons Attribution 4.0 International License, which permits use, sharing, adaptation, distribution and reproduction in any medium or format, as long as you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons licence, and indicate if changes were made. The images or other third party material in this article are included in the article’s Creative Commons licence, unless indicated otherwise in a credit line to the material. If material is not included in the article’s Creative Commons licence and your intended use is not permitted by statutory regulation or exceeds the permitted use, you will need to obtain permission directly from the copyright holder. To view a copy of this licence, visit http://creativecommons.org/licenses/by/4.0. Open access funding enabled and organized by RILEM.

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The ageing of bitumen has received great attention both from a chemical and rheological perspective due to its direct impact on asphalt performance. However, open questions with respect to the convergence of the synchronous ageing changes in rheology and chemistry of bitumen still exist. This paper addresses these alterations of chemistry and rheology and attempts to establish a link via fitting rheological equations fed by fundamental chemical information. To that end, three binders of different type were used in four different laboratory ageing states. A number of spectroscopic techniques and rheological testing were employed to derive corresponding chemical and rheological parameters. In parallel, various statistical methods (Bivariate analysis, Wilcoxon test, Factor analysis) assisted in identifying relationships among the chemo-rheological parameters and simplifying the number of variables. The results of this study demonstrate that chemistry and rheology are following similar changes when considering laboratory ageing following the fast-rate phase of a dual oxidation scheme and short-term lab ageing. Finally, this work manages to establish a linking framework for a number of newly-introduced rheological parameters. All in all, the results of this study might be particularly interesting for future interventions in the chemical composition of bitumen, considering its effect on performance.

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The fatigue resistance, as a performance indicator, is of paramount importance for the selection and benchmarking of bituminous materials. The bituminous mortar can be considered as the medium that connects and envelopes the coarse aggregate skeleton, and hence will significantly influence the fatigue resistance at bulk-scale. Therefore this study presents the steps and challenges of a new testing framework to evaluate the fatigue resistance of bituminous mortars. To do so, first, a new test geometry is introduced, which will ensure cohesive failure in a predefined area. The integrity of this sample geometry is assessed theoretically through finite element simulations and by computer tomography scans. Secondly, specimens of the new geometry are evaluated experimentally using a dynamic shear rheometer, where time-sweep tests are performed on two control mortar types under various test conditions. The control mortar types are fabricated using two commercial bituminous binders, one modified and one neat binder, to evaluate the effect of binder type. The test results are comprehensively analysed using fundamental dissipated energy-based concepts but also empirical and phenomenological failure criteria, providing insights into the failure evolution. For the tested mortar types, the analysis shows good convergence with the considered fatigue models. Finally, using dissipated energy concepts led to the most consisted fatigue model, which is independent of binder type and test conditions.

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Understanding the fundamental mechanisms of oxidative ageing in bitumen is considered of paramount importance in order to take steps towards durable binders able to tackle distresses related to this phenomenon which deteriorates the asphalt performance. This paper focuses on the identification of the intermediate and final oxygenated products after short- and long-term laboratory ageing simulated with rolling thin-film oven testing (RTFOT) and pressurised ageing vessel (PAV) respectively. Three binders were investigated in this study, two originated from the same wax-free crude source, while the third was obtained from a different source, containing natural wax, and followed a different manufacturing process. Fourier-Transform Infrared (FTIR) spectroscopy demonstrated a clear increase of the sulfoxide and carbonyl functional groups upon ageing for all the binders independently of origin, manufacturing or performance. Electron Paramagnetic Resonance (EPR) spectroscopy showed an increase of the organic carbon-centred radicals after short-term ageing (RTFOT), whereas after PAV these radicals remained constant in the two wax-free binders originating from the same crude source, and even decreased for the third, waxy binder. Proton Nuclear Magnetic Resonance (¹H NMR) spectroscopy reported differences in the relative distribution of protons between the binders in the unaged state, and similar minor changes after both ageing steps regardless of the binder's crude source and distillation. The results of Time-of-Flight Secondary Ion Mass Spectrometry (TOF-SIMS) revealed that SO_x- and (OH)_x-containing compounds are produced after the sequentially occurring short- and long-term ageing in both wax-free bitumens, whereas an almost constant behaviour of aliphatics after PAV ageing can be seen for the same bitumens. Finally, the strengths and weaknesses of each of these experimental techniques were reviewed and compared versus the obtained results and possible ageing mechanisms.

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Oxidative ageing in bituminous materials is considered to be one of the most important factors for distress types in road applications. The increasing interest in oxidative ageing has highlighted the need for a thorough understanding of the oxidation mechanisms at molecular level. This paper offers some insight in the validity of the proposed hypotheses about the oxidation routes of bitumen, the fast- and the slow-rate route, reflecting on previous studies. Fourier-Transform Infrared (FTIR) and Electron Paramagnetic Resonance (EPR) spectroscopy were utilised for this verification. To elucidate the uncertain formation of sulfoxides, an additional surface investigation with Time-of-Flight Secondary Ion Mass Spectrometry (TOF-SIMS) was performed. The findings of the aforementioned techniques reveal the existence of the oxidation products reported previously and contribute to the understanding of the oxidation mechanisms. Overall, this research strengthens experimentally the hypotheses of the dual-oxidation routes of bitumen.

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Oxidative ageing in bituminous materials is considered one of the most important factors for distress types in road applications. This paper aims to offer insights into the validity of commonly held beliefs regarding the oxidation phases of ageing in bitumen, the fast- and the slow-rate phase, and explore the main oxidation products formed upon ageing. In order to evaluate possible differences between bitumen types, the penetration grade as well as the bitumen production process was varied. Thus, the ageing of three different binders was first studied by Fourier-Transform Infrared (FTIR) and Electron Paramagnetic Resonance (EPR) spectroscopy. The formation of oxygen-containing molecular structures on the bitumen surface during ageing was studied with Time-of-Flight Secondary Ion Mass Spectrometry (TOF-SIMS). The results of FTIR reveal a gradual increase of sulfoxides upon ageing, while the EPR results show an increase of organic carbon-centred radicals. In parallel, TOF-SIMS results provide evidence for an increase of oxygenated compounds, such as SO_x^--, HO_x^-- and NO_x^--containing compounds. It appears also that paramagnetic metal species, such as vanadyl-porphyrins, are insusceptible during ageing. Overall, the findings of this study are in agreement with a mechanism comprising two rate-determining phases and support the formation of different oxygenated products. It is believed that the experimental approach used in this work may contribute further to an improved understanding of the ageing mechanisms in bitumen.

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