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The multiple regeneration of aging asphalt pavements has emerged as a pavement maintenance approach. However, the micromechanisms and performance deterioration patterns associated with multiple regenerations remain unclear. The present work aims to investigate the rheological and physicochemical properties of styrenic block copolymers (SBS)-modified asphalt during multiple recycling processes. The rheological properties, nanostructure, and functional group evolution of SBS-modified asphalt during multiple recyclings were evaluated using rotational viscosity, frequency scanning, multistress creep recovery (MSCR), atomic force microscopy (AFM), and Fourier transform infrared (FTIR) tests. The key findings demonstrated that the viscoelasticity of asphalt is affected by both SBS degradation and asphalt aging. During the initial aging phase, SBS degradation mainly affects the asphalt properties, whereas the subsequent aging process becomes the dominant factor. Moreover, the viscoelasticity of the asphalt binder is primarily influenced by aging rather than the SBS degradation. Importantly, the SBS-modified asphalt continues to meet specification requirements even after multiple recycling rounds, demonstrating the feasibility of aging SBS-modified asphalt binder through multiple regeneration techniques. [ABSTRACT FROM AUTHOR]

Investigation of the adhesion mechanism during the aging process of the asphalt-aggregate interface from a microscopic point of view contributes to the solution of water damage of asphalt pavements. So far, some work has been done to reveal the influence of aging on the adhesion strength of the asphalt from the nanoscale factors. However, due to the lack of direct chemical analysis means to test the chemical composition of asphalt at the nanoscale, the inferences made among different scholars are somewhat controversial. The objective of this study is to reveal the evolution of adhesion characteristics of the asphalt binders during the aging process based on their chemical components. Five asphalt binders at different aging degrees were prepared via laboratory simulated aging procedure. State-of-art technologies, atomic force microscopy–based infrared spectroscopy (AFM-IR) and AFM PF-QNM (peak force quantitative nanomechanical mapping) mode, were adopted to analyze the nanoscale adhesion and chemical components of the prepared asphalt. And binder bond strength (BBS) testing was performed to interpret and verify the nanoscale mechanism of asphalt adhesion behavior from macroscale. The results of the AFM test indicated that both sulfoxide and carbonyl functional group content contribute to the adhesion force of the asphalt binders. Compared with the carbonyl group, the sulfoxide content affects the nanoscale adhesion force more significantly. Meanwhile, the results of the BBS test are found in accordance with the AFM trends. Finally, an estimation model was established to roughly estimate the nanoscale adhesion force of asphalt at varying aging conditions based on these two functional groups. [ABSTRACT FROM AUTHOR]

If HT ht , additional tests should be conducted. These factors include the asphalt amount, physical properties of asphalt, the gradation and characteristics of aggregates, and asphalt-aggregate interface characteristics ([3]; [4]). It can be seen that similar to 70# base asphalt, the rutting resistance at high temperatures also can be improved using the elaborated mixing process proposed in the original paper for SBS-modified asphalt and hard-grade asphalt. [Extracted from the article]

[Display omitted] • Propose a novel GPC-based method to assess the aging condition of SBS binder in RAP. • Find suitable chemical composition fingerprinting to estimate SBS binders' properties. • Clarify the change mechanism of polymer and asphaltene in SBS binder due to aging. As fossil energy sources gradually become depleted, the reclamation of recycled asphalt pavement (RAP) has received increasing attention. During the production process of recycled mixtures, the aging conditions of binders in RAP need to be measured prior to the mixing design process. The conventional method adopts chemical solvents, including trichloroethylene and toluene to extract and recovery binders in the RAP. And then measure the corresponding properties of RAP binders. However, the whole process is complicated and time-consuming, and the used chemical solvents are highly toxic and harmful to researcher's health. Some scholars have proposed some methods to test the aging condition of asphalt binders in the RAP directly without extraction and recovery using the novel observation instruments. However, these methods are not suitable for modified asphalt. At present, modified asphalt has been often used in the road construction,especially for SBS modified asphalt. As such, the present study aims to introduce a novel approach to test the aging conditions of SBS modified binders in the mixtures avoiding the extraction and recovery process based on gel permeation chromatography (GPC). For this purpose, the molecular weight distribution as well as the physical properties of modified asphalt and binders in the mixtures at various aging degrees were first analyzed using GPC test. The polymer and asphaltene content of asphalt binders derived from GPC test were found correlation well with the aging degrees and properties of asphalt binders. Following this, several estimation models correlating the polymer and asphaltene content with penetration, viscosity and rutting factor were established. The robustness of established models were verified using laboratory-aged asphalt mixtures with three different SBS modifier contents and two kinds of on-site RAPs. The verification results showed that the properties in the mixture were reasonably estimated. [ABSTRACT FROM AUTHOR]

• An improved mixing process with twice additions of virgin asphalt binder is proposed. • The prediction formula to determine asphalt binder twice additions ratio based on RAP content is provided. • The performance of hot recycled mixtures with improved mixing process is obviously improved. Existing studies have shown that the mixing process of hot recycled asphalt mixture has a considerable effect on its performance. The conventional mixing process applied widely in pavement industry, mixed the RAP and virgin aggregate first. Then asphalt binder was added for the second mixing. This conventional mixing process, however, ignored the asphalt-adsorbing capacity of different aggregates, may resulting in the heterogeneity of recycled asphalt mixture after mixing. Adjusting the mixing sequence of RAP, virgin asphalt binders and aggregate is confirmed as an effective way to solve the above-mentioned issue. However, the change in the demand for virgin asphalt binders for each mixing step, which is raised from aggregate gradation and different RAP content, is not taken into consideration in this improved method. In view of this weakness, this study proposed an improved mixing technique for hot recycled asphalt mixture, which comprehensively considered the mixing sequence of materials and determined the amount of asphalt binders added for different RAP content based on the specific surface area of aggregates. And the prediction formula for the amount of virgin asphalt added each step is further proposed from the perspective of aggregate specific surface area. Several laboratory experiments were conducted to verify the feasibility of this improved technique. The results indicated that, the improved mixing technique could contribute to enhancing the water stability, low temperature cracking resistance and fatigue performance of hot recycled asphalt mixtures. And the higher the content of the RAP used in recycled mixture, the stronger the improvement of the improved mixing process. [ABSTRACT FROM AUTHOR]

• Propose an extraction or recovery free method to assess binder's properties in RAP. • Establish the correlation between aging level of asphalt mixture and binder sample. • Develop a model linking LMS content and physical properties of binders in RAP. Evaluating the properties of asphalt in reclaimed asphalt mixture (RAP) is a crucial step in the design of hot recycled mixtures. The conventional assessment approach involves the extraction and recovery of the aged asphalt with further assessing the aging condition of recovered binders via their penetration, viscosity, and performance-related properties. Since this approach is time-consuming, environmentally unfriendly and involve residue mineral powders that may alter the recovered binder properties, an alternative gel permeation chromatography-based method, requiring no extraction or recovery, was proposed in this study. The gel permeation chromatography (GPC) test were carried out to directly analyze the Large molecular size (LMS) content of unrecovered binders in asphalt mixture samples under different aging conditions, which were prepared via laboratory simulated aging procedure. LMS content was found sensitive in reflecting the aging condition for the binders in the mixture. In addition, the correlation between the aging levels of asphalt mixtures aged under laboratory conditions with those of single asphalt samples was established. Following this, the best-fit regression model linking the LMS content in a mixture sample with the rutting factor, penetration and viscosity were developed. According to the above regression model, the conventional properties of RAP binders were predicted by their LMS content, which can be further applied to assess the aging condition of RAP binders, eliminating the complicated extraction and recovery process. Three sources of on-site RAPs verified the proposed method feasibility: it reasonably estimates the properties of binders in RAP, especially for base asphalt. [ABSTRACT FROM AUTHOR]