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The current trend in the asphalt industry is to increase the utilization of recycled asphalt pavement (RAP). In general, there are two types of RAP binder in RAP aggregates, the mobilized RAP binder and the immobilized RAP binder. The former can be blended into the virgin binder to coat aggregates during asphalt blending, while the latter can be treated as black rocks because they have already become an outer crust of RAP aggregates. Studies have focused on the mobilized RAP binder quantification and the significance of mobilized RAP binder to mixture performances. However, it remains unknown whether the immobilized RAP binder affects mixture performances. This study developed a laboratory procedure for immobilized RAP aggregates preparation and investigated the contribution of immobilized RAP binder to asphalt-aggregate interaction as well as the performance of 100% recycled asphalt mixtures. The work of adhesive energy and the K-B-G* model were adopted to characterize the asphalt-aggregate interaction for asphalt mortar. Resilient modulus and dissipated creep strain energy were used to evaluate the stiffness and cracking resistance of 100% recycled asphalt mixtures. Results showed that the immobilized RAP binder can strengthen the asphalt-aggregate interaction and improve the cracking resistance of 100% recycled asphalt mixtures by increasing total asphalt content. However, if the total asphalt content remains the same, the immobilized RAP binder increases stiffness but decreases the cracking resistance of 100% recycled asphalt mixtures. [ABSTRACT FROM AUTHOR]

Research on the aging process of styrene-butadiene-styrene block copolymers (SBS) block copolymers modifier has practical significance in guiding the recycling of SBS-modified asphalt pavement. The objective of this study is to investigate the aging process of SBS modifier under various oxygen and thermal conditions to address the variations of physical properties and chemical reaction during the service life of recycled asphalt pavement (RAP). In the proposed testing process, SBS modifier was thermal oxidative and vacuum thermal aged at different temperatures and time prior to blending with base asphalt to prepare SBS-modified asphalt. SBS modifier was first dissolved by carbon tetrachloride (CCl4) and then tested through infrared (IR), gel permeation chromatography (GPC), and thermogravimetric (TGA) tests to investigate the variations on microstructure and chemical compositions of aged SBS modifier. The effect of aged SBS modifier on performance of SBS-modified asphalt was evaluated by comparing the mechanical and chemical properties of base and SBS-modified asphalts. Based on the results of the experimental program, appearance variation, modifying effects, and chemical reaction of SBS modifier under oxygen condition were obviously different from that of vacuum condition. The chemical reaction of SBS modifier was not significant at vacuum and high temperature condition, instead, a small amount of degradation was observed. Degradation of mechanical performance of SBS-modified asphalt was mainly caused by aging of base asphalt. Therefore, the SBS modifier in the RAP was suggested to be considered in the mixture design. [ABSTRACT FROM AUTHOR]

With the continuing increase in the use of recycled asphalt pavement (RAP) and recycled asphalt shingle (RAS) for highway construction, there is a concern over how much of the aged asphalt binder inside RAP/RAS can be blended into virgin asphalt binder. In this study, the RAP/RAS binder mobilization rates of 13 different mixtures produced by three different types of asphalt plants in Tennessee were determined using fluorescence microscopy and gel permeation chromatography (GPC). A multiple regression model was developed to explore the factors critical to enhancing the mobilization rate of the RAP/RAS binder. Results showed that the RAP/RAS binder mobilization rate was significantly lower than 100% for most mixtures, indicating that only part of the RAP/RAS binder was mobilized during the production process. The mixing and delivery temperatures had significant influence on the mobilization rate of RAP/RAS binder. In addition, the aging degree of RAP/RAS binder also significantly affected the mobilization rate. [ABSTRACT FROM AUTHOR]

• The intermolecular interaction between virgin and aged asphalt. • The interaction affected the mixed binder performance. • The interaction degree was related to the chemical difference of binders. The mixing process of virgin and aged asphalts is the essential of the rejuvenation of recycled asphalt pavement. The molecular association of asphalt may be decomposed and reconstructed due to the intermolecular interactions while virgin and aged asphalts are blended together. This study investigated the mixing effect between virgin and aged asphalts use rotational viscometer (RV), gel permeation chromatography (GPC) and molecular simulation methods. The high temperature viscosity of the mixed binder was tested by RV, which indicates that the viscosity of the mixed binder was not a linear superposition of virgin and aged asphalt. The GPC was used to test molecular weight of virgin, aged and mixed binders. The comparison between tested and calculated GPC curves shows that the molecular weight of the mixed binder was not the superimposed of virgin and aged asphalts. The molecular simulation indicates that the asphaltene and resin molecules had a tendency of gathering together. The mixing of two asphalt binders with different chemical structures could narrow the distance between aggregated molecules. [ABSTRACT FROM AUTHOR]

The incorporation of high percentage (>30%) recycled asphalt pavement (RAP) into asphalt mixtures has become more popular. Various methods have been proposed to determine how much of RAP binder can be effectively blended into virgin binder. However, few methods can be used to test the blending efficiency of plant-produced asphalt mixtures. This study proposed a method of measuring the blending efficiency of plant-produced mixtures using Fourier Transform Infrared Spectroscopy (FTIR). Three types of asphalt mixtures, including one warm mix, two hot mixes with or without rejuvenator, were used to validate the proposed method. Results indicate that RAP particles varied in oxidation, but mixing RAP binder with virgin binder could reduce this heterogeneity. Among the three mixtures, warm mix showed the highest blending efficiency, while adding rejuvenator had a limited effect on the blending efficiency. The proposed method was further verified using Gel Permeation Chromatography (GPC). [ABSTRACT FROM AUTHOR]

The recycling of asphalt shingles in pavement construction is beneficial to the environment and industry by reducing the consumption of virgin materials. However, current approaches of utilizing recycled asphalt shingle (RAS) by mixing with soft asphalt or rejuvenator were questionable for the anti-aging problems. This study developed a new approach to recycle asphalt shingles, in which the RAS binder was dissolved and extracted by a mixed solvent of heptane and trichloroethylene (TCE). In the proposed process, the viscosity of the extracted RAS binder was controlled by the polarity and composition of the mixed solvent. Results indicate that heptane dissolved the soft part and trichloroethylene (TCE) could dissolve the stiff part of RAS binder. The use of the mixed solvent of heptane and TCE with a certain proportion through the proposed method could prepare asphalt binder with desired properties. The current approaches of utilizing RAS were compared with the proposed method. Results indicate that the anti-aging properties of extracted RAS binder using the proposed method were better since the soft asphalt could not dissolve RAS binder at 170 °C, and the binder blend of RAS binder and rejuvenator had a potential anti-aging problem because an obvious loss of rejuvenator existed during the aging process. The performance test suggests that the high and low temperature region of the extracted RAS binder was close to 75.2–28 °C, which could be used as a common asphalt in pavement engineering. • RAS binder was extracted and used as common asphalt. • Heptane and TCE were mixed to prepare the mixed solvent. • Soft asphalt could not dissolve RAS binder. • Rejuvenator was evaporated seriously during the short aging process. [ABSTRACT FROM AUTHOR]

• The bottom-up crack was more prone to propagate under periodic eccentric load. • The bottom-up crack propagation velocity increases with its crack tip height. • The bottom-up crack propagation acceleration decreases with its crack tip height. • The bottom-up crack propagation life was predicted by simulation and regression. The bottom-up crack (BUC), one kind of reflective crack that initiates at the bottom of asphalt layer and propagates upwards, has become one of the major distresses of asphalt pavement. The Mode Ⅰ dominated bilinear cohesive zone model (CZM) after calibration was introduced into finite element (FE) model to simulate the BUC propagation in asphalt pavement under displacement load. The mechanism of crack propagation under different types of periodic load was analyzed based on two indexes from Mode Ⅰ dominated bilinear CZM. The FE model and corresponding periodic load were modified to limit the occurrence of top-down crack propagation. A combined method based on the developed model was adopted to predict the BUC propagation velocity at varied heights and the remaining life of pavement. The results showed that the acceleration of BUC propagation decreased with the crack tip height. Moreover, the predicted remaining life of pavement based on the proposed method was reasonable referring to the engineering design specifications. [ABSTRACT FROM AUTHOR]

• A tire-pavement dynamic friction analyzer (TDFA) was developed. • Friction properties of asphalt mixtures were tested by TDFA in the lab. • The actual contact area closely relates to the dynamic friction coefficient. • Pavement macrotexture noticeably influences the peak value of friction coefficient. • The mechanism of skid resistance can be studied in depth in pavement mix design. This study proposes a newly developed real-time testing system, namely, a tire-pavement dynamic friction analyzer (TDFA), to measure the dynamic friction coefficient between tire and pavement. Based on the self-developed TDFA, the friction coefficient between tire and pavement can be measured in real-time in the lab. A number of working conditions of tires were mimicked and tested. Subsequently, the effect of parameters such as tire load, tire pressure, actual tire-pavement contact area, tire speed, and slip ratio on pavement friction were investigated. It is found that there is a closely linear correlation between the actual tire-pavement contact area and the dynamic friction coefficient (DFC), and such correlation differs with the variation of pavement types. DFC usually has a negative linear relationship to tire speed. As slip ratio varies from 0% to 100%, the strongest correlation between DFC and Mean profile depth (MPD) can be found at the interval of 10%–15% slip ratio, which indicates that the pavement macrotexture also plays a role in the peak value of friction coefficient for the asphalt pavement. This testing method is very promising for the estimation of friction properties of pavement in the phase of lab mix design. It may also be used in the materials selection for pavement design. [ABSTRACT FROM AUTHOR]