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In the field of highway construction, the application of styrene–butadiene rubber (SBR)-modified asphalt has gained popularity across different levels of road surfaces. A crucial aspect in ensuring the efficacy of this modification lies in the compatibility between SBR and the matrix asphalt. To address this, the current study utilizes molecular dynamics simulation as a technique. By establishing a model for the SBR-modified asphalt mixture, the research quantifies the compatibility level between the SBR modifier and the asphalt. The aim is to uncover the underlying mechanisms of compatibility between the SBR modifier and the base asphalt, ultimately contributing to the improvement of the storage stability of SBR-modified asphalt, which holds significant importance. The investigation began with the creation of models for both the base asphalt and the SBR modifier. A model for the SBR-modified asphalt blending system was then formulated based on these initial models. After undergoing geometry optimization and annealing procedures, the model attained its lowest energy state, providing a reliable basis for examining the performance of SBR-modified asphalt. The study proceeded to calculate solubility parameters and interaction energies of the system to evaluate the compatibility between the SBR modifier and the base asphalt at various temperatures. The analysis of these parameters shed light on the compatibility mechanism between the two components. Notably, it was found that at a temperature of 160 ℃, the compatibility was significantly enhanced. The findings were further corroborated through scanning electron microscope and rheological tests. The outcomes of this research offer theoretical guidance for the application of SBR-modified asphalt. [ABSTRACT FROM AUTHOR]

Non-metallic fractions (NMFs) from waste printed circuit boards (PCBs) are mostly composed of cured resin and fiber. In this study, NMF material from a PCB was ground into powder and added into matrix asphalt to produce PCB-NMF-modified asphalt. To improve the compatibility of PCB-NMF and asphalt, a compatibilizer consisting of tung oil and glycerol was also developed. The optimum compatibilizer content was determined to be 8% by weight of the PCB-NMF through a series of laboratory tests, including the softening point, penetration, ductility, and softening point difference (SPD). The micro-mechanism of NMF powder-modified asphalt was analyzed through Fourier transform infrared spectroscopy (FTIR) and a scanning electron microscope test (SEM). The performances of PCB-NMF-modified asphalt were evaluated by the dynamic shear rheology (DSR) test and the low-temperature bending beam rheometer (BBR) test. The optimum compatibilizer content was 8% by weight of the NMF powder and the optimum content of NMF powder was determined to be 30% by weight of the asphalt based on a comprehensive evaluation. The results show that PCB-NMF can significantly improve stiffness, rutting resistance, high-temperature stability, and temperature sensitivity of asphalt material at an appropriate content. The BBR tests revealed that PCB-NMF slightly weakened the cracking resistance of asphalt at low temperatures. The SEM test showed that the addition of a compatibilizer can increase the compatibility by making the NMF powder evenly dispersed. The FTIR test results implied that a chemical reaction may not have happened between PCB-NMF, compatibilizer, and the matrix asphalt. Overall, it is a promising and sustainable way to utilize PCB-NMF as a modifier for asphalt material and reduce electronic waste treatment at a low cost. [ABSTRACT FROM AUTHOR]

The single light oil regenerating agent has certain limitations on the performance recovery of aged asphalt. In this study, tung oil, dioctyl phthalate (DOP), C9 petroleum resin, and organic montmorillonite (OMMT) were used to prepare the composite regenerating agent, and its optimal mix proportion was determined by the orthogonal experimental design. The rheological properties and anti-aging performance of reclaimed asphalt were studied by the dynamic shear rheometer (DSR) and bending beam rheometer (BBR); and the Fourier transform infrared (FTIR) spectrometer, gel permeation chromatography (GPC), and scanning electron microscope (SEM) were adopted to explore its microstructure, morphology, and mechanism of action. The results show that with the addition of tung oil composite regenerating agent, the rheological properties of aged asphalt can be effectively recovered, even better than that of base asphalt. By using the complex modulus aging index (CMAI) and phase angle aging index (PMAI) it is found that the anti-aging performance of reclaimed asphalt is better than that of base asphalt. With the optimal content of the tung oil composite regenerating agent, the contents of characteristic functional groups and macromolecular asphaltenes in the aged asphalt can be reduced, indicating that the composite regenerating agent is beneficial to the dispersion and dissolution of polar substances in the aged asphalt. After aging, a large number of wrinkles appear on the surface of the asphalt. However, the addition of the tung oil composite regenerating agent can make the asphalt surface smooth, which indicates that the tung oil composite regenerating agent can restore the microstructure and morphology of aged asphalt to a certain extent. [ABSTRACT FROM AUTHOR]

The paper aims to investigate the influence of basalt fiber (BF) on the crack resistance of the asphalt mixture and conduct a mechanical analysis. First, two typical asphalt mixtures, namely AC-13 and SMA-13, were designed. The impact of BF on the mixture design results was analyzed. Then, several macroscopic tests, namely the four-point bending test, indirect tensile test, and semicircular bending test (SCB), were conducted to assess the effect of BF on the cracking resistance of asphalt mixtures. Finally, the influence of BF on the cracking resistance of asphalt mixtures was analyzed based on an environmental scanning electron microscope (ESEM) observation. The results show that: (1) BF increases the optimal asphalt content of AC13 and decreases the optimal asphalt content of SMA-13, which is caused by the different asphalt-absorption capacity of BF and lignin fiber (LF). (2) BF enhances both the fatigue crack resistance and temperature crack resistance of asphalt mixtures. The enhancement on the SMA-13 is more significant, indicating that the enhancement of BF on asphalt mixtures is related to the type of aggregate gradation. (3) BFs in the asphalt mixture lap each other to form a spatial network structure. Such structure can effectively improve the crack resistance of the mixture by dispersing the load stress and preventing the flow of asphalt mastic. The study results provide an effective method to design crack-resistant asphalt mixtures. [ABSTRACT FROM AUTHOR]

Adequate asphalt binder film thickness (ABFT) delivers skeletal integrity in recycled asphalt mixtures, resulting in long-lasting roadways when exposed to traffic and environment. The inaccurate measurement of ABFT and the consequences of not having adequate film thickness model has substantially introduced discrepancies in predicting actual performance of recycled asphalt mixtures. Expansion of the ultra-modern expertise and SuperPave requirements necessitate the revision of authentic ABFT at micro-level. The current study identifies the weaknesses of the current methods of estimating ABFT and provides results that are reliable and useful, using modern measurement methods. Using scanning electron microscope (SEM) and energy dispersive x-ray spectroscopy (EDS), this study measures the ABFT around the tiniest particle of 0.2 μm magnitude, entrenched in asphalt mastic in recycled asphalt mixtures. The ABFT, obtained through image analysis, is compared with those obtained through available analytical models. The study utilizes different asphalt mixtures, containing varying proportions of recycled asphalt mixture and rejuvenators. The aggregate, virgin, and recycled binders were characterized in terms of physical and rheological properties, respectively. Marshall mix design was carried out for the conventional and recycled mixture, containing 40%, 50%, and 60% recycled materials, rejuvenated with 3%, 6%, 9%, and 12% waste engine oil (WEO) at a mixing temperature of 160 °C, based on viscosity of the virgin and rejuvenated binder. ABFT was assessed through analytical models and image analysis for the aforesaid recycled asphalt mixtures, prepared at optimum binder and rejuvenator content as per protocol outlined in ASTM D1559. The analytical estimation of ABFT, in the aforesaid recycled asphalt mixtures, revealed that the ABFT fluctuates from 6.4 μm to 13.7 microns, with a significant association to recycled asphalt mixture and rejuvenator content. However, the image analysis revealed that the ABFT, in the aforesaid recycled asphalt mixtures, fluctuates from 0.4 μm to 2 microns, without any association to recycled asphalt mixture or rejuvenator content. The image analysis indicated that the recycled asphalt mixtures typically comprise of mortar, happening in uneven shape, and are used to grip large aggregates. The asphalt mastic, a blend of bitumen and mineral filler, was found to be an interlocking agent, used to grasp only fine particles in asphalt mortar. The asphalt binder film was discovered to be a deviating stand-alone entity that only exists around the mineral fillers in the asphalt mastic as a non-absorbed binder, occupying an imprecise space of 0.4 μm to 2 microns, among the filler particles. The current findings will be useful to design asphalt pavements through the aforesaid precise limit of SEM-based ABFT rather than traditionally measured ABFT to predict the actual performance of recycled asphalt mixtures. [ABSTRACT FROM AUTHOR]

Recycled construction and demolition (C&D) waste can reduce the rebuild cost, and is environmentally friendly when recycled asphalt pavement (RAP) aggregate constitutes the main part. This paper investigated the mechanical performance of RAP concrete, and the applicability of RAP in road base layers also was discussed. Several mechanical laboratory tests were selected, including the unconfined compressive-strength, splitting-strength, and compressive-resilience modulus tests. The RAP concrete had a good road performance in a cold region, which was proved by the temperature-shrinkage test, dry-shrinkage test, freeze–thaw-cycle test, and water-stability test. Based on various cement dosages from 3.5% to 5.5% in RAP concrete mix design, three RAP aggregate replacement ratios (30%, 40%, and 50%) were selected to study the variation of mechanical properties with increasing curing time, and the optimal aggregate substitute ratio was determined. A scanning electron microscope (SEM) was used to observe the inner-structure interface between the asphalt binder and cement stone. A numerical model is presented to simulate the RAP compressive strength with respect to the effect of multiple parameters. The research results can provide a technical reference for RAP use in the reconstruction and expansion of low-grade highway projects. [ABSTRACT FROM AUTHOR]

Segregation of waste crumb rubber powder (WR) modified asphalt binders the large-scale application of WR in asphalt. The method of microwave activation combined with chemical activation (KMWR) was proposed to improve storage stability and rheological properties of WR modified asphalt in this work. Storage stability and rheological properties of virgin asphalt, MWR modified asphalt, and KMWR modified asphalt were comparatively studied by the standard segregation test, bending beam rheometer (BBR) test, and dynamic shear rheometer (DSR) test. The effect of composite activation on waste rubber powder particles was studied by Fourier-transform infrared spectroscopy (FT-IR), scanning electron microscope (SEM), and Brunauer–Emmett–Teller (BET) tests. The main results showed that after the physical and chemical composite activation, the storage stability of waste rubber powder modified asphalt was significantly improved, WR modified asphalt had better crack resistance, better rutting resistance, and better fatigue performance. After physical and chemical activation, WR was desulfurized, and a large number of active groups was grafted on the WR particles. [ABSTRACT FROM AUTHOR]

In order to study the high and low temperature properties, and fatigue properties, of silica fume/SBS (Styrene-Butadiene-Styrene) compound modified asphalt (SFSCMA), dynamic shear rheometer (DSR) and bending beam rheometer (BBR) are used to study matrix asphalt (MA), silica fume modified asphalt (SFMA) (silica fume (SF) 6%), SBS modified asphalt (SBSMA) (mass ratio of SBS to Matrix asphalt 4%), and silica fume/SBS compound modified asphalt, and the high temperature rheological properties of silica fume/SBS compound modified asphalt with different silica fume additions are also studied. The modification mechanism of SFSCMA was studied by scanning electron microscope (SEM). The investigation results turn out: along with the increase in the content of SF, the high temperature performance of SFSCMA is improved significantly. When the content of SF is 6%, the high temperature performance is the best. When the content of SF is more than 6%, the high temperature property of SFSCMA is lower than that of SBSMA. It is suggested to choose 6% as the content of SF. Compared with MA, SFMA, and SBSMA, SFSCMA has excellent high temperature performance; compared with MA and SFMA, the low temperature performance of SFSCMA is improved, but it is worse than that of SBSMA. Moreover, when the temperature is lower than −30 °C, its low temperature performance is close to that of MA, or even worse than that of MA. After the compound modification of SF and SBSMA, the fatigue properties of the asphalt are improved, and the fatigue performance of SFSCMA is the best among the four kinds of asphalt. There is a cross-linking force in the network structure of SFSCMA, which restrains the flow of the whole system, so that the stability of the compound modified asphalt is significantly improved, which is favorable to the high temperature performance and fatigue resistance of the compound modified asphalt. However, due to its low mobility, it has a negative impact on the low temperature performance of the compound modified asphalt. In addition, according to previous studies, compared with diatomite, it is proven that SF can reach the same level as diatomite in improving the high temperature performance and fatigue performance of asphalt. Therefore, SF can be used as a good choice of asphalt modifier and can achieve the purpose of waste recycling and environmental protection. [ABSTRACT FROM AUTHOR]

Rubberized asphalt (RA) has been successfully applied in road engineering due to its excellent performance; however, the most widely used rubber content is about 20%.To improve the content of waste rubber and ensure its performance, seven rubberized asphalts with different powder content were prepared by high-speed shearing. Firstly, penetration, softening point, and ductility tests were carried out to investigate the conventional physical features of high-content rubberized asphalt (HCRA). Then, the dynamic shear rheometer test (DSR) was conducted to estimate the high-temperature rheological properties. The bending beam rheometer test (BBR) was carried out to evaluate the low-temperature rheological performance. Finally, combined with the macroscopic performance test, the modification mechanism was revealed by the Fourier transform infrared reflection (FTIR) test, and scanning electron microscope (SEM) analysis was used to observe the microscopic appearance before and after aging. The results show that rubberized asphalt has excellent properties in high- and low-temperature conditions, and fatigue resistance is also outstanding compared with neat asphalt. As the crumb rubber content increases, it is evident that the 40% RA performance is the best. The low-temperature properties of HCRA are better than the traditional 20% rubberized asphalt. This study provides a full test foundation for the efficient utilization of HCRA in road engineering. [ABSTRACT FROM AUTHOR]

Studies show that each kind of fiber has its own advantages in improving the properties of asphalt binders. However, there are very limited research studies about mixed fiber-reinforced asphalt (MFRA). In this study, two kinds of fibers, basalt fiber (BF) and lignin fiber (LF), were selected to reinforce SBS (styrene–butadiene–styrene triblock copolymer)-modified asphalt, which is now widely used in pavement engineering. MFRA samples with different fiber mix ratios (FMRs) were prepared for the tests of softening point, ductility, and rheological properties, the micromorphology of which was studied by using scanning electron microscope (SEM). The oil (asphalt) absorption rates of mixed fibers with different FMRs were also tested. The results show that the properties of MFRA were affected by the physical and chemical properties of fibers. Basalt fiber can better strengthen the physical properties of MFRA, while lignin fiber is good for improving the rheological properties, and the oil absorption rate of lignin fiber is higher than that of basalt fiber. Furthermore, the best FMR calculated by the efficacy coefficient method (ECM) was recommended as 1:2 (BF:LF). An interface layer between the fiber and asphalt was observed from the micro images, proving that the fibers bond well with the asphalt. Generally, mixing BF and LF together into SBS-modified asphalt could make full use of the advantages of different fibers and reinforce the comprehensive performance of MFRA better. [ABSTRACT FROM AUTHOR]

The interfacial adhesion between asphalt and steel slag aggregate is a decisive factor in the formation of an asphalt–steel slag mixture and significantly affects the quality stability of steel slag–asphalt mixtures. In this study, the adhesion between an asphalt and steel slag aggregate, the interfacial microstructure, the adsorption and desorption characteristics, and chemical reactions were, respectively, explored by a PosiTestAT–A adhesion puller, a scanning electron microscope, a net adsorption test, an infrared spectrometer, and a dynamic shear rheometer. The mechanism of adhesion between the asphalt and steel slag aggregate was analyzed from the perspectives of physical adsorption and chemical reactions. The results showed that different factors had different effects on the adhesion of asphalt–steel slag aggregate interface. The freeze–thaw cycle and steel slag aggregate particle size had significant effects on interfacial adhesion, while the asphalt heating temperature, water bath time, and stirring time had relatively weak effects on interfacial adhesion. Compared to a limestone aggregate, the steel slag–asphalt mixture had greater adhesion and better adhesion performance because the pits and textures on the surface of the steel slag aggregate produced a skeleton–like effect that strengthened the phase strength of the asphalt–slag aggregate interface, thereby improving the adhesion and increasing the physical adsorption between the asphalt and steel slag aggregate. In addition, due to the N–H stretching vibrations of the amines and amides, as well as SiO–H stretching vibrations, a chemical reaction occurred between the asphalt and steel slag aggregate, thus improving the adhesion performance between the asphalt and steel slag. Based on the shape of the adsorption isotherm, it was determined that the adsorption type was multi–molecular layer adsorption, indicating that the adhesion between the asphalt and steel slag mainly involved physical adsorption. [ABSTRACT FROM AUTHOR]

The fillers of ordinary and pyrolytic basic oxygen furnace (BOF) slag were selected to investigate the properties of their asphalt mastic. XRF (X-Ray Fluorescence) was used to analyze chemical composition of fillers. Meanwhile, SEM (Scanning Electron Microscope) and AIMS (Aggregate Image Measurement System) were utilized to explore meso-morphology, angularity and sphericity. Penetration, softening point and viscosity of asphalt mastic were discussed, while the rheological properties of asphalt mastic were studied by means of DSR (dynamic shear rheometer) and BBR (bending beam rheometer) tests. The experimental results show that chemical composition of different types of BOF slag is similar. The grinding energy consumption of pyrolytic BOF slag is higher than that of limestone and ordinary BOF slag. It is not recommended that pyrolytic BOF slag filler is produced by grinding process. The micro-texture structure of ordinary BOF slag filler is more abundant and their angularity index is about 15% higher than that of limestone filler. The stiffness modulus and rutting factor of asphalt mastic with ordinary BOF slag filler is higher than that of limestone filler. Meanwhile the incorporation of BOF slag filler will further reduce the low-temperature flow performance of asphalt mastic. The effect of pyrolytic BOF slag filler on the performance of asphalt mastic is less than that of ordinary BOF slag. Ordinary BOF slag filler can effectively improve high temperature anti-rutting stability of asphalt mixture. Ordinary BOF slag has a useful application prospect as filler in asphalt mixture. [ABSTRACT FROM AUTHOR]