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To promote the construction of environmentally friendly, sustainable pavements and solve the impact of the scarcity of asphalt resources on highway development, bio-mixed asphalt (BMA) modified by SBS and polyphosphoric acid (PPA) was prepared, and the influence of the ratio of bio-asphalt (BA) replacing petroleum asphalt on different PPA/SBS blending schemes was explored through conventional property tests. According to each PPA/SBS blending scheme, the optimal replacement ratio of bio-asphalt was optimized, and the microstructure and distribution morphology of different PPA/SBS-modified BMA were evaluated. Conventional property test results show that with the same PPA/SBS content, the replacement ratio of bio-asphalt has a significant impact on the conventional performance of composite-modified asphalt, but the appropriate replacement ratio of bio-asphalt can improve the storage stability and conventional performance of composite-modified asphalt; in micromorphological analysis, it was found that the number of bee-like structures on the surface of the modified BMA decreased significantly, which indicated that the molecular heterogeneity of various components in the asphalt was reduced. In addition, bio-asphalt changed the particle morphology and improved the dispersity of SBS in asphalt. The composite-modified BMA had a lower SBS content, but its conventional performance was still excellent—so it has significant application prospects in road engineering. [ABSTRACT FROM AUTHOR]

Photocatalytic pavements materials are being developed to purify toxic automobile exhaust gas, especially in tunnels where the pollution concentrations are high. This study investigated the photocatalytic efficiency and pavement performance of asphalt mixtures containing steel slag and different contents of CeO2 and TiO2 as photocatalyst materials. Photocatalytic testing equipment was developed to calculate the photodegradation efficiency for CO, CO2 , NO, and HC. The pavement performance of the asphalt mixtures was evaluated using rutting tests and low-temperature bend tests. The texture depth was measured to evaluate the antislide performance. The excessive addition of the CeO2 and TiO2 nano photocatalysts had an adverse effect on the pavement performance of the steel slag asphalt mixture. The optimal contents of CeO2 and TiO2 were 7% and 0.6% by weight of the asphalt binder weight, respectively, as obtained by a gray target decision process based on principle component analysis. These findings are expected to contribute to the development of functional pavement materials that improve the surrounding air quality and have a lower environmental impact due to the use of waste slag. [ABSTRACT FROM AUTHOR]

In this study, we evaluate the flame-retardant properties of styrene-butadiene-styrene (SBS)/layered double hydroxide (LDH-) –modified asphalt. We performed physical tests, dynamic shear rheological tests, and limit oxygen index measurements to evaluate basic physical properties as well as rheological and flame-retardant properties of SBS/LDH-modified asphalt samples. Fourier transform infrared spectrometry and fluorescence microscopy were performed to elucidate the mechanism reaction between LDH and SBS-modified asphalt. In addition, a novel flame-retardant analyzer was developed and used to analyze the changes in mass and temperature during asphalt combustion. Kinetics analysis and thermogravimetry measurements were performed to determine the most probable mechanism and activation energy. The microstructure of the combustion residue was analyzed using scanning electron microscopy. The results indicate that LDH increases the viscosity of SBS-modified asphalt and its resistance to deformation at high temperatures. However, when added in high concentrations, it has a negative effect on asphalt ductility. The |G*| , G′ , and G″ values for the SBS-modified asphalt increase with the addition of LDH. However, the effect is not statistically significant over the entire investigated frequency range. Moreover, the addition of 5% LDH reduces the phase angle of SBS-modified asphalt for frequencies greater than 30 Hz. Also, its effect is not statistically significant over the entire investigated temperature range. LDH increases the nonflammable grade and activation energy of SBS-modified asphalt and results in the formation of denser char, which significantly improves its flame-retardant properties. [ABSTRACT FROM AUTHOR]

Moisture susceptibility plays an important role in the damage of asphalt pavement. Failure occurs when asphalt is removed from the aggregate particles due to the decreased adhesion between the asphalt and aggregate in comparison with that between water and the aggregate. In recent years, efforts utilizing nanomaterials to improve the diverse properties of asphalt have proven to be effective. In this study, three types of nanoclays were used to modify styrene-butadiene-styrene- (SBS-) modified asphalt. The resistances to water damage of the modified binders were evaluated using the surface free energy (SFE) and atomic force microscopy (AFM). The results revealed that the total SFE decreased and the energy ratio (ER) increased when the asphalt binder was modified with the nanoclays, indicating that the addition of nanoclays can improve the moisture resistance of these aggregate-binder systems. After immersion, a decreased amount of bee structures was observed in both the SBS and nanoclay-modified asphalts due to the interactions between water and bitumen. However, the residual amount of bee structures was higher in the nanoclay-modified asphalts than in the SBS-modified asphalt, indicating that the addition of nanoclay makes the surface morphology of asphalt more resistant to water damage. Finally, freeze-thaw splitting tests were used to verify the results obtained through the SFE and AFM tests. [ABSTRACT FROM AUTHOR]

Asphalt pavements are widely used in road engineering owing to their good skid resistance, ease of maintenance, and high driving comfort. However, large amounts of toxic fumes are produced during petroleum asphalt heating, asphalt mixture preparation, and pavement construction. This review clarifies the fuming mechanisms and hazards of asphalt fumes with the aim of promoting the application of fume-suppression asphalt(s) and reducing the emission levels of asphalt fumes. First, starting from the fuming mechanisms of hot asphalt, the composition and hazards of asphalt fumes are described. Second, existing indoor and on-site asphalt fume testing methods are discussed. Finally, the inhibitory effects and mechanisms of different types of fume suppressants are discussed separately to provide a reference for the popularization and application of fume-suppression asphalt. The review shows that the existing descriptions of the fume-generation mechanisms are based on physical phenomena, and there is a lack of systematic research at the chemical level. An indoor asphalt fume test is usually conducted using a fume-generation and collection device, where the main test object is an asphalt binder. Therefore, it is difficult to simulate real fuming conditions in these tests. A field testing mainly evaluates the concentrations of different types of asphalt fumes, and there is a lack of standardization of asphalt fume test methods and emission specifications. Existing asphalt fume suppressants mainly include polymers, flame retardants, warm mixing agents, adsorbents, and nanomaterials; traditional fume suppressants such as polymers, flame retardants, and warm mix agents have poor fume-suppression effects or reduce the pavement performance. Meanwhile, nanomaterial-based fume suppressants have good fume-suppression and improved pavement performance to some extent; however, they are still in the early stages of exploration. Therefore, future research should focus on asphalt fume-generation mechanisms, asphalt fume-evaluation methods and specifications, and environmentally friendly nanomaterial-based fume suppressants. [Display omitted] • The asphalt fuming mechanism in different construction stages were summarized. • The test methods of asphalt fume were discussed in detail from the perspective of indoor test and field test. • The inhibitory effect, mechanism and working performance of different fume suppressants were classified and summarized. [ABSTRACT FROM AUTHOR]

Waste crumb rubber (CR) can be used in asphalt pavement construction to develop eco-friendly and sustainable pavements. The objective of this study was to investigate the reaction mechanism, high-temperature properties, thermal stability, and volatiles released by CR-modified asphalt (CRMA) activated using microwaves (i.e., ACRMA). The chemical characteristics determined via Fourier-transform infrared spectroscopy revealed that mainly physical reactions occurred in the CRMA before and after activation; however, the swelling reaction in the ACRMA was more efficient than that in the CRMA. These results were confirmed by gel permeation chromatography and atomic force microscopy. The high-temperature performance of the ACRMA was slightly better than that of the CRMA. Additionally, according to stress creep and recovery test results, the microwave activation reduced the stress sensitivity of the rubber-modified asphalt. Thermogravimetric curves indicated that the microwave activation reduced the decomposition temperature of the rubber-modified asphalt. Moreover, the total amount of released volatiles for the base asphalt was significantly larger than that for rubber-modified asphalts, indicating that the CR suppressed the total amount of released volatile gases from the asphalt during the pyrolysis of asphalt. But the addition of CR can increase the release of some toxic gases in CRMA and increase the toxicological potential of asphalt fumes. However, in the initial pyrolysis of rubber asphalts, microwave treatment can reduce the generation of toxic gases. In the later stages of this process, the introduction of rubber particles before and after activation has little effect on the released volatiles. [ABSTRACT FROM AUTHOR]

Effective approaches are required to be developed to solve the poor compatibility and thermal stability problems of crumb rubber-modified asphalt (CRMA). This study focuses on a method called microwave activation. However, seldom researches pay attention to the properties of MACRMA after aging. The objective of this study was to prepare microwave-activated CRMA (MACRMA) and investigate the performance of asphalt after aging. The samples were subjected to thin-film oven test (TFOT) at different times and temperatures. The effect of heat aging on the properties of MACRMA was evaluated by three indicator tests: viscosity, dynamic shear rheology test (DSR), and repeat creep recovery test (RCRT). The test results indicated that the MACRMA after two aging conditions had noticeably lower performance values (e.g., penetration, ductility) compared to unaged samples, and thus, the need to control temperature and time for mixing and construction was verified to be important. In addition, the G*/sin δ and phase angle values were largely influenced by the TFOT aging temperature and time. The MACRMA's ability to recover was improved after aging. Compared with the aging temperature, the aging time had a more significant effect on the deformation and recovery ability of MACRMA. [ABSTRACT FROM AUTHOR]

This study proposes the incorporation of waste steel slag and waste rubber into asphalt to prepare asphalt mastic with increased mechanical properties and can thus concurrently limit environmental pollution from these wastes. The surface of crumb rubber (CR) was activated by NaClO and was then treated with KH550 silane coupling modifier. Dynamic shear rheometer (DSR), multi-stress creep recovery (MSCR) and zero shear viscosity (ZSV) tests were applied explore the high temperature performance of asphalt mastic. The performance of asphalt mastic was analyzed by Burgers model, and the enhancement mechanism was analyzed by Fourier transform infra-red (FTIR) spectroscopy, scanning electron microscopy (SEM), energy dispersive X-ray (EDX), fluorescent microscopy (FM), and X-ray diffraction (XRD). Experimental results showed that coupling modified CR improved the complex modulus (G*) and rutting factor (G*/sinδ) and reduced the temperature sensitivity of asphalt mastic. The coupling modified CR increased the elasticity coefficient E 1 , viscosity coefficient η 1 , relaxation time η 1 /E 1 and delay time η 2 /E 2 of asphalt mastic by 2.8 times, 3.6 times, 1.3 times and 0.9 times, respectively, while steel slag powder (SSP) further enhanced the mechanical properties of the asphalt mastic. FM test showed that coupling modifier CR promoted the swelling of CR and SBS polymer, and hence resulted in a well-developed cross-linked network structure in the asphalt. The positive effect of SSP on the high temperature properties of asphalt mastic suggests that the use of SSP and CR in pavement engineering provides a sustainable solution for the disposal of industrial wastes and the preparation of new asphalt mastic with higher mechanical and thermal properties for practical applications. [Display omitted] • The crumb rubber was modified by secondary treatment. • Burgers model was used to analyze the viscoelastic behavior of asphalt mastic. • The feasibility of CR with steel slag powder in road engineering was demonstrated. • Coupling modified CR promoted the network structure in modified asphalt mastic. • A sustainability analysis of the application of CR and SSP in asphalt was performed. [ABSTRACT FROM AUTHOR]

[Display omitted] • The virgin-old recycling slowed the thermal-oxidative aging by physical approach. • The change in molecules affects the viscosity more than the fatigue performance. • The increase in viscosity was mainly attributed to macromolecules weight increased. • The proportion of the dispersion medium affected the fatigue resistance potential. This study aimed to investigate the thermal-oxidative aging and virgin-old recycling behavior of SBS polymer modified asphalt. For the same, the four-component method, the Fourier transform infrared spectroscopy (FTIR), and the gel permeation chromatography (GPC) test were adopted for characterizing five types of asphalt binders. Besides, Brookfield rotary viscosity and time scan tests were conducted for measuring the rheological parameters of the asphalt samples. The results indicated the following: (i) Thermal-oxidative aging deteriorated the fluidity and performance stability of the asphalt. The aromatic ring index, I C=C , was able to reflect the change in the temperature sensitivity of the asphalt during the process of aging. (ii) After thermal oxidation, the increase in viscosity was mainly attributed to the increase of asphalt macromolecules weight. A reduction in the proportion of the dispersion medium in the asphalt colloid structure was observed to be the main reason for its decreased fatigue resistance potential. (iii) By adding fresh asphalt, the virgin-old recycling approach slowed the thermal-oxidative aging, primarily due to physical integration. (iv) In this study, the asphalt viscosity-temperature properties were more sensitive to molecular changes than fatigue properties. [ABSTRACT FROM AUTHOR]