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The rheological properties of the styrene–butadiene–styrene modified asphalt (SBSMA) binder have not been thoroughly investigated yet. In this study, SBSMA binders with various SBS contents and base asphalt types were prepared and analysed. Fluorescence microscopy, temperature sweeping, and multiple stress creep recovery (MSCR) tests were conducted to analyse the phase structure and rheological behaviour of SBSMA. The results indicate that the special rheological behaviour of a decreasing phase angle value in SBSMA as the temperature increases is a result of the gradual dominance of the network structure over SBSMA's rheological behaviour. Results from MSCR tests indicate that with the increase in stress levels, the elasticity of the network structure gradually diminishes, signifying a significant stress sensitivity in the network structure. Consequently, due to the stress sensitivity of the network structure, traditional rheological indicators measured at low stress levels (such as phase angle, elastic recovery rate) may overestimate the elasticity of SBSMA at high temperatures (40–80°C). [ABSTRACT FROM AUTHOR]

Master curve technique is frequently used to characterize the linear viscoelasticity of polymer modified asphalt (PMA), however, there is no widely accepted master curve for PMA. This study aims to propose a novel double sigmoidal model that can be used universally for all asphalts, especially highly modified PMAs. To do so, one plain asphalt and six representative PMAs are examined. Extended temperature sweep tests (−40°C to 140°C) are conducted to grasp the whole picture of the master curve. Three representative mathematical models (CAM, sigmoidal, double sigmoidal) are selected and compared in terms of fitting in both modulus and phase angle. The results suggest that double sigmoidal model suits all types of asphalts for all testing temperature ranges, and it features the ability to model the rubbery state and rubbery-viscous transition of highly modified PMA (RMSE < 0.02). A phase angle expression of the double sigmoidal model is also developed, which shows great potential in characterizing the strength of polymer network within the PMA. Also, it avoids the impact from the partial break of the time-temperature superposition principle (TTSP) and reveals the true shape of the phase angle master curve. Finally, master curve models are recommended based on different testing temperature ranges. [ABSTRACT FROM AUTHOR]

In order to understand the contribution of asphalt components to thermoreversible aging, the extended bending beam rheometer (Ex-BBR) test, SARA fractions separation, and thermal analysis were performed on a series of asphalt binders from different sources. The results indicated that thermoreversible aging is not an inherent characteristic of asphalt, and some binders were not affected by thermoreversible aging. Grade loss caused by thermoreversible aging showed a high correlation with wax content in asphalt but had no apparent relationship with asphaltenes content and colloidal structure index used. Moreover, the thermal analysis results well explained the degree of thermoreversible aging in the asphalt binder. Finally, the endothermic peak and crystallites formed in asphalt binder could have resulted from the long side chains in naphthene aromatic molecules. [ABSTRACT FROM AUTHOR]

The cold recycled mixture has insufficient resistance to cracking, and the process of fracture is incompletely understood. This study used digital image correlation (DIC) technology and a semi-circular bending test to investigate the anti-crack performances and fracture propagation of basalt fiber-reinforced cold recycled mixture (BFCRM). The load-displacement, full-field strain, full-field displacement, displacement rate and crack propagation map were obtained to evaluate the BFCRM's anti-crack performances. The control cold recycled mixture without fibers was also prepared for comparison. Meanwhile, the fracture process zone (FPZ) during loading were compared and quantitatively assessed by digital image correlation analyses, and the fiber distribution and microscopic features at fracture surface was observed by scanning electron microscopy. The results show that the formation of microcracks of BFCRM takes more time than that of the control group without fiber. Based on DIC observations, the basalt fibers maintain strong anti-crack performance in cold-recycled mixtures and reduce fracture damage. The fracture surface morphology also revealed that basalt fiber exhibited adsorption, bridging, anchoring, stability, and strengthening effects at micro/nano scale, which further improved anti-crack performance e and hindered crack development of cold recycled asphalt mixtures. [ABSTRACT FROM AUTHOR]

Semiflexible pavement (SFP) is attracting increasing interest due to its exceptional load-carrying capacity. However, there is limited understanding of its cracking performance and mechanisms. This study investigated the suitability of the emerging cracking resistance parameters, the flexible index (FI) and cracking resistance index (CRI), derived from the semicircular bending (SCB) test, in elucidating the mid-temperature resistance of SFP mixtures against cracking. The influence of styrene-butadiene-styrene-modified asphalts and styrene-acrylic emulsion/styrene-butadiene rubber-modified cement mortars on the anticrack property of SFP mixtures was also determined. Results indicated a high correlation (R2=0.95) between the FI and CRI of various SFP mixtures, with CRI exhibiting more promise than FI in assessing the fracture resistance of SFP mixtures due to its higher discrimination potential and lower variability. Enhancing the bending strength of cement mortar or increasing the CRI/Nf value of asphalt binder were identified as effective means to improve the anticracking ability of SFP. Therefore, improving the binder toughness of both cement mortar and asphalt is essential for enhancing the performance of SFP against cracking. [ABSTRACT FROM AUTHOR]

To investigate the effect of pre-shredding as a replacement for high-speed shearing in the preparation process of SBS-modified asphalt, the particle size and mixing time of pre-shredded SBS modifier were studied. Laser confocal microscopy was used to observe the morphological changes and dispersion state of the SBS modifier during the mixing process, and process parameters were determined through rheological performance tests. FTIR tests were conducted on the original asphalt and PAV-aged modified asphalt to assess the impact of the pre-shredding process on the chemical composition and aging resistance of the modified asphalt. The specific conclusions were as follows. During the preparation process of the SBS modifier using low-speed mixing, the morphological changes of the SBS modifier can be summarized as follows: It cycles through edge networking, mesh fiberization, and filamentous granulation, and eventually presents a granular atomization form after multiple cycles. It is recommended that the mixing time be maintained between 30 and 60 min, which results in the microstructure of the modified asphalt consisting of filamentous and point-like combinations. This asphalt exhibited excellent performance in high-temperature rut resistance, fatigue resistance, and low-temperature crack resistance. When the mixing time was too long, the SBS modifier formed small granules in an atomized state, which weakened the strength of the mesh structure and led to a decrease in overall performance. It is recommended that the SBS be shredded into particles sized between 18 and 30 mesh or 30 and 100 mesh. SBS-modified asphalt with SBS particles sized between 18 and 30 mesh exhibited greater hardness in the mesh structure, resulting in better high-temperature rut resistance. SBS-modified asphalt with SBS particles sized between 30 and 100 mesh had better extensibility in the mesh structure, leading to superior performance in medium-temperature fatigue resistance and low-temperature crack resistance. Compared to the conventional process, the pre-shredding process for preparing SBS-modified asphalt improved aging resistance by 10% to 13%. Additionally, SBS-modified asphalt prepared using the pre-shredding process saved 1 to 3 h of processing time compared to the traditional preparation method, reducing energy consumption. Furthermore, the asphalt produced through the new process exhibited better performance, reducing road wear and saving maintenance costs. [ABSTRACT FROM AUTHOR]

Inertia effect is an artifact commonly seen in the oscillation test for soft materials. It is due to the misattribute of the instrument's elastic component to the sample's properties, which will lead to overestimated storage modulus (G′) and underestimated phase angle (δ). Inertia effect is widely recognized for bio materials; however, it has not been fully understood for asphalt binder. This article aims to investigate the instrumental inertia effect in the asphalt binder oscillation test. In this study, one plain asphalt, eight elastomeric modified asphalts (EMAs), and six non-elastomeric modified asphalts (non-EMAs) are examined using the oscillation test for a wide temperature range (40°C–140°C). The inertia effects that occurred during the testing are characterized and discussed. It is found that inertia effects also happen to asphalt binders, especially for non-EMA. The existence of inertia effect can be identified by the raw phase parameter being greater than 90°. Increasing the strain amplitude of the oscillation test may alleviate the inertia effect. This might be due to the improved signal/noise ratio of the data. To eliminate the inertia effect artifact during the asphalt binder oscillation measurement, this study recommends a stress-control oscillation test (50 Pa), combined with a lower strain limit of 1% and an upper strain limit of 100%. The results suggest that by using the stress-control approach, the inertia effect can be eliminated and accurate measurements for G′ and phase angle can be obtained. [ABSTRACT FROM AUTHOR]