Peifeng Cheng

Foaming technology can effectively reduce the viscosity of polymer-modified asphalt and significantly decrease energy consumption during pavement construction, making it an effective approach for achieving low-carbon pavement construction and maintenance. However, mechanically foamed asphalt relies on specialized equipment and requires strict parameter control. Although water-based foaming methods using zeolites or ethanol can alleviate these issues to some extent, they still present disadvantages such as significant variability in foaming performance and potential risks during transportation and construction. Therefore, this study investigates the feasibility of using crystalline hydrates with high water of crystallization for micro-foamed asphalt. Three types of micro-foamed SBS-modified asphalt (MFPA) were prepared using hydrates with different contents of water of crystallization. Physical property tests, foaming characteristic parameters, viscosity–temperature analysis, Fourier transform infrared spectroscopy (FTIR), adhesion tensile tests, scanning electron microscopy (SEM), and fluorescence microscopy were conducted to evaluate their effects on the physical and chemical properties, viscosity reduction performance, adhesion, and compatibility of SBS-modified asphalt. Furthermore, dynamic shear rheometer (DSR) tests, bending beam rheometer (BBR) tests, fatigue life modeling, and morphological analysis were employed to investigate the rheological properties, fatigue life, and bubble evolution behavior of the MFPA system. The results indicate that utilizing the thermal decomposition characteristics of crystalline hydrates with high water of crystallization (Na₂SO₄·10H₂O, Na₂HPO₄·12H₂O, and Na₂CO₃·10H₂O) to release H₂O and CO₂ in SBS-modified asphalt for micro-foaming is a short-term reversible physical viscosity reduction process. The maximum expansion ratio (ERmax) of MFPA reaches 8–10, the half-life (HL) remains stable at approximately 180 s, and the foaming index (FI) peak is about 1160. The construction temperature can be reduced by 10–15%, and the viscosity reduction effect remains stable within 60 min. Compared with unfoamed SBS-modified asphalt, the compatibility, rutting resistance, and fatigue life of MFPA increase by approximately 65%, 32%, and 30%, respectively, while the low-temperature performance decreases by 18%. Under the same short-term and long-term aging conditions, MFPA exhibits better aging resistance. Specifically, its rutting resistance increases by 37%, and fatigue resistance improves by 30% compared with aged SBS-modified asphalt, while the low-temperature performance remains essentially unchanged.

The foaming process effectively reduces the viscosity of asphalt, thereby lowering energy consumption during mixture construction. However, conventional foamed asphalt production depends on specialized equipment and strict control of foaming conditions. Incorporating additives that contain water of crystallization to induce micro-foaming in asphalt presents a promising alternative. In this study, three highly crystalline hydrates, namely KAl(SO ₄ ) ₂ · 12H ₂ O, Na ₂ CO ₃ · 10H ₂ O, and Na ₂ HPO ₄ · 12H ₂ O, were introduced into base asphalt to achieve micro-foaming. The effects of the micro-foaming process on the physical properties and chemical structure of asphalt were evaluated through ductility, penetration, softening point, viscosity, and Fourier-transform infrared spectroscopy (FTIR). Additionally, dynamic shear rheometer (DSR) and bending beam rheometer (BBR) were conducted to assess the evolution of viscosity, moisture content, high- and low-temperature performance, and morphological characteristics of micro-foamed asphalt over the foaming period. The results shows that the optimal dosages of KAl(SO ₄ ) ₂ · 12H ₂ O, Na ₂ CO ₃ · 10H ₂ O, and Na ₂ HPO ₄ · 12H ₂ O are 3%, 5%, and 1%, respectively, achieving viscosity reduction rates ranging from 9.92% to 14.62%. Compared to mechanically foamed asphalt, the micro-foamed asphalt exhibited improved physical properties, including an approximately 40% increase in low-temperature ductility and a 60% enhancement in viscosity-reduction stability. Relative to conventional warm-mix processes, the micro-foamed asphalt showed improvements of approximately 141% in fatigue resistance and 215% in cracking resistance. The viscosity-reducing effect remained above 70% for up to 2 h, while moisture content decreased exponentially during micro-foaming, with the final residual water content below 0.05%. Furthermore, a strong linear correlation was observed between apparent and internal bubble sizes, whereas the apparent bubble density exhibited a logarithmic relationship with internal bubble density. These findings demonstrate that the internal foaming state can be effectively characterized by analyzing the apparent bubble parameters of micro-foamed asphalt.

To investigate the expansion deformation of predisintegrated shale as subgrade soil and develop a calculation model to describe its expansion characteristic, the nonloaded and loaded expansion tests as well as expansion force tests were conducted on the typical predisintegrated shale under varying conditions. The results show that the expansion rate of compacted predisintegrated shale is greatly affected by initial water content, dry density, and overburden load, and that its expansion characteristics can be divided into three stages. After compaction, the expansion force of predisintegrated shale has a strong correlation with the initial dry density and initial water content, and 1.45 g·cm−3 can be used as threshold density for the rate of expansion force growth. Moreover, a comprehensive calculation model for the expansion rate and expansion force considering the coupling effects of various factors was proposed. This study proposes an alternative subgrade material using shale, which can efficiently save land resources and reduce engineering costs.

To reduce the harmful emissions generated during the use of bitumen binder. Tourmaline powder and organic montmorillonite (TP/OMMT) were used to prepare an environmentally friendly bitumen binder. First, the effect of TP/OMMT on the bitumen binder performance and storage stability was evaluated. Then, a self-designed device was used to analyze the fume production characteristics of TP/OMMT bitumen binder under various conditions. Finally, the extent of reduction and suppressing on 16 polycyclic aromatic hydrocarbons (PAHs) in bitumen fume by TP/OMMT was analyzed using gas chromatography–mass spectrometry (GC-MS). The results showed that TP/OMMT could form a uniformly dispersed state in bitumen binder and improved the high-temperature deformation resistance, as well as the low-temperature cracking resistance of bitumen binder. Bitumen fume production is greatly influenced by heating temperature, heating time, and exposure area. Compared with unmodified bitumen binder, the fume production of TP/OMMT modified bitumen binder was significantly reduced, where the fume production was reduced by 69.2 %. In addition, TP/OMMT significantly reduced 16 PAHs in bitumen fumes and the potentially carcinogenic high relative molecular mass was reduced by 45.2 %. The results provide implications for inhibiting the volatilization of hazardous substances in bitumen binder.

The advantages of asphalt pavement in terms of driving comfort, construction efficiency, and ease of maintenance have established it as the predominant choice for high-grade pavements at present. However, being highly sensitive to temperature and stress, asphalt performance is significantly influenced by external environmental conditions and loading, making it susceptible to various distress phenomena. Particularly in high-latitude regions, asphalt pavement cracking severely limits asphalt pavement’s functional performance and service lifespan under cold climatic conditions. To enhance the low-temperature cracking resistance of asphalt pavement in cold regions, tools such as VOS viewer 1.6.20 and Connected Papers were utilized to systematically organize, analyze, and summarize relevant research from the past 40 years. The results reveal that temperature shrinkage cracks and thermal fatigue cracks represent the primary forms of asphalt pavement distress in these regions. Cracking in asphalt pavement in cold regions is primarily influenced by structural design, pavement materials, construction technology, and climatic conditions. Among these factors, surface layer stiffness, base layer type, and the rate of temperature decrease exert the most significant impact on cracking resistance, collectively accounting for approximately 45.4% of all cracking-related factors. The low-temperature performance of asphalt pavement can be effectively improved through several strategies, including adopting full-thickness asphalt pavement with a skeleton-dense structure or reduced average particle size, incorporating functional layers, appropriately increasing the thickness of the upper layer and the compaction temperature of the lower layer, utilizing continuous surface layer construction techniques, and applying advanced materials. High-performance modifiers such as SBR and SBS, nanomaterials with good low-temperature performance, and warm mixing processes designed for cold regions have proven particularly effective. Among various improvement methods, asphalt modification has demonstrated superior effectiveness in enhancing the deformation capacity of asphalt and its mixtures, significantly boosting the low-temperature performance of asphalt pavements. Asphalt modification accounts for approximately 50% of the improvement methods evaluated in this study, with an average improvement in low-temperature performance reaching up to 143%. This paper provides valuable insights into the underlying causes of cracking distress in asphalt pavements in cold regions and offers essential guidance for improving the service quality of such pavements in these challenging environments.