Reclaimed asphalt pavements (RAP) with reutilizing aged binders is very topical given their economic benefits. In particular, hot central-plant recycled technology is commonly used nowadays. In the hot recycled mixtures, virgin asphalt gradually diffuses into the aged one during the mixing process. The interaction on the virgin asphalt-RAP interface is critical for the reclamation of aged binders. However, the aforementioned diffusion behavior in reclaimed mixtures is not well comprehended. This study performed molecular dynamics (MD) simulation of the virgin asphalt-RAP interface diffusion behavior. Based on a four-component separation test, the molecular models of asphalt with different aging degrees were constructed, and their feasibility was verified by assessing the thermodynamic properties. Multiple MD simulations were performed to evaluate the effects of reclaimed mixture's manufacturing factors, including time, temperature, aging degree of aged binders, and mineral fillers content on the interfacial diffusion efficiency. The diffusion process of virgin asphalt was subdivided into three stages according to the molecular motion paths and system energy change. The impact of manufacturing factors on the diffusion rate of virgin binders was found to be significant, but their effect on the diffusion rate of asphalt mastic was found to be relatively weak. Gel permeation chromatography (GPC) was performed to evaluate the diffusion behavior of the virgin asphalt, which results were in good agreement with the simulated ones. The diffusion process of virgin asphalt was promoted by extending diffusion times and temperatures, and the optimal values varied with the aging degree of aged binders. As the mineral fillers content of asphalt increases, the effect of altering diffusion temperature on the blending efficiency is reduced.
To address the impacts of the coupling of multiple risk factors on the safe operation of the Tiantai Mountain Tunnel Cluster (MTC) in the Qinling mountains, China, key risk factors were identified and controlled to improve the safety risk management of the tunnel and reduce the traffic accident (TA) rate. TA data for the MTC from 2021 to 2024 were obtained and five level-1 and 23 level-2 risk factors affecting tunnel safety were identified. The level-1 risk factors were found to be people, vehicle, road, environment and management. An integrated model of analytic hierarchy process (AHP), the N–K model (NKM) and social network analysis (SNA) was used to form a new risk coupled analysis framework. The NKM evaluated coupling in TA cases, while the AHP model generated a risk matrix that was visualised through SNA, focusing on centrality, accessibility and cohesive subgroups. The results showed that, the larger the number of risk factors involved, the higher the risk coupling value and the greater the TA risk. Notably, risks taken by drivers was found to contribute to stronger multi-risk coupling involving ‘people–vehicle–environment’. Key factors identified include safety management systems as well as adverse weather conditions. These insights highlight critical risk factors and provide a basis for improved decision making regarding traffic safety.
Under global warming, the understanding of regional drought heterogeneity, drivers, and future persistence remains limited. Utilizing the Temperature Vegetation Dryness Index (TVDI, 2001-2020) and combining Theil-Sen trend analysis, Mann-Kendall test, partial correlation analysis, and Hurst exponent, this study analyzes global drought patterns, drivers, and persistence. Global drought changes exhibit significant spatial heterogeneity, exemplified by persistent intensification in Europe and an initial increase followed by subsequent mitigation in the Amazon. In terms of driving factors, drought is positively correlated with temperature in high-latitude regions (e.g. North America and Siberia), while it is primarily controlled by precipitation in arid regions. Compared to the period of 2001-2010, drought intensification became more widespread during 2011-2020, and its persistent nature suggests that most affected areas will continue to face sustained drought risks in the future. These findings underscore the necessity for region-specific adaptation strategies and provide valuable insights for drought risk assessment.
Atmospheric corrosion is one of the main factors leading to the failure of steel structures. The corrosion resistance performance of weathering steel-concrete composite beams seriously affects the structural operation and service. Therefore, it is significant to investigate the mechanism of atmospheric corrosion in concrete deck slabs and weathering steel beams, and to analyze the corrosion characteristics of weathering steel-concrete composite beams quantitatively. At present, there is a lack of research in the field of numerical simulation of pitting corrosion of weathering steels. The mechanism of the chromium and nickel elements in weathering steels for corrosion performance needs to be further explored. In this study, accelerated corrosion experiments were carried out on designed specimens of reinforced concrete deck slabs, as well as carbon and weathering steel beams, respectively. After that, finite element simulation model was established using COMSOL to analyze the evolution of steel reinforcement rust layer in reinforced concrete, and to investigate the development of carbon steel pitting corrosion. By introducing chromium and nickel elements into the pitting corrosion model, the protective effect of the corrosion rust layer on the pitting corrosion process of weathering steel was revealed. This filled the gap in numerical simulation of pitting corrosion of weathering steels and provided a reference for the time-varying corrosion of weathering steels. By combining experiments and numerical models, the time-varying corrosion of materials in corrosion conditions was studied for steel-concrete composite beams, provided a reference for the corrosion resistance design of steel-concrete composite beams. According to the corrosion morphology, kinetics, and electrochemical results, the size of corrosion pits and the corrosion rate of weathering steel were smaller than those of carbon steel due to the protection of corrosion products, and it showed better corrosion resistance. The numerical simulation results also demonstrated that chloride ions diffused along the depth direction in concrete, and the corrosion rate of steel reinforcement was lower under the protection of concrete.
This study investigates vortex-induced vibrations (VIVs) on dual parallel suspenders using wind tunnel experiments and employs a two-degree-of-freedom setup for each circular cylinder to closely simulate actual structural conditions. The VIV responses of dual cylinders exhibit notable deviations and complexity due to aerodynamic interaction. Results indicate a significant shift in the VIV lock-in range towards higher values for dual cylinders, compared to single ones. Both upstream and downstream cylinders demonstrate lower maximum VIV amplitudes than the single-cylinder. The cylinders exhibit effects of negative aerodynamic damping within the VIV process, with the aerodynamic damping becoming more pronounced as amplitude increases. Additionally, the timedependent phase relationship between the cylinders contributes to these variations in response. Further analysis of surface wind pressure distribution reveals that aerodynamic interference in dual-cylinder systems leads to intricate pressure patterns and modal behaviors.
