Noise barriers play a crucial role in mitigating railway noise, with the aerodynamic pressure exerted by passing trains being a key factor in their structural design, particularly for those installed along high-speed railways. While previous studies have focused on the effects of train speed, geometry, and distance from the track centre, and have developed models incorporating these factors, limited attention has been given to the impact of bilateral layouts and barrier height on this pressure. Quantitative assessments of these two factors remain scarce, and existing pressure calculation models inadequately address their influence. This study addressed these gaps by employing computational fluid dynamics (CFD) simulations, validated by field test data, to qualitatively and quantitatively analyze the effects of barrier layout and height on the aerodynamic pressure acting on vertical noise barriers. The results demonstrate that two distinct transient pressure fluctuations over time are generated by the train’s nose and tail, in agreement with the findings of the field tests. A bilateral layout increases peak pressure by up to 8.5%, particularly as the distance to the train centreline decreases. Moreover, increasing barrier height from 2 to 4 m resulted in a maximum pressure amplification of 13.23%, though the amplification rate diminished with further height increases. To address the limitations of existing pressure calculation models, an exponential model was developed to account for the amplification effect of bilateral layouts, while a logarithmic correction factor was introduced to account for barrier height. These models were integrated into a comprehensive aerodynamic pressure calculation framework, effectively capturing the combined impacts of barrier layout and height. Validated through simulations, the proposed model offers a more accurate and practical approach for predicting train-induced aerodynamic pressure on noise barriers, providing valuable insights to inform their structural design.

Geopolymers represent an innovative eco-friendly repair material due to exceptional mechanical properties and durability under high temperatures as well as in acidic and marine environments. This study applied molecular dynamics simulations to investigate the bonding mechanisms, interfacial interactions, and failure processes at the interfacial transition zone (ITZ) between geopolymer mortar and ordinary Portland cement concrete (OPC) under varying temperatures and moisture conditions. Results indicate that moderate temperature increases enhance interfacial interactions and bonding strength, whereas excessive heat compromises chemical bond stability, leading to reduced strength. Fracture behavior across different temperatures is characterized by three distinct stages, each demonstrating notable fracture toughness. Additionally, moisture presence at the interface alters interaction dynamics, reducing both bonding strength and ductility.

Coal bottom ash (CBA) is recovered from thermal power plants; it is an essential byproduct of the coal industry, and dumping on open land is the most significant environmental risk. Sustainably using CBA can help in alleviating ecological problems. Therefore, this study investigates the possibilities of utilizing CBA as a sand replacement in concrete production. A series of tests, including slump test, compressive strength (CS), water absorption, and water sorptivity of various bottom ash-based concrete mixes, were evaluated at curing ages of 7, 28, and 90 days for the desired strength of M25 and M35 concrete. Additionally, to determine the CS of the CBA concrete support vector regression was used, and the hyperparameters were optimized using particle swarm optimization (PSO-SVR) and jellyfish search optimization (JSO-SVR). Besides the outcomes of experiments, the data from previously published studies was also compiled and utilized for the prediction models. Experimental results reveal that M25 and M35 concrete of Sahiwal ash exhibited 10 %, 11 % and 11.8 %, 10.3 % higher CS with 25 % and 50 % CBA at 90 days. Similarly, M25 and M35 concrete of Sheikhupura ash, the CS increased by 8.3 % and 10 % with 25 % CBA at 90 days. Higher CBA content raises water absorption and sorptivity, indicating decreased durability. Increasing CBA content reduces concrete workability due to the hygroscopic nature of CBA particles. The higher specific gravity of CBA enhances strength development, yielding better-quality concrete. In contrast, the outcomes of the JSO-SVR models exhibited R2 for the training, testing, and validation dataset, which were 0.974, 0.961, and 0.9601, respectively. Furthermore, the JSO-SVR predictions were interpreted using SHapley Additive exPlanations (SHAP). The SHAP analysis revealed that sand, curing age, and cement were the most influential features affecting CS.

The thermal power plants generate a significant amount of coal bottom ash (CBA), which poses environmental hazards. Effective utilization of CBA is essential to mitigate its adverse environmental impacts. In this study, the feasibility of using CBA-from two coal-fired power plants in Punjab, Pakistan, namely Sahiwal (SWL) and Sheikhupura (SKP)-as a partial sand replacement in concrete was investigated to promote sustainable concrete production. A series of concrete mixtures and experiments were conducted, including evaluations of Flexural Strength (FS) and Split Tensile Strength (SPT) at curing ages of 7, 28, and 90 days for M25 and M35 grade concrete. To enhance predictive capabilities, eXtreme Gradient Boosting (XGBoost) and Light Gradient Boosting Machine (LGBM) models optimized using Particle Swarm Optimization (PSO) were employed to accurately predict the FS and SPT of CBA-based concrete. In addition to experimental data, previously published datasets were incorporated to improve model robustness. Experimental results indicated that concrete incorporating SWL-CBA achieved FS and SPT values comparable to control mixes at 28 and 90 days for M25 and M35 grades when CBA replaced 25 % and 50 % of sand, respectively. However, SKP-CBA mixes consistently showed lower strength performance. The PSO-optimized XGBoost and LGBM models exhibited excellent predictive performance, with R² values exceeding 0.98 during training and reaching 0.96 during testing. Furthermore, SHapley Additive exPlanations (SHAP) analysis was used to interpret the PSO-LGBM model, revealing that curing age, the specific gravity (SG) of CBA, sand/cement ratio, and CBA, and curing age, cement content, water and CBA were the most influential features affecting FS and SPT, respectively. The study findings support the recommendation of using higher SG CBA as a sustainable partial sand replacement, contributing to natural sand conservation, while also highlighting the effectiveness of machine learning approaches in accurately modeling and optimizing concrete performance.

This paper investigates the current landscape of multiscale studies in concrete composites incorporating molecular dynamics (MD) methods. Through a thorough literature analysis, it was determined that finite element, discrete element, homogenization, microphysical characterization, and machine learning methods are better suited for integration with MD in multiscale studies of concrete composites. The paper delves into MD's application characteristics and the selection of force fields in multiscale studies and provides a summary of the combined applications between MD and various methods. Challenges identified include the optimization of MD simulations and the appropriate selection of combined methods. The conclusions underscore the growing recognition of MD's significance, advocating for rational multi-method integration in multiscale approaches to effectively advance research on concrete composites.

Fatigue significantly impacts engineering structures, especially reinforced concrete, which endures millions of cyclic loads over its service life. Understanding the progressive degradation of concrete’s mechanical properties under fatigue is critical. This paper reviews existing degradation models, encompassing stiffness degradation, strength degradation, and strain development models. Then, these models are compared in terms of accuracy and applicability, and potential research directions for concrete damage modeling under fatigue are proposed. This work aims to serve as a valuable resource for future investigations and engineering applications. 

Natural frequencies of engineering structures often vary with environmental temperature changes. For bridges, these variations can affect structural performance and potentially compromise the safety of pedestrian and vehicular traffic. The extent of this impact depends on bridge type and boundary conditions. One simply supported steel–concrete composite railway bridge in northern Sweden, where temperatures range from –40 °C to 30 °C, is investigated in this study. Using finite element analysis (FEA), the effects of temperature-induced changes in concrete properties, boundary constraints, and ballast stiffness on the bridge’s natural frequencies and modes are examined. Results show that: (1) As temperature decreases, the first, second and third natural frequencies increase by 12.41%, 20.08% and 16.92%, respectively; (2) the frequency–temperature relationship exhibits a trilinear behavior; and (3) temperature variations have a more pronounced effect on torsional modes than on bending modes. This study attempts to provide advice for the scheme and maintenance of railway bridges in cold regions.

Corrosion of steel reinforcement in concrete is a significant cause of structural failure, particularly in environments exposed to chloride ions and mechanical stress. The passivation film on steel reinforcement, composed of hematite or magnetite, plays a crucial role in protecting the steel from further corrosion. However, the intrusion of harmful ions or mechanical stress can compromise the film’s integrity, transforming it into a loose structure and accelerating the corrosion process, leading to structural failure. This study investigates the mechanical behaviors at the interfaces between corrosion products (hematite and magnetite) and C-S-H using reactive molecular dynamics. C-S-H and interfacial models incorporating hematite and magnetite were developed, with stress–strain analysis refined by filtering raw data and using true strain rather than engineering strain to improve the precision of the stress–strain responses. The results indicate that the Magnetite-CSH interface is more prone to loosening under external forces compared to the Hematite-CSH interface, thereby reducing its corrosion resistance. Structural evolution analysis under uniaxial tension highlights the detrimental effects of passivation film degradation on interfacial mechanical properties. This study contributes to improving the precision of stress–strain responses in MD models and facilitates comparison of mechanical properties at the nanoscale with results from other scales. The findings provide valuable guidance for improving the durability and performance of construction materials in corrosive environments, helping to bridge the gap between molecular-level simulations and macroscopic experimental data.

Amine functionalized solids demonstrate well potential in CO2 capture, but this modification may affect the potential water storage capacity of zeolites that possess natural interlinked channels. This study systematically examined the wetting characteristics of droplets on ZSM-5 [0 0 1] surfaces with amino silane modifications and structural water adsorption behaviors using molecular dynamics simulations. The interaction mechanisms between water molecules and particles within the structure were analyzed, and droplet wetting and penetration modes were proposed. The hydrophobicity enhanced by modified surfaces effectively decelerated the wetting process. Nevertheless, water molecules continued to penetrate the zeolite structure via surface cavities, albeit in reduced numbers as coverage increases. N atoms in the amino groups attracted water molecules to form weak hydrogen bond networks, and under the intrinsic driving forces of water molecules and competitive adsorption site occupation, the wetting and permeation processes of droplets were facilitated. Amine functionalized membranes reduced water flux during the membrane separation process, while high-concentration group modification achieved complete ion rejection. Deciphering the wetting and water transport mechanisms within the structure of zeolites and their modified surfaces at the molecular level aids in balancing the requirements of surface hydrophilicity and hydrophobicity along with structural water flux.