Archives of Civil and Mechanical Engineering最新文献

This study investigates the mechanical, thermal, and durability performance of one-part geopolymer foam concrete (GFC) incorporating boiler ash (BA) as a partial replacement for fly ash (FA) and polypropylene fibers (PPF). Nine distinct mixtures were prepared with varying BA replacement levels (0%, 10%, and 20%) and PPF contents (0%, 0.5%, and 1%). Comprehensive testing was conducted to evaluate compressive and flexural strength, thermal conductivity, porosity, water absorption, sorptivity, freeze-thaw resistance, and high-temperature durability. The experimental results indicate that replacing FA with BA enhances the geopolymer matrix’s mechanical and durability properties through improved gel formation and matrix densification. The optimal mixture, containing 20% BA and 0.5% PPF, achieved a 41.52% increase in compressive strength compared to the reference mixture (0% BA, 0% PPF). This mixture also exhibited the lowest porosity (23.82%), water absorption (16.76%), and sorptivity (8.28%), along with the highest thermal conductivity (0.619 W/mK). However, mixtures with higher BA and PPF contents experienced reduced high-temperature resistance, with strength losses of 16.2% and 27.1% observed at 400 °C and 900 °C, respectively. Durability assessments revealed significant improvements in freeze-thaw performance. The optimized mixture demonstrated minimal weight loss and significant compressive strength gains after 15 freeze-thaw cycles. Microstructural analysis confirmed the synergistic effects of BA and PPF in enhancing the matrix’s densification, reducing pore connectivity, and bridging micro cracks. Additionally, BA’s high calcium content contributed to the formation of dense C-S-H and C-A-S-H gels, which played a crucial role in enhancing strength and reducing permeability. This study underscores the potential of BA as a sustainable alternative to FA in GFC production, highlighting its role in waste valorization and environmental sustainability. The findings provide valuable insights for optimizing BA and PPF content in GFC formulations, promoting their application in eco-friendly and high-performance construction materials.

In this study, the effects of incorporating recycled polypropylene-based straws into a cement matrix in the form of foam concrete on thermal insulation performance, mechanical strength, and environmental durability were investigated. Within the experimental program, nine different plastic-reinforced mixtures and a reference mixture were prepared using three different straw lengths (0.5 cm, 1.0 cm, and 2.0 cm) and three different volume ratios (0.5%, 1.0%, and 2.0%). Density, compressive strength, thermal conductivity, water absorption rate, apparent porosity, mass loss in sulfate and acidic environments, and durability following exposure to high temperatures were used to evaluate the properties of both fresh and hardened concrete. Besides, SEM imaging was conducted to analyze the microstructure. The findings indicated that the best balance performance was obtained in the 10WS series (with 1.0 cm-long straw at a ratio of 1%). The mixture had a porosity of 6.46% and a compressive strength of 22.67 MPa. Furthermore, thermal conductivity decreased by up to 30% compared to the reference mixture. The addition of plastic straws was found to have limiting effects on environmental durability; specifically, the 20WS series experienced mass loss exceeding 5% in environments containing sulfate. In conclusion, the re-use of waste plastic straws as construction materials offers thermal insulation advantages; however, it may have adverse effects on mechanical and environmental performance if the optimal content and sizing are not achieved. This study presents significant findings on the controlled use of waste plastics in the sustainable development of materials.

The influence of abrasive water jet (AWJ) machining process parameters, including the path shift factor s, on the geometric characteristics of textured surfaces was investigated. The path shift factor s is defined as the path shift b to the diameter of the mixing nozzle d, determining the degree of jet overlap and thus the resulting surface texture. The experimental results showed that path shift factor in the range of s = 1.0–0.8 enabled the formation of textures with a distinct periodic and unidirectional structure, whereas path shift factor of s ≤ 0.4 led to surface smoothing and a reduction in structural features. Path shift factor in the range of s = 0.3–0.5 enabled the creation of a homogeneous surface with minimal irregularities, while maintaining a balance between roughness and functionality. Additionally, groove analysis revealed significant differences in their geometry depending on the path shift factor of the working head with groove width and depth at s = 0.8 reduced by 23% and 31%, respectively, compared to s = 1.0. Overlapping passes improved surface uniformity, which may positively affect wear resistance and load-carrying capacity. Moreover, grinding the upper fragments of surfaces textured with s = 1.0 and s = 0.9 contributed to a favorable reduction in roughness and enhanced load-bearing performance. Results were also presented for a different texturing strategy obtained by modifying parameters typical of cutting to form shallow grooves. The findings emphasize that selecting appropriate abrasive water jet texturing process parameters enables effective control of surface geometry, supporting the design and optimization of scanning-based texturing strategies for industrial applications, particularly in components such as bearings, gears, and sliding surfaces where durability and uniform load transfer are critical.

This study investigates the running safety of a decelerating train on bridges subjected to near-fault pulse-like ground motions, with particular attention to the effects of pulse parameters and traveling wave velocity through synthetic seismic excitations. The analysis focuses on the dynamic interaction between the train and bridge, emphasizing the influence of pulse period, amplitude, and wave propagation velocity on both running safety and structural responses. The results indicate that larger pulse amplitudes significantly aggravate dynamic response of both the train and bridge, especially in the lateral direction, thereby increasing derailment risk. Pulse periods of 1–3 s tend to induce stronger responses amplitudes due to resonance effects, whereas longer periods mitigate the response amplitudes and enhance system stability. Traveling wave velocities exceeding 900 m/s produce nearly uniform seismic excitation, simplifying safety evaluations since further increases in velocity exert negligible impact on system dynamics. Moreover, the Velocity-Related Spectral Intensity (VSI) index exhibits greater sensitivity to deceleration-induced running safety than the conventional Spectral Intensity (SI) index, confirming its effectiveness as a seismic safety metric. These findings provide valuable insights into the seismic performance of train-bridge systems and offer practical guidance for improving the safety assessment and seismic design of railway infrastructures in earthquake-prone regions.

In the pursuit of sustainable infrastructure, the development of eco-friendly cement is vital. Geopolymers of the N–(C)–A–S–H network performed better, but there is a significant variation in microstructural changes. This study examines the effect of a fly ash and GGBS blend (1:1) geopolymers, activated by either NaOH (SH) or sodium silicate (SS), on their acid durability through the mechanical and microstructural properties of geopolymers FG_SH and FG_SS. The surface and core parts of the samples were analysed using multiple techniques. FG_SH retained 70% compressive strength after 90 days in 10% H₂SO₄, while FG_SS retained 55%, with the control maintaining strength of 30 ≤ 40 MPa. The FTIR band of (Si–O–Si/Al) from control samples showed a blue shift from 975 to 1080–1090 cm^–1 in the acid-corroded surface of FG_SS″ and FG_SH″, which is attributed to the highly polymerised silica gel. The sharp peak around 667 cm⁻¹ is the evident presence of the acid corrosion by-product of calcium sulphate. The dissolution of calcium-based gel affects the Al–O linkages at the Al^IV site in the zeolitic framework, which was evident from the disappearance of the Q¹ to Q³ environment from ²⁹Si NMR. δ_27Al −8.6 ppm, indicating the presence of aluminium sulphate, which confirms the needle form of ettringite in SEM analysis. A shift in δ_27Al from 62 to 42 ppm confirmed poorly crystalline C–(N)–A–S–H or amorphous N–A–S–H gel in FG_SS″. An ion exchange reaction mechanism was proposed to explain corrosion behaviour.

This study explores the structural behaviour of reinforced recycled aggregate concrete (RAC) columns confined with post-tensioned metal straps (PTMS) through experimental testing and numerical analysis. Twelve specimens with varying slenderness values (λ = 6.9, 13.9, 41.6) and confinement ratios (ρ_v = 0, 0.20, 0.27, 0.53) were tested in compression, including eight confined columns. The experimental results demonstrate that at the highest confinement ratio (ρ_v = 0.53) and the largest slenderness value (λ = 41.6), PTMS confinement significantly increased axial deformation by up to 19% and load capacity by 18%, enhancing column performance. These experimental results were used to calibrate numerical models in ABAQUS^® software. Finite Element Analysis (FEA) proved highly accurate, with nearly all errors staying under 8% for load capacity and 9% for deformability. FEA results revealed that confinement reduces P-Δ effects and improves stability, with critical buckling loads (P_cr) increasing by 174% in slender columns at high confinement (ρ_v = 0.53). The results confirmed experimental observations and offered additional insights into the effects of slenderness, extending beyond the limitations of the experiments. While light and moderate PTMS confinement enhances the strength of short columns, more slender columns require dense confinement to reduce lateral instability and bending. The study contributes the better understanding of RAC column behaviour with active confinement, encourages to use RAC in structural applications.

Copper coatings production increases due to the society awareness of their great anti-pathogenic properties. However, such coatings must show a set of requirements among which the corrosion resistance plays a key role. This study focused on determining the corrosion resistance of newly designed copper-titania composite coatings enriched with TiO₂ nanoparticles. The series of Cu-TiO₂ coatings have been produced using electroless plating process and different NiSO₄·7H₂O concentration in the bath solution. Composite and copper coatings were examined by Scanning Electron Microscopy and tested using potentiodynamic measurements and Electrochemical Impedance Spectroscopy. Scanning Electron Microscopy observations revealed that both Cu and Cu-TiO₂ coatings exhibit globular morphology without porosity. Electron microscopy analyses confirmed that titania nanoparticles has been incorporated into the copper matrix of composite coatings and also that the grain size of copper coatings and composite, produced under the same plating conditions, is identical. X-ray diffraction showed the highest nickel intensity at the lowest NiSO₄ concentration, indicating its impact on coating thickness. Corrosion studies confirmed that copper-titania coatings also may offer the corrosion protection.

Determining the mechanical properties of thin films presents significant challenges due to their nanometer-scale thickness. The separation of thin films from their substrates for standard plastometric testing is often difficult, if not impossible, complicating the direct measurement of their properties. Consequently, nanoindentation tests, which involve using small indenters and analyzing force-displacement curves, are commonly employed to assess the mechanical properties of thin films. However, experimental methods alone may be insufficient for accurately determining these properties for such thin films. This paper proposes an approach that combines numerical modelling of nanoindentation tests with the finite element method and inverse analysis to determine the optimal material constants for the substrate and thin film. The study focuses on TiN thin films deposited on silicon and stainless steel substrates as case studies. Prior to extracting the properties of the thin films, a comprehensive numerical accuracy analysis of the nanoindentation model was conducted. This involved investigating the impact of the digital model on the accuracy of results, comparing 2D and 3D models to optimize computational efficiency, and analysing the effect of finite element mesh discretization. The critical importance of accurately representing the indenter shape for reliable results was also highlighted. Following model validation, a series of nanoindentation simulations were performed on silicon and subsequently on the TiN/Si structure, enabling the separate determination of material constants for the substrate and the TiN thin film. The procedure was then applied to the TiN/SS structure for verification. The findings demonstrate that this approach enables the determination of the as-deposited thin film material properties based solely on nanoindentation tests and a robust numerical model, and it can be extended to other thin films.

Carbon fiber-reinforced cement mortar (CFRCM) is widely employed in structural reinforcement and health monitoring owing to its high strength and superior electrical conductivity. However, chloride content significantly influences both the mechanical performance and electrical conductivity of CFRCM bundles. In this study, the pull-out tests on CFRCM bundles with chloride concentrations ranging from 0% to 5% were carried out. The results revealed that peak load decreases progressively when chloride content exceeds 1%, while peak displacement remains consistent across all specimens at approximately 0.6 mm. Concurrently, the bond strength of the matrix exhibits a gradual decline with increasing chloride content, though the electrical properties of CFRCM bundles remain unaffected by chloride presence. Based on the test outcomes, there was a reduction in the peak load of the previous model design. Furthermore, the prediction accuracy of the modified model has been improved by as much as 86.25%. These findings provide a theoretical foundation for leveraging CFRCM in reinforcement and structural health monitoring of concrete infrastructure exposed to chloride-rich environments.

To simplify reinforcement detailing and enhance anchoring behavior, steel–polyethylene hybrid fiber-reinforced engineered cementitious composites (HECC) were applied in the joint core region instead of conventional concrete. Four stirrup-free HECC/RC interior joints featuring varying beam reinforcement anchorage lengths (7d, 9d, 11d, 15d) and two anchoring methods (continuous through the joint and overlapping) were designed and tested. Experimental results revealed anchoring failure when the beam reinforcement anchorage length was reduced to 9d. The incorporation of HECC significantly mitigated damage within the core region and improved the overall performance of the joint. Notably, even with the complete removal of stirrups, no delamination of the cover layer or crushing of HECC was observed in the core region. Insufficient anchorage diminished load-carrying capacity, accelerated bearing capacity degradation, and lowered the energy dissipation of joint specimens. In addition, the bond damage of continuous longitudinal reinforcement was more severe than that of the straight anchored one, resulting in increased slip of the beam reinforcement. Based on seismic performance and bond stress-slip analysis, a beam reinforcement anchorage length of 15d was recommended to maximize HECC’s exceptional bonding performance and ensure the seismic reliability of joint. Finally, a formula with acceptable accuracy for the shear bearing capacity of stirrup-free HECC interior joint, accounting for the influence of fiber reinforcement, was established based on the diagonal compressive strut mechanisms.